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1
NISSIM, Itzhak, Oksana HORYN, Bohdan LUHOVYY, Adam LAZAROW, Yevgeny DAIKHIN, Ilana NISSIM, and Marc YUDKOFF. "Role of the glutamate dehydrogenase reaction in furnishing aspartate nitrogen for urea synthesis: studies in perfused rat liver with 15N." Biochemical Journal 376, no. 1 (November 15, 2003): 179–88. http://dx.doi.org/10.1042/bj20030997.
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The present study was designed to determine: (i) the role of the reductive amination of α-ketoglutarate via the glutamate dehydrogenase reaction in furnishing mitochondrial glutamate and its transamination into aspartate; (ii) the relative incorporation of perfusate 15NH4Cl, [2-15N]glutamine or [5-15N]glutamine into carbamoyl phosphate and aspartate-N and, thereby, [15N]urea isotopomers; and (iii) the extent to which perfusate [15N]aspartate is taken up by the liver and incorporated into [15N]urea. We used a liver-perfusion system containing a physiological mixture of amino acids and ammonia similar to concentrations in vivo, with 15N label only in glutamine, ammonia or aspartate. The results demonstrate that in perfusions with a physiological mixture of amino acids, approx. 45 and 30% of total urea-N output was derived from perfusate ammonia and glutamine-N respectively. Approximately two-thirds of the ammonia utilized for carbamoyl phosphate synthesis was derived from perfusate ammonia and one-third from glutamine. Perfusate [2-15N]glutamine, [5-15N]glutamine or [15N]aspartate provided 24, 10 and 10% respectively of the hepatic aspartate-N pool, whereas perfusate 15NH4Cl provided approx. 37% of aspartate-N utilized for urea synthesis, secondary to the net formation of [15N]glutamate via the glutamate dehydrogenase reaction. The results suggest that the mitochondrial glutamate formed via the reductive amination of α-ketoglutarate may have a key role in ammonia detoxification by the following processes: (i) furnishing aspartate-N for ureagenesis; (ii) serving as a scavenger for excess ammonia; and (iii) improving the availability of the mitochondrial [glutamate] for synthesis of N-acetylglutamate. In addition, the current findings suggest that the formation of aspartate via the mitochondrial aspartate aminotransferase reaction may play an important role in the synthesis of cytosolic argininosuccinate.
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Pardo, Beatriz, Tiago B. Rodrigues, Laura Contreras, Miguel Garzón, Irene Llorente-Folch, Keiko Kobayashi, Takeyori Saheki, Sebastian Cerdan, and Jorgina Satrústegui. "Brain Glutamine Synthesis Requires Neuronal-Born Aspartate as Amino Donor for Glial Glutamate Formation." Journal of Cerebral Blood Flow & Metabolism 31, no. 1 (August 25, 2010): 90–101. http://dx.doi.org/10.1038/jcbfm.2010.146.
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The glutamate–glutamine cycle faces a drain of glutamate by oxidation, which is balanced by the anaplerotic synthesis of glutamate and glutamine in astrocytes. De novo synthesis of glutamate by astrocytes requires an amino group whose origin is unknown. The deficiency in Aralar/ AGC1, the main mitochondrial carrier for aspartate–glutamate expressed in brain, results in a drastic fall in brain glutamine production but a modest decrease in brain glutamate levels, which is not due to decreases in neuronal or synaptosomal glutamate content. In vivo13C nuclear magnetic resonance labeling with 13C2acetate or (1-13C) glucose showed that the drop in brain glutamine is due to a failure in glial glutamate synthesis. Aralar deficiency induces a decrease in aspartate content, an increase in lactate production, and lactate-to-pyruvate ratio in cultured neurons but not in cultured astrocytes, indicating that Aralar is only functional in neurons. We find that aspartate, but not other amino acids, increases glutamate synthesis in both control and aralar-deficient astrocytes, mainly by serving as amino donor. These findings suggest the existence of a neuron-to-astrocyte aspartate transcellular pathway required for astrocyte glutamate synthesis and subsequent glutamine formation. This pathway may provide a mechanism to transfer neuronal-born redox equivalents to mitochondria in astrocytes.
3
Hertz, Leif. "Brain Glutamine Synthesis Requires Neuronal Aspartate: A Commentary." Journal of Cerebral Blood Flow & Metabolism 31, no. 1 (November 10, 2010): 384–87. http://dx.doi.org/10.1038/jcbfm.2010.199.
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Inspired by the paper, ‘Brain glutamine synthesis requires neuronal-born aspartate as amino donor for glial glutamate formation’ by Pardo et al, a modified model of oxidation–reduction, transamination, and mitochondrial carrier reactions involved in aspartate-dependent astrocytic glutamine synthesis and oxidation is proposed. The alternative model retains the need for cytosolic aspartate for transamination of α-ketoglutarate, but the ‘missing’ aspartate molecule is generated within astrocytes during subsequent glutamate oxidation. Oxaloacetate formed during glutamate formation is used during glutamate degradation, and all transmitochondrial reactions, oxidations–reductions, and cytosolic and mitochondrial transaminations are stoichiometrically balanced. The model is consistent with experimental observations made by Pardo et al.
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Khalish, Mutiara, and Lathifah Yasmine Wulandari. "The Vitamin C Berpengaruh dalam Memperbaiki Kerusakan Hepar Akibat Pemberian Monosodium Glutamat." Jurnal Penelitian Perawat Profesional 2, no. 2 (March 14, 2020): 125–30. http://dx.doi.org/10.37287/jppp.v2i2.67.
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Konsumsi monosodium glutamat dalam jumlah berlebih dapat menyebabkan dampak berkaitan dengan kerusakan hepar yang ditandai adanya peningkatan kadar enzim aspartate transaminase dan alanine transaminase. Vitamin c berperan menjaga sistem imunitas tubuh dan mempercepat proses penyembuhan kerusakan hepar. Tujuan penulisan artikel ini adalah untuk mengetahui manfaat vitamin c sebagai upaya dalam memperbaiki kerusakan hepar akibat monosodium glutamat. Metode yang digunakan dalam artikel ini adalah penelusuran artikel melalui database Google Scholar, NCBI dan Elsevier. Tahun penerbitan pustaka adalah dari tahun 2010 hingga 2019 dengan 17 sumber pustaka. Hasil dari literatur review ini menunjukan bahwa vitamin c dapat mengurangi kerusakan hepar akibat monosodium glutamat dengan adanya penurunan kadar enzim aspartate transaminase dan alanine transaminase. Vitamin c dapat digunakan untuk melawan efek radikal bebas dari monosodium glutamat karena aktifitasnya sebagai antioksidan. Vitamin c berpengaruh dalam memperbaiki kerusakan hepar akibat pemberian monosodium glutamat.
Kata kunci: aspartate transaminase, alanine transaminase, monosodium glutamat, vitamin c
VITAMIN C AFFECT IN IMPROVING HEPAR DAMAGE CAUSED BY ADMINISTRATION OF MONOSODIUM GLUTAMATE
ABSTRACT
Excessive consumption of monosodium glutamate can cause effects related to liver damage which is marked by an increase in levels of the enzymes aspartate transaminase and alanine transaminase. Vitamin c plays a role in maintaining the body's immune system and accelerating the healing process of liver damage. The purpose of writing this article is to determine the benefits of vitamin c as an effort to repair liver damage due to monosodium glutamate. The method used in this article is article searching through Google Scholar, NCBI and Elsevier databases. The year of library publication is from 2010 to 2019 with 17 library sources. The results of this review literature show that vitamin c can reduce liver damage due to monosodium glutamate by decreasing levels of the enzymes aspartate transaminase and alanine transaminase. Vitamin C can be used to fight the effects of free radicals from monosodium glutamate because of its activity as an antioxidant. Vitamin C has an effect on repairing liver damage due to monosodium glutamate.
Keywords: aspartate transaminase, alanine transaminase, monosodium glutamate, vitamin c
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Martin, G., C. Michoudet, N. Vincent, and G. Baverel. "Release and fixation of CO2 by guinea-pig kidney tubules metabolizing aspartate." Biochemical Journal 284, no. 3 (June 15, 1992): 697–703. http://dx.doi.org/10.1042/bj2840697.
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1. The metabolism of L-[U-14C]aspartate, L-[1-14C]aspartate and L-[4-14C]aspartate was studied in isolated guinea-pig kidney tubules. 2. Oxidation of C-1 plus that of C-4 of aspartate accounted for 90-92% of the CO2 released from aspartate, whereas oxidation of the inner carbon atoms of aspartate (which occurs beyond the 2-oxoglutarate dehydrogenase step) represented only 8-10% of aspartate carbon oxidation. 3. The formation of [1-14C]glutamine and [1-14C]glutamate from [1-14C]aspartate and [4-14C]aspartate indicated that about one-third of the oxaloacetate synthesized from aspartate underwent randomization at the level of fumarate. 4. With [U-14C]aspartate as substrate, the percentage of the C-1 of glutamate and glutamine found radiolabelled after 60 min of incubation was 92.7% and 47.5% in the absence and the presence of bicarbonate respectively. 5. That CO2 fixation occurred at high rates in the presence of bicarbonate was demonstrated by incubating tubules with aspartate plus [14C]bicarbonate; under this condition, the label fixed was found in C-1 of glutamate, glutamine and aspartate, as well as in C-4 of aspartate, demonstrating not only randomization of aspartate carbon but also aspartate resynthesis secondary to oxaloacetate cycling via phosphoenolpyruvate carboxykinase, pyruvate kinase and pyruvate carboxylase. 6. The importance of CO2 fixation in glutamine synthesis from aspartate is discussed in relation to the possible role of the guinea-pig kidney in systemic acid-base regulation in vivo.
6
Nianhui, Zhang, and P. Ottersen Ole. "In Search of the Identity of the Cerebellar Climbing Fiber Transmitter: Immunocytochemical Studies in Rats." Canadian Journal of Neurological Sciences / Journal Canadien des Sciences Neurologiques 20, S3 (May 1993): S36—S42. http://dx.doi.org/10.1017/s0317167100048514.
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ABSTRACT:Quantitative immunogold cytochemistry at the electron microscopic level was used to assess the endogenous contents of glutamate, aspartate, homocysteic acid, and glutamine (a precursor of glutamate) in the cerebellar climbing fiber terminals. Of the three excitatory amino acids, only glutamate appeared to be enriched in these terminals. The climbing fiber terminals also displayed immunoreactivity for glutamine. The level of aspartate immunoreactivity was far higher in the nerve cell bodies in the inferior olive than in their terminals in the cerebellar cortex. Homocysteic acid immunolabelling was concentrated in glial cells including the Golgi epithelial cells in the Purkinje cell layer. Our immunocytochemical data indicate that glutamate is a more likely climbing fiber transmitter than aspartate and homocysteic acid.
7
Osbakken, M., D. N. Zhang, D. Nelson, and M. Erecinska. "Effect of cyclocreatine feeding on levels of amino acids in rat hearts before and after an ischemic episode." American Journal of Physiology-Heart and Circulatory Physiology 261, no. 6 (December 1, 1991): H1919—H1926. http://dx.doi.org/10.1152/ajpheart.1991.261.6.h1919.
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Feeding Sprague-Dawley rats for 3 wk a diet containing 1% by weight of cyclocreatine increased the reservoir of the high-energy phosphate compounds but also caused alterations in the levels of the two key amino acids, aspartate and glutamate. Both were decreased by approximately 50% in the presence of an unaltered content of glutamine. In vitro exposure of these hearts to sequential perfusion, global ischemia, and reperfusion in the absence of added amino acids resulted in changes in aspartate, glutamate, and glutamine that were different from those in hearts from control rats. In the cyclocreatine-fed group, aspartate concentration ([aspartate]) and [glutamate] fell after global ischemia, whereas [glutamine] was unaltered. [Glutamine] decreased, however, in the reperfusion period. In control hearts, the predominant effect was a steady decline in glutamine, which was accompanied by either less than 10% (after global ischemia) or 30-50% fall (after reperfusion) in [aspartate] and [glutamate]. The concentration of tissue Pi was smaller in hearts from cyclocreatine-fed rats and appeared to increase more slowly during ischemia. In the presence of rotenone and aminooxyacetate, heart homogenates catalyzed production of glutamate from glutamine, which was markedly stimulated by Pi and inhibited by H+. It is postulated that 1) phosphate-activated glutaminase is an important enzyme that determines cardiac [glutamate], 2) lower [phosphate] in hearts from rats fed cyclocreatine is responsible for the apparently lesser activity of glutaminase, 3) breakdown of the high-energy phosphate compounds and consequent rise in Pi activates glutaminase, and 4) slow breakdown of glutamine during global ischemia is a result of inhibition of glutaminase by H+.
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Baverel, G., G. Martin, and C. Michoudet. "Glutamine synthesis from aspartate in guinea-pig renal cortex." Biochemical Journal 268, no. 2 (June 1, 1990): 437–42. http://dx.doi.org/10.1042/bj2680437.
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1. Glutamine was found to be the main carbon and nitrogen product of the metabolism of aspartate in isolated guinea-pig kidney-cortex tubules. Glutamate, ammonia and alanine were only minor products. 2. Carbon-balance calculations and the release of 14CO2 from [U-14C]aspartate indicate that oxidation of the aspartate carbon skeleton occurred. 3. A pathway involving aspartate aminotransferase, glutamate dehydrogenase, glutamine synthetase, phosphoenolpyruvate carboxykinase, pyruvate kinase, pyruvate dehydrogenase and enzymes of the tricarboxylic acid cycle is proposed for the conversion of aspartate into glutamine. 4. Evidence for this pathway was obtained by: (i) inhibiting aspartate removal by amino-oxyacetate, an inhibitor of transaminases, (ii) the use of methionine sulphoximine, an inhibitor of glutamine synthetase, which induced a large increase in ammonia release from aspartate, (iii) the use of quinolinate, an inhibitor of phosphoenolpyruvate carboxykinase, which inhibited glutamine synthesis from aspartate, (iv) the use of alpha-cyano-4-hydroxycinnamate, an inhibitor of the mitochondrial transport of pyruvate, which caused an accumulation of pyruvate from aspartate, and (v) the use of fluoroacetate, an inhibitor of aconitase, which inhibited glutamine synthesis with concomitant accumulation of citrate from aspartate.
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Gundersen, Vidar, Frode Fonnum, Ole Petter Ottersen, and Jon Storm-Mathisen. "Redistribution of Neuroactive Amino Acids in Hippocampus and Striatum during Hypoglycemia: A Quantitative Immunogold Study." Journal of Cerebral Blood Flow & Metabolism 21, no. 1 (January 2001): 41–51. http://dx.doi.org/10.1097/00004647-200101000-00006.
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Postembedding immunocytochemistry was used to localize aspartate, glutamate, gamma-aminobutyric acid (GABA), and glutamine in hippocampus and striatum during normo- and hypoglycemia in rat. In both brain regions, hypoglycemia caused aspartatelike immunoreactivity to increase. In hippocampus, this increase was evident particularly in the terminals of known excitatory afferents—in GABA-ergic neurons and myelinated axons. Aspartate was enriched along with glutamate in nerve terminals forming asymmetric synapses on spines and with GABA in terminals forming symmetric synapses on granule and pyramidal cell bodies. In both types of terminal, aspartate was associated with clusters of synaptic vesicles. Glutamate and glutamine immunolabeling were markedly reduced in all tissue elements in both brain regions, but less in the terminals than in the dendrosomatic compartments of excitatory neurons. In glial cells, glutamine labeling showed only slight attenuation. The level of GABA immunolabeling did not change significantly during hypoglycemia. The results support the view that glutamate and glutamine are used as energy substrates in hypoglycemia. Under these conditions both excitatory and inhibitory terminals are enriched with aspartate, which may be released from these nerve endings and thus contribute to the pattern of neuronal death characteristic of hypoglycemia.
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Lietz, T., K. Winiarska, and J. Bryła. "Ketone bodies activate gluconeogenesis in isolated rabbit renal cortical tubules incubated in the presence of amino acids and glycerol." Acta Biochimica Polonica 44, no. 2 (June 30, 1997): 323–31. http://dx.doi.org/10.18388/abp.1997_4428.
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In isolated rabbit renal kidney-cortex tubules 2 mM glycerol, which is a poor gluconeogenic substrate, does not induce glucose formation in the presence of alanine, while it activates gluconeogenesis on substitution of alanine by aspartate, glutamate or proline. The addition of either 5 mM 3-hydroxybutyrate or 5 mM acetoacetate to renal tubules incubated with alanine + glycerol causes a marked induction of glucose production associated with inhibition of glutamine synthesis. In contrast, the rate of the latter process is not altered by ketones in the presence of glycerol and either aspartate, glutamine or proline despite the stimulation of glucose formation. Acceleration of gluconeogenesis by ketone bodies in the presence of amino acids and glycerol is probably due to (i) stimulation of pyruvate carboxylase activity, (ii) activation of malate-aspartate shuttle as concluded from elevated intracellular levels of malate, aspartate and glutamate, as well as (iii) diminished supply of ammonium for glutamine synthesis from alanine resulting from a decrease in glutamate dehydrogenase activity.
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Schuldt, Scott, Patsy Carter, and Tomas Welbourne. "Glutamate transport asymmetry and metabolism in the functioning kidney." American Journal of Physiology-Endocrinology and Metabolism 277, no. 3 (September 1, 1999): E439—E446. http://dx.doi.org/10.1152/ajpendo.1999.277.3.e439.
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Renal glutamate extraction in vivo shows a preference for the uptake ofd-glutamate on the antiluminal and l-glutamate on the luminal tubule surface. To characterize this functional asymmetry, we isolated rat kidneys and perfused them with an artificial plasma solution containing either d- orl-glutamate alone or in combination with the system [Formula: see text]specific transport inhibitor,d-aspartate. To confirm that removal of glutamate represented transport into tubule cells, we monitored products formed as the result of intracellular metabolism and related these to the uptake process. Perfusion withd-glutamate alone resulted in a removal rate that equaled or exceeded thel-glutamate removal rate, with uptake predominantly across the antiluminal surface;l-glutamate uptake occurred nearly equally across both luminal and antiluminal surfaces. Thus the preferential uptake ofd-glutamate at the antiluminal and l-glutamate at the luminal surface confirms the transport asymmetry observed in vivo. Equimolard-aspartate concentration blocked most of the antiluminald-glutamate uptake and a significant portion of the luminall-glutamate uptake, consistent with system [Formula: see text] activity at both sites. d-Glutamate uptake was associated with 5-oxo-d-proline production, whereas l-glutamate uptake supported both glutamine and 5-oxo-l-proline formation;d-aspartate reduced production of both 5-oxoproline and glutamine. The presence of system[Formula: see text] activity on both the luminal and antiluminal tubule surfaces, exhibiting different reactivity towardl- andd-glutamate suggests that functional asymmetry may reflect two different[Formula: see text] transporter subtypes.
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Benveniste, Helene, and David S. Warner. "Glutamate, Microdialysis, and Cerebral Ischemia." Anesthesiology 110, no. 2 (February 1, 2009): 422–25. http://dx.doi.org/10.1097/aln.0b013e318194b620.
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Elevation of the extracellular concentrations of glutamate and aspartate in rat hippocampus during transient cerebral ischemia monitored by intracerebral microdialysis. By Helene Benveniste, Jørgen Drejer, Arne Schousboe, Nils H. Diemer. J Neurochem 1984; 43:1369-74. Reprinted with permission of Blackwell Publishing. Rats were implanted with 0.3-mm-diameter dialysis tubing through the hippocampus and subsequently perfused with Ringer's solution at a flow rate of 2 ml/min. Samples of the perfusate representing the extracellular fluid were collected over 5-min periods and subsequently analyzed for contents of the amino acids glutamate, aspartate, glutamine, taurine, alanine, and serine. Samples were collected before, during, and after a 10-min period of transient complete cerebral ischemia. The extracellular contents of glutamate and aspartate were increased, respectively, eight- and threefold during the ischemic period; the taurine concentration also was increased 2.6-fold. During the same period the extracellular content of glutamine was significantly decreased (to 68% of the control value), whereas the concentrations of alanine and serine did not change significantly during the ischemic period. The concentrations of gamma-aminobutyric acid (GABA) were too low to be measured reliably. It is suggested that the large increase in the content of extracellular glutamate and aspartate in the hippocampus induced by the ischemia may be one of the causal factors in the damage to certain neurons observed after ischemia.
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He, Wenliang, Yongqing Hou, and Guoyao Wu. "253 Glutamate and glutamine are the major metabolic fuels in enterocytes of suckling piglets." Journal of Animal Science 97, Supplement_3 (December 2019): 68. http://dx.doi.org/10.1093/jas/skz258.141.
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Abstract Glutamate and glutamine are known to be important energy substrates in pig enterocytes, and aspartate has also been reported to be extensively catabolized by the rat small intestine. However, little is known about the relative role of amino acids, glucose and fatty acids in ATP production by enterocytes. In the present study, enterocytes isolated from 0-, 7-, 14- and 21-day-old piglets were used to determine the rates of oxidation of amino acids, fatty acids and glucose. Enterocytes were incubated at 37oC for 30 min in Krebs-Henseleit bicarbonate buffer (pH 7.4) containing 5 mM D-glucose and one of the following: 0.5–5 mM L-[U-14C]glutamate, 0.5–5 mM L-[U-14C]glutamine, 0.5–5 mM L-[U-14C]aspartate, 0.5–5 mM L-[U-14C]alanine, 0.5–2 mM L-[U-14C]palmitate, D-[U-14C]glucose, 0.5–5 mM [U-14C]propionate, or 0.5–5 mM [1-14C]butyrate. At the end of the incubation, 14CO2 produced from each 14C-labeled substrate was collected. Rates of oxidation of each substrate in enterocytes from all age groups of piglets increased (P < 0.01) progressively with increasing its extracellular concentrations. The rates of oxidation of glutamate, glutamine, aspartate, glucose by enterocytes from 0- to 21-day-old pigs were much greater (P < 0.01) than those for the same concentrations of alanine, palmitate, propionate, and butyrate. In cells from all age groups of piglets, rates of oxidation of, and ATP production from 5 mM glutamate or 5 mM glutamine were greater (P < 0.01) than those from 5 mM glucose and aspartate. Oxidation of alanine, propionate, butyrate and palmitate by enterocytes was limited. At each postnatal age, the oxidation of glutamate and glutamine produced more ATP than any other substrates. Our results indicated that glutamate and glutamine are the major metabolic fuels in enterocytes of 0- to 21-day-old pigs. Because of limited uptake of arterial glutamate by enterocytes, dietary glutamate is essential to the integrity and function of the pig small intestine.
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Li, Xinyu, and Guoyao Wu. "251 Oxidation of energy substrates in tissues of Largemouth bass (Micropterus salmoides)." Journal of Animal Science 97, Supplement_3 (December 2019): 68–69. http://dx.doi.org/10.1093/jas/skz258.142.
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Abstract Because of growing interest in producing Largemouth bass (HMB) as a source of high-quality protein for human consumption worldwide, it is imperative to understand the metabolism of nutrients (including amino acids and carbohydrate) in this aquatic animal. The present study tested the hypothesis that amino acids are oxidized at a higher rate than carbohydrates (e.g., glucose) and fatty acids (e.g., palmitate) to provide ATP for tissues of LMB fed a 45%-crude protein diet. The liver, intestine, kidney, and skeletal muscle were isolated from juvenile LMB and incubated at 26 °C (the body temperature of LMB) for 2 h in 1 ml of oxygenated Krebs–Henseleit bicarbonate buffer (pH 7.4) containing a mixture of nutrients (2 mM glutamate, 2 mM glutamine, 2 mM aspartate, 2 mM alanine, 2 mM leucine, 5 mM glucose, and 2 mM palmitate). The rate of oxidation of each energy substrate was determined by using [U-14C]-labeled glutamate, glutamine, aspartate, alanine, leucine, glucose, or palmitate and collecting 14CO2 from each tracer. Results indicated that aspartate, glutamate and glutamine were extensively oxidized in all the four tissues and contributed to 67% of total ATP production. Glutamate contributed to more ATP than glutamine in the intestine, whereas similar amounts of ATP were produced from glutamate and glutamine in the liver, kidneys and skeletal muscle. In all the four tissues, rates of oxidation of alanine, leucine, palmitate and glucose were low and each of those nutrients contributed to < 10% of total ATP production. Together, the oxidation of aspartate, glutamate, glutamine, alanine plus leucine provided 82–85% of total ATP for the liver, intestine, kidney, and skeletal muscle. We conclude that amino acids, rather than glucose and long-chain fatty acids, are the primary energy substrates in the major tissues of Largemouth bass.
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Simon, E. E., C. Merli, J. Herndon, and L. L. Hamm. "Contribution of luminal ammoniagenesis to proximal tubule ammonia appearance in the rat." American Journal of Physiology-Renal Physiology 259, no. 3 (September 1, 1990): F402—F407. http://dx.doi.org/10.1152/ajprenal.1990.259.3.f402.
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The contribution of luminal ammoniagenesis in the late proximal convolute tubule (PCT) via phosphate-independent glutaminase [gamma-glutamyltransferase (gamma-GT)] remains controversial. If this pathway is important, it must rely on glutamine secretion, because filtered glutamine is reabsorbed in the early PCT. The contribution of gamma-GT to luminal ammoniagenesis was tested by use of in vivo microperfusion in conjunction with a new microfluorometric assay for glutamate. We first confirmed that aspartate completely blocked glutamate uptake in the PCT. Furthermore, the gamma-GT inhibitor acivicin completely eliminated glutamate entry, showing that passive glutamate entry was negligible. Thus the accumulation of glutamate can be used as an estimate of luminal glutamine deamidation. L-Phenylalanine was used to inhibit glutamine loss, and hippurate was used to stimulate gamma-GT activity; therefore luminal glutamine conversion to glutamate was promoted. Perfusing the tubule at 30 nl/min with a solution containing 10 mM each of hippurate, phenylalanine, and aspartate resulted in a glutamate delivery of 1.08 +/- 0.12 pmol.min-1.mm-1. Ammonia appearance was 10-fold higher, averaging 11.5 +/- 1.3 pmol.min-1.mm-1 under these same conditions. Thus the luminal conversion of glutamine to glutamate via gamma-GT is a small component of total ammoniagenesis in this segment.
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Andersen, Jens Velde, Jakob Dahl Nissen, Sofie Kjellerup Christensen, Kia Hjulmand Markussen, and Helle Sønderby Waagepetersen. "Impaired Hippocampal Glutamate and Glutamine Metabolism in the db/db Mouse Model of Type 2 Diabetes Mellitus." Neural Plasticity 2017 (2017): 1–9. http://dx.doi.org/10.1155/2017/2107084.
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Type 2 diabetes mellitus (T2DM) is a risk factor for the development of Alzheimer’s disease, and changes in brain energy metabolism have been suggested as a causative mechanism. The aim of this study was to investigate the cerebral metabolism of the important amino acids glutamate and glutamine in the db/db mouse model of T2DM. Glutamate and glutamine are both substrates for mitochondrial oxidation, and oxygen consumption was assessed in isolated brain mitochondria by Seahorse XFe96 analysis. In addition, acutely isolated cerebral cortical and hippocampal slices were incubated with [U-13C]glutamate and [U-13C]glutamine, and tissue extracts were analyzed by gas chromatography-mass spectrometry. The oxygen consumption rate using glutamate and glutamine as substrates was not different in isolated cerebral mitochondria of db/db mice compared to controls. Hippocampal slices of db/db mice exhibited significantly reduced 13C labeling in glutamate, glutamine, GABA, citrate, and aspartate from metabolism of [U-13C]glutamate. Additionally, reduced 13C labeling were observed in GABA, citrate, and aspartate from [U-13C]glutamine metabolism in hippocampal slices of db/db mice when compared to controls. None of these changes were observed in cerebral cortical slices. The results suggest specific hippocampal impairments in glutamate and glutamine metabolism, without affecting mitochondrial oxidation of these substrates, in the db/db mouse.
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Scaduto, R. C., and E. J. Davis. "Serine synthesis by an isolated perfused rat kidney preparation." Biochemical Journal 230, no. 2 (September 1, 1985): 303–11. http://dx.doi.org/10.1042/bj2300303.
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The isolated perfused rat kidney was shown to synthesize serine from aspartate or glutamate, both of which are also precursors of glucose. The major products of aspartate metabolism were ammonia, serine, glutamate, glucose, glutamine and CO2. Perfusion of kidneys with aspartate in the presence of amino-oxyacetate resulted in a near-complete inhibition of aspartate metabolism, illustrating the essential role of aspartate aminotransferase in the metabolism of this substrate. Radioactivity from 14C-labelled aspartate and from 14C-labelled glycerol was incorporated into serine and glucose. Production of both glucose and serine from aspartate was suppressed in the presence of 3-mercaptopicolinic acid. These data provide evidence for the operation of the phosphorylated and/or non-phosphorylated pathway for serine production to the presence of 3-mercaptopicolinic acid. This is explained by simultaneous glycolysis. The rate of glucose production, but not that of serine, was greater in kidneys perfused with glutamate or with aspartate plus glycerol than the rates obtained by perfusion with aspartate alone. These data are taken to suggest that serine synthesis occurred at a near-maximal rate, and that the capacity of the kidney for serine synthesis from glucose precursors is lower than that for glucose synthesis.
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Boasson, Rosalinda, and Michael Shaw. "The effects of glutamine, citrate, and pH on the growth and sporulation of Melampsora lini in axenic culture." Canadian Journal of Botany 66, no. 6 (June 1, 1988): 1230–36. http://dx.doi.org/10.1139/b88-175.
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Growth (protein) and sporulation (extinction at 458 nm) of uredial cultures of races 3 and 210 of flax rust were compared on axenic media containing cysteine plus either high (42 mM) aspartate or glutamate or high (42 mM) or low (4 mM) glutamine as the major source of amino N. On high aspartate, growth of race 210 was 2 times and sporulation 20 times that of race 3. Glutamate substituted for aspartate, but there was no growth on high glutamine unless cultures were first seeded and held on glutamate during an incubation period of 15 days. Growth on low glutamine was poor at pH 5.0. Increased pH or the addition of citrate overcame the inhibitory effect of low pH. Both races grew equally well on low glutamine at pH 5.5 or 6.0, with or without citrate, but growth of race 3 was only one-third to one-half that of race 210 on high aspartate. Sporulation of race 210 on low glutamine under these conditions was 4–5 times that of race 3, being as high as or higher than on aspartate. [14C(U)]Citrate was more rapidly metabolized at pH 5.0 than at 5.5 or 6.0. Evidence is presented that citrate promotes growth on low glutamine at pH 5.0 primarily because it prevents the rapid downward drift in pH that occurs in its absence and that periodic upward adjustment of the pH results in striking increases in sporulation.
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Sahai, A., I. Nissim, and R. L. Tannen. "Pathways of acute pH regulation of ammoniagenesis in LLC-PK1 cells: study with [15N]glutamine." American Journal of Physiology-Renal Physiology 261, no. 3 (September 1, 1991): F481—F487. http://dx.doi.org/10.1152/ajprenal.1991.261.3.f481.
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The present study utilized [15N]glutamine labeled at amide (5-N) and amino (2-N) groups to analyze the metabolic fate of glutamine nitrogen in basal and in acute pH regulation of ammoniagenesis. One-hour incubation of LLC-PK1 cultures in a media of pH 7.4, 7.0, or 7.6 containing either [5–15N]glutamine or [2–15N]glutamine resulted in parallel alterations in glutamine consumption in response to acute acid-base maneuvers. Incubation with [5–15N]glutamine resulted in substantial enrichment and production of ammonia at pH 7.4, which was unaffected by the changes in media pH, and in no significant enrichment of alanine, aspartate, and glutamate. In contrast, significant enrichment and production of 15N-labeled ammonia, alanine, aspartate, and glutamate were detected from cultures incubated with [2–15N]glutamine. Ammonia formation, from incubation with [2–15N]glutamine, was stimulated significantly by a low pH and inhibited by high pH. Alanine production was altered in a fashion similar to ammonia formation, whereas aspartate production was unaltered and glutamate formation significantly decreased by a low pH. Furthermore, a low pH significantly increased the production of alpha-ketoglutaramate in a fashion qualitatively similar to alanine production. In contrast to our prior conclusions based on total metabolite production, these studies indicate that although ammonia formation at pH 7.4 is predominantly generated from the mitochondrial phosphate-dependent glutaminase pathway, the increased ammonia formation in acute acidosis is a result of increased flux through glutamate dehydrogenase.(ABSTRACT TRUNCATED AT 250 WORDS)
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Welbourne, T. C., and X. Mu. "Extracellular glutamate flux regulates intracellular glutaminase activity in LLC-PK1-F+ cells." American Journal of Physiology-Cell Physiology 268, no. 6 (June 1, 1995): C1418—C1424. http://dx.doi.org/10.1152/ajpcell.1995.268.6.c1418.
Full textAbstract:
The role of extracellular glutamate flux in regulating intracellular glutaminase activity was assessed in confluent monolayers of proximal tubule-like LLC-PK1-F+ cells grown on porous supports. Glutamate is a well-known inhibitor of phosphate-dependent glutaminase (PDG). We hypothesized that, by restricting the flux of glutamate from the extracellular media, cellular level would fall, effecting deinhibition of the cellular glutaminase activity. To test this, cellular glutamate uptake and extracellular production were inhibited for 18 h by the addition of D-aspartate (10 mM) or acivicin (0.7 mM) to both apical and basal media. Inhibiting glutamate flux depressed cellular glutamate content 43 and 41%, respectively. Intracellular relative glutaminase activity, monitored as the breakdown of 14C-radiolabeled glutamine to glutamate, measured over 60 s in the presence of D-aspartate or acivicin showed a 2- to 2.5-fold increase with the fall in cellular glutamate. Interestingly, enhanced glutamine uptake after PDG deinhibition was predominantly expressed on the basal surface. Indeed, measuring glutamine utilization after gamma-glutamyltranspeptidase inhibition over the entire 18-h time course revealed inhibition at the apical surface but relative enhancement of uptake at the basal surface. The increased intracellular glutaminase pathway was also reflected in increased alanine production measured over the 18-h time course, despite the reduction in overall glutamine utilization. These results point to a major role for extracellular glutamate fluxes in regulating cellular glutamine metabolism and suggest that the intracellular pathway may be suppressed under these conditions.
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Lin, Yan, Mary C. Stephenson, Lijing Xin, Antonio Napolitano, and Peter G. Morris. "Investigating the Metabolic Changes due to Visual Stimulation using Functional Proton Magnetic Resonance Spectroscopy at 7 T." Journal of Cerebral Blood Flow & Metabolism 32, no. 8 (March 21, 2012): 1484–95. http://dx.doi.org/10.1038/jcbfm.2012.33.
Full textAbstract:
Proton magnetic resonance spectroscopy (1H-MRS) has been used to demonstrate metabolic changes in the visual cortex on visual stimulation. Small (2% to 11%) but significant stimulation induced increases in lactate, glutamate, and glutathione were observed along with decreases in aspartate, glutamine, and glycine, using 1H-MRS at 7 T during single and repeated visual stimulation. In addition, decreases in glucose and increases in γ-aminobutyric acid (GABA) were seen but did not reach significance. Changes in glutamate and aspartate are indicative of increased activity of the malate–aspartate shuttle, which taken together with the opposite changes in glucose and lactate, reflect the expected increase in brain energy metabolism. These results are in agreement with those of Mangia et al. In addition, increases in glutamate and GABA coupled with the decrease in glutamine can be interpreted in terms of increased activity of the neurotransmitter cycles. An entirely new observation is the increase of glutathione during prolonged visual stimuli. The similarity of its time course to that of glutamate suggests that it may be a response to the increased release of glutamate or to the increased production of reactive oxygen species. Together, these observations constitute the most detailed analysis to date of functional changes in human brain metabolites.
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Brand, K. "Glutamine and glucose metabolism during thymocyte proliferation. Pathways of glutamine and glutamate metabolism." Biochemical Journal 228, no. 2 (June 1, 1985): 353–61. http://dx.doi.org/10.1042/bj2280353.
Full textAbstract:
Energy metabolism in proliferating cultured rat thymocytes was compared with that of freshly prepared non-proliferating resting cells. Cultured rat thymocytes enter a proliferative cycle after stimulation by concanavalin A and Lymphocult T (interleukin-2), with maximal rates of DNA synthesis at 60 h. Compared with incubated resting thymocytes, glucose metabolism by incubated proliferating thymocytes was 53-fold increased; 90% of the amount of glucose utilized was converted into lactate, whereas resting cells metabolized only 56% to lactate. However, the latter oxidized 27% of glucose to CO2, as opposed to 1.1% by the proliferating cells. Activities of hexokinase, 6-phosphofructokinase, pyruvate kinase and aldolase in proliferating thymocytes were increased 12-, 17-, 30- and 24-fold respectively, whereas the rate of pyruvate oxidation was enhanced only 3-fold. The relatively low capacity of pyruvate degradation in proliferating thymocytes might be the reason for almost complete conversion of glucose into lactate by these cells. Glutamine utilization by rat thymocytes was 8-fold increased during proliferation. The major end products of glutamine metabolism are glutamate, aspartate, CO2 and ammonia. A complete recovery of glutamine carbon and nitrogen in the products was obtained. The amount of glutamate formed by phosphate-dependent glutaminase which entered the citric acid cycle was enhanced 5-fold in the proliferating cells: 76% was converted into 2-oxoglutarate by aspartate aminotransferase, present in high activity, and the remaining 24% by glutamate dehydrogenase. With resting cells the same percentages were obtained (75 and 25). Maximal activities of glutaminase, glutamate dehydrogenase and aspartate aminotransferase were increased 3-, 12- and 6-fold respectively in proliferating cells; 32% of the glutamate metabolized in the citric acid cycle was recovered in CO2 and 61% in aspartate. In resting cells this proportion was 41% and 59% and in mitogen-stimulated cells 39% and 65% respectively. Addition of glucose (4 mM) or malate (2 mM) strongly decreased the rates of glutamine utilization and glutamate conversion into 2-oxoglutarate by proliferating thymocytes and also affected the pathways of further glutamate metabolism. Addition of 2 mM-pyruvate did not alter the rate of glutamine utilization by proliferating thymocytes, but decreased the rate of metabolism beyond the stage of glutamate significantly. Formation of acetyl-CoA in the presence of pyruvate might explain the relatively enhanced oxidation of glutamate to CO2 (56%) by proliferating thymocytes.
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Wu, G., C. J. Field, and E. B. Marliss. "Elevated glutamine metabolism in splenocytes from spontaneously diabetic BB rats." Biochemical Journal 274, no. 1 (February 15, 1991): 49–54. http://dx.doi.org/10.1042/bj2740049.
Full textAbstract:
To investigate the metabolic fates of glutamine in splenocytes from the BB rat with spontaneous immunologically mediated insulin-dependent diabetes, freshly isolated cells were incubated in Krebs-Ringer Hepes buffer with 1.0 mM-[U-14C]glutamine and 0, 4 mM- or 15 mM-glucose. (1) The major products of glutamine metabolism in splenocytes from normal and diabetic rats were ammonia, glutamate, aspartate and CO2. (2) The addition of glucose increased (P less than 0.01) glutamate production, but decreased (P less than 0.01) aspartate and CO2 production from glutamine, as compared with the values obtained in the absence of glucose. However, there were no differences in these metabolites of glutamine at 4 mM- and 15 mM-glucose. (3) At all glucose concentrations used, the productions of ammonia, glutamate, aspartate and CO2 from glutamine were all markedly increased (P less than 0.01) in splenocytes from diabetic rats. (4) Potential ATP production from glutamine in the splenocytes was similar to that from glucose, and was increased in cells from the diabetic rat. (5) ATP concentrations were increased (P less than 0.01) in diabetic-rat splenocytes in the presence of glutamine with or without glucose. (6) Our results demonstrate that glutamine is an important energy substrate for splenocytes and suggest that the increased glutamine metabolism may be associated with the activation of certain subsets of splenocytes in the immunologically mediated diabetic syndrome.
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Hoeltzli, S. D., L. K. Kelley, A. J. Moe, and C. H. Smith. "Anionic amino acid transport systems in isolated basal plasma membrane of human placenta." American Journal of Physiology-Cell Physiology 259, no. 1 (July 1, 1990): C47—C55. http://dx.doi.org/10.1152/ajpcell.1990.259.1.c47.
Full textAbstract:
The placenta absorbs anionic amino acids from the maternal and fetal circulations but does not significantly transfer these amino acids from mother to fetus. Uptake of L-aspartate and L-glutamate by basal (fetal-facing) plasma membrane vesicles from placental syncytiotrophoblast was stimulated by an inward sodium and an outward potassium gradient. Measurable saturable uptake was entirely sodium dependent and electrogenic. Studies of concentration dependence resolved a high-affinity (microM) system that has characteristics of the X-AG system found in other tissues including the placental microvillous plasma membrane. Uptake of 0.2 microM L-glutamate was inhibited by 2 mM L-glutamate, L-aspartate, D-aspartate, L-cysteate, and L-cysteinesulfinic acid and was uninhibited by 2 mM D-glutamate, L-glutamine, L-alanine, L-serine, L-asparagine, and taurine or by 1 mM methylaminoisobutyric acid. The X-AG system in the two membranes of the placental syncytiotrophoblast may mediate the concentrative uptake of anionic amino acids from the maternal and fetal circulations into the placenta.
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Pangalos, M. N., A. L. Malizia, P. T. Francis, S. L. Lowe, P. H. F. Bertolucci, A. W. Procter, P. K. Bridges, J. R. Bartlett, and D. M. Bowen. "Effect of Psychotropic Drugs on Excitatory Amino Acids in Patients Undergoing Psychosurgery for Depression." British Journal of Psychiatry 160, no. 5 (May 1992): 638–42. http://dx.doi.org/10.1192/bjp.160.5.638.
Full textAbstract:
Samples of ventricular CSF were taken from 52 consecutive patients admitted for psychosurgery for intractable depression. Concentrations of asparagine, aspartate, glutamine, glutamic acid, and serine were determined. Glutamate and aspartate concentrations, implicated in excitotoxic brain damage, were not affected by various types of psychotropic drug treatment. Serine, a modulator of glutamate responses, was significantly elevated in samples from subjects receiving antidepressants. These subjects responded poorly to the operation. Psychotropic drugs are unlikely to be neurotoxic. Nevertheless, antidepressants may influence excitatory neurotransmission.
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Grant, George B., and Frank S. Werblin. "A glutamate-elicited chloride current with transporter-like properties in rod photoreceptors of the tiger salamander." Visual Neuroscience 13, no. 1 (January 1996): 135–44. http://dx.doi.org/10.1017/s0952523800007185.
Full textAbstract:
AbstractGlutamate, when puffed near the synaptic terminals, elicits a current in rod photoreceptors. The current is strongly dependent upon both the intracellular and extracellular chloride concentration: its reversal potential follows the predicted Nernst potential for a chloride permeable channel. The glutamate-elicited current also requires the presence of extracellular sodium. This glutamate-elicited current is pharmacologically like a glutamate transporter: it is elicited, in order of efficacy, by L-glutamate, L-aspartate, L-cysteate, D-aspartate, and D-glutamate, all shown to activate glutamate transport in other systems. Furthermore, it is reduced by the glutamate transport antagonists dihydrokainate (DHKA) and D, L-threo-3–hydroxyaspartate (THA). THA, when applied alone, elicits a current similar to that elicited by glutamate. The current cannot be activated by the glutamate receptor agonists kainate, quisqualate, NMDA and APB, nor can it be blocked by the glutamale receptor antagonists CNQX and APV. Thus, the current does not appear to be mediated by a conventional glutamate receptor. Taken together, the ionic dependence and pharmacology of this current suggest that it is generated by glutamate transporter coupled to a chloride channel.
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Nilsson, G. E., and S. Winberg. "Changes in the brain levels of GABA and related amino acids in anoxic shore crab (Carcinus maenas)." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 264, no. 4 (April 1, 1993): R733—R737. http://dx.doi.org/10.1152/ajpregu.1993.264.4.r733.
Full textAbstract:
The effects of anoxia on the brain concentrations of gamma-aminobutyric acid (GABA), glutamate, aspartate, glutamine, alanine, and taurine were measured in the shore crab (Carcinus maenas) and compared with data previously obtained from anoxia-tolerant vertebrates. C. maenas was found to survive 12 h in nitrogen-bubbled water. The changes found in brain amino acid levels were strikingly similar to those seen in anoxia-tolerant vertebrates. Thus, during anoxia, the brain of C. maenas displayed considerable increases in the concentrations of GABA (2.4-fold increase after 12 h) and alanine (8-fold increase after 12 h). By contrast, the brain levels of glutamate, aspartate, and glutamine fell significantly during anoxia, whereas the taurine level remained unchanged. Because GABA is a major inhibitory neurotransmitter in arthropods (as well as in most animal phyla), it is suggested that the increased level of GABA could promote the anoxic metabolic depression displayed by C. maenas and thus prolong anoxic survival. It is also possible that the decreases in glutamate and aspartate levels could play similar roles.
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Beitz, A. J. "Relationship of glutamate and aspartate to the periaqueductal gray-raphe magnus projection: analysis using immunocytochemistry and microdialysis." Journal of Histochemistry & Cytochemistry 38, no. 12 (December 1990): 1755–65. http://dx.doi.org/10.1177/38.12.1701457.
Full textAbstract:
This study tested the hypothesis that the excitatory amino acid transmitters glutamate and/or aspartate are associated with the periaqueductal gray (PAG)-raphe magnus (NRM) projection. Retrograde neuroanatomical tracing procedures utilizing the tracers WGA-HRP or D-[3H]-aspartate were combined with immunocytochemical localization of glutamate or aspartate to determine if glutamate and/or aspartate immunostained neurons projected to the NRM. Both glutamate- and aspartate-immunoreactive cells in the PAG were found to project to the NRM. Double labeling immunocytochemichemical procedures indicated that glutamate and aspartate are co-localized in many PAG neurons, suggesting the following possibilities: (a) one of these two amino acids may serve as a precursor to the other; (b) both amino acids may be co-released from the same PAG neuron; or (c) both amino acids are present in high levels in the perikarya for metabolic purposes. At the EM level, both glutamate- and aspartate-immunoreactive terminals were identified in the NRM, strengthening the concept that both amino acids participate in synaptic transmission in this medullary nucleus. To determine if glutamate and aspartate are in fact released from PAG-NRM axons, the PAG was stimulated chemically with homocysteic acid (HCA) and amino acids were collected from the NRM using a microdialysis probe. Microinjection of HCA, but not vehicle, into the PAG resulted in the release of both glutamate and aspartate in the nucleus raphe magnus. These data suggest that both glutamate and aspartate are released from PAG fibers terminating in the NRM and provide strong support for the hypothesis that excitatory amino acids play a neurotransmitter role in the PAG-NRM pathway.
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Wu, Guoyao, Catherine J. Field, and Errol B. Marliss. "Glutamine and glucose metabolism in thymocytes from normal and spontaneously diabetic BB rats." Biochemistry and Cell Biology 69, no. 12 (December 1, 1991): 801–8. http://dx.doi.org/10.1139/o91-120.
Full textAbstract:
Metabolism of glutamine and glucose was studied in thymocytes from normal rats and BB rats with the spontaneous autoimmune diabetic syndrome to assess their potential roles as fuels. The major measured products from glucose were lactate and, to a lesser extent, CO2, and pyruvate. Glutamine had no effect on the rates of their production from glucose. Glutamine was metabolized to ammonia, aspartate, glutamate, and CO2, with aspartate being the major product of carbons from glutamine in the absence of glucose. Glucose markedly decreased the formation of ammonia, aspartate, and CO2 from glutamine, but increased that of glutamate, with an overall decrease in glutamine utilization by 55%. More glutamate than aspartate was produced from glutamine in the presence of glucose. The potential production of ATP from glucose was similar to that when glutamine was present alone. However, glucose markedly decreased production of ATP from glutamine, but not vice versa. This resulted in ATP production from glucose being 2.5 times that from glutamine when both substrates were present. The oxidation of glucose to CO2 via the Krebs cycle accounts for 75–80% of glucose-derived ATP production. Cellular ATP levels markedly decreased in the absence of exogenous substrates, but were constant throughout a 2-h incubation in the presence of glutamine, glucose, or both. There were no differences in thymocyte glucose or glutamine metabolism between normal and diabetic BB rats, in contrast to previous findings in peripheral lymphoid organs. Our results suggest that glucose is a more important fuel than glutamine for "resting" thymocytes, again in contrast to the cells of peripheral lymphoid organs in which glutamine is as important as glucose as a fuel. The enhanced energy metabolism found in the cells from peripheral lymphoid organs of diabetic BB rats, if due to T-lymphocytes, must occur after their migration out of the thymus.Key words: glutaminolysis, glycolysis, thymocytes, ATP, BB rats.
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Bloomfield, S. A., and J. E. Dowling. "Roles of aspartate and glutamate in synaptic transmission in rabbit retina. I. Outer plexiform layer." Journal of Neurophysiology 53, no. 3 (March 1, 1985): 699–713. http://dx.doi.org/10.1152/jn.1985.53.3.699.
Full textAbstract:
Intracellular recordings were obtained from horizontal and bipolar cells of the superfused, isolated retina-eyecup of the rabbit. The putative neurotransmitters aspartate, glutamate, and several analogues were added to the superfusate while the membrane potential and light-responsiveness of the retinal neurons were monitored. Both L-aspartate and L-glutamate mimicked the actions of the endogenous photoreceptor transmitter on horizontal cells, on-bipolar cells, and off-bipolar cells. At applied concentrations of 2.5-20 mM, the actions of L-aspartate and L-glutamate were indistinguishable. D-aspartate potentiated the effects of both L-aspartate and L-glutamate on horizontal cells. This suggests that active uptake systems for these amino acids exist in the outer plexiform layer (OPL) of the rabbit retina. The glutamate analogue kainate produced effects similar to those of aspartate and glutamate on second-order neurons, but at concentrations lower by over two orders of magnitude. The glutamate analogue quisqualate had effects similar to kainate but with much less potency. The aspartate analogue n-methyl DL-aspartate (NMDLA) antagonized the effects of the photoreceptor transmitter on horizontal and off-bipolar cells. This action of NMDLA was only observed at low concentrations (50 microM). In addition, NMDLA could block the effects of exogenously applied kainate. The NMDLA had no clear effects on on-bipolar cells. The glutamate analogue 2-amino-4-phosphonobutyrate reversibly blocked the responses of on-bipolar cells but had no effect on either horizontal or off-bipolar cell responses. This suggests that on-bipolar cells possess a unique synaptic receptor. The aspartate analogue 2-amino-3-phosphonoproprionate did not show this selectivity, suggesting that this unique receptor is a glutamate-preferring receptor. The antagonists alpha-methyl glutamate, alpha-amino adipate, and glutamate diethyl ester all showed only a weak ability to antagonize the actions of the photoreceptor transmitter on second-order neurons. The results of this study indicate that glutamate or a glutamate-like substance is the likely transmitter of rods and cones in the rabbit retina. A comparison of the present findings with those previously obtained in lower vertebrate retinas suggests that the basic pharmacological design of the OPL of all vertebrate retinas is very similar.
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Ollenschläger, G., K. Langer, H. M. Steffen, M. Schrappe-Bächer, H. Schmitt, B. Allolio, and E. Roth. "Intracellular free amino acid patterns in duodenal and colonic mucosa." Clinical Chemistry 36, no. 2 (February 1, 1990): 378–81. http://dx.doi.org/10.1093/clinchem/36.2.378.
Full textAbstract:
Abstract We report for the first time the concentrations of free amino acids in human intestinal biopsies obtained by routinely performed endoscopy. We studied 15 medical patients with no changes of the mucosa and six HIV-infected persons with duodenitis. The mean (and SD) sum of all amino acids, taurine excepted, was 61.9 (5.4) mmol/kg dry weight in duodenal biopsies of HIV-negative subjects (n = 11) and 82.9 (0.6) mmol/kg in colonic specimens: 50% (44%) of the total (minus taurine) consisted of aspartate and glutamate and 14% (12%), of the essential amino acids. The relative amino acid pattern in duodenum and colon differed completely from that for muscle: aspartate was fourfold higher; glutamate, phenylalanine, glycine, valine, leucine, and isoleucine were about twofold higher. In contrast, glutamine amounted only to 4% (duodenum) to 14% (colon) of muscle glutamine. In duodenal biopsies of the HIV-infected persons, we found significantly (P less than 0.01, except glutamine: P less than 0.025) increased concentrations of glutamate (24.1 vs 17 mmol/kg dry weight), ornithine (1.4 vs 0.4), valine (2.2 vs 1.7), and glutamine.
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Ta, Trung Chanh, and Kenneth W. Joy. "Transamination, deamidation, and the utilisation of asparagine amino nitrogen in pea leaves." Canadian Journal of Botany 63, no. 5 (May 1, 1985): 881–84. http://dx.doi.org/10.1139/b85-115.
Full textAbstract:
The fate of 15N from the amino group of labelled asparagine was followed in growing pea leaves, in the presence and absence of inhibitors of deamidation (DONV, 5-diazo-4-oxo-L-norvaline) and transamination (AOA, aminooxyacetate). The label was widely incorporated into various amino acids, especially aspartate, glutamate, alanine, and homoserine, as well as glycine and serine. Treatment with AOA considerably decreased the label of all these amino acids except aspartate, consistent with the production of the latter by deamidation of asparagine. This was confirmed by the use of DONV, which decreased aspartate labelling by over 70%; a similar decrease in glutamate labelling suggested that the latter was labelled predominantly by transamination of aspartate. In contrast, DONV had a much smaller effect on the labelling of alanine, homoserine, glycine, and serine, indicating a direct transfer of amino nitrogen from asparagine, rather than transfer from aspartate (or glutamate). The labelling of glycine and serine and the transfer of amino nitrogen to ammonia and glutamine (amide group) were consistent with a flow of asparagine nitrogen into the photorespiratory nitrogen cycle. During leaf expansion there was a decrease in the amount of asparagine metabolised, and a decreasing participation of deamidation as the leaf matured.
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Wakabayashi, Maki, Toshio Hasegawa, Takuji Yamaguchi, Naoko Funakushi, Hajime Suto, Rie Ueki, Hiroyuki Kobayashi, Hideoki Ogawa, and Shigaku Ikeda. "Yokukansan, a Traditional Japanese Medicine, Adjusts Glutamate Signaling in Cultured Keratinocytes." BioMed Research International 2014 (2014): 1–7. http://dx.doi.org/10.1155/2014/364092.
Full textAbstract:
Glutamate plays an important role in skin barrier signaling. In our previous study, Yokukansan (YKS) affected glutamate receptors in NC/Nga mice and was ameliorated in atopic dermatitis lesions. The aim of this study was to assess the effect of YKS on skin and cultured human keratinocytes. Glutamate concentrations in skin of YKS-treated and nontreated NC/Nga mice were measured. Then, glutamate release from cultured keratinocytes was measured, and extracellular glutamate concentrations in YKS-stimulated cultured human keratinocytes were determined. The mRNA expression levels of NMDA receptor 2D (NMDAR2D) and glutamate aspartate transporter (GLAST) were also determined in YKS-stimulated cultured keratinocytes. The glutamate concentrations and dermatitis scores increased in conventional mice, whereas they decreased in YKS-treated mice. Glutamate concentrations in cell supernatants of cultured keratinocytes increased proportionally to the cell density. However, they decreased dose-dependently with YKS. YKS stimulation increased NMDAR2D in a concentration-dependent manner. Conversely, GLAST decreased in response to YKS. Our findings indicate that YKS affects peripheral glutamate signaling in keratinocytes. Glutamine is essential as a transmitter, and dermatitis lesions might produce and release excess glutamate. This study suggests that, in keratinocytes, YKS controls extracellular glutamate concentrations, suppresses N-methyl-D-aspartate (NMDA) receptors, and activates glutamate transport.
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Phend, K. D., R. J. Weinberg, and A. Rustioni. "Techniques to optimize post-embedding single and double staining for amino acid neurotransmitters." Journal of Histochemistry & Cytochemistry 40, no. 7 (July 1992): 1011–20. http://dx.doi.org/10.1177/40.7.1376741.
Full textAbstract:
We report a number of technical refinements for single and double staining with post-embedding electron microscopy for glutamate, aspartate, and gamma-aminobutyric acid. Best results were obtained with 2.5% glutaraldehyde in the fixative and by minimizing the duration of plastic polymerization and the interval between cutting and reacting. Quantitative documentation of the ability of exogenous glutamate, aspartate, and gamma-aminobutyric acid to block their immune staining is provided. Increased intensity of staining with the glutamate and aspartate antisera resulted from preincubation of glutamate antiserum with aspartate and aspartate antiserum with glutamate. To perform double staining with antisera raised in the same species, it was necessary to block antigenicity of the first antiserum; best results were obtained with hot paraformaldehyde fumes. By using a detergent instead of etching, these methods permitted the simultaneous visualization of tracers to identify neuroanatomic pathways.
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Ta, T. C., F. D. H. Macdowall, M. A. Faris, and K. W. Joy. "Metabolism of nitrogen fixed by root nodules of alfalfa (Medicago sativa L.): I. Utilization of [14C, 15N]glutamate and [14C, 15N]glutamine in the synthesis of γ-aminobutyrate." Biochemistry and Cell Biology 66, no. 12 (December 1, 1988): 1342–48. http://dx.doi.org/10.1139/o88-155.
Full textAbstract:
The fate of nitrogen and carbon from [14C, 15N]glutamate and glutamine, two primary assimilation products of ammonia from fixed nitrogen, was studied by vacuum infiltration of the compounds into alfalfa nodule slices. The amide group of glutamine is an important precursor in the synthesis of asparagine, a major transport compound in alfalfa; this reaction, catalyzed by asparagine synthetase, also produces glutamate. Glutamate is also synthesized by the action of glutamate synthase. Transamination plays an important role in the redistribution of the nitrogen groups to yield a range of amino acids. The rapid transfer of 15N from glutamate to aspartate provides the substrate for asparagine synthesis. Some glutamate was used in glutamine synthesis, indicating the operation of glutamine synthetase. Glutamate is also metabolized by decarboxylation to γ-aminobutyric acid (Gaba), a nonprotein amino acid abundant in alfalfa nodules; Gaba is further metabolized by transamination. Considerable amounts of carbon from both glutamine and glutamate enter the pool of organic acids and are utilized in the synthesis of amino acids. There is relatively little metabolism of glutamate by isolated bacteroids.
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Melø, Torun M., Astrid Nehlig, and Ursula Sonnewald. "Metabolism is Normal in Astrocytes in Chronically Epileptic Rats: A 13C NMR Study of Neuronal—Glial Interactions in a Model of Temporal Lobe Epilepsy." Journal of Cerebral Blood Flow & Metabolism 25, no. 10 (May 18, 2005): 1254–64. http://dx.doi.org/10.1038/sj.jcbfm.9600128.
Full textAbstract:
The aim of the present work was to study potential disturbances in metabolism and interactions between neurons and glia in the lithium-pilocarpine model of temporal lobe epilepsy. Rats chronically epileptic for 1 month received [1-13C]glucose, a substrate for neurons and astrocytes, and [1,2-13C]acetate, a substrate for astrocytes only. Analyses of extracts from cerebral cortex, cerebellum, and hippocampal formation (hippocampus, amygdala, entorhinal, and piriform cortices) were performed using 13C and 1H nuclear magnetic resonance spectroscopy and HPLC. In the hippocampal formation of epileptic rats, levels of glutamate, aspartate, N-acetyl aspartate, adenosine triphosphate plus adenosine diphosphate and glutathione were decreased. In all regions studied, labeling from [1,2-13C]acetate was similar in control and epileptic rats, indicating normal astrocytic metabolism. However, labeling of glutamate, GABA, aspartate, and alanine from [1-13C]glucose was decreased in all areas possibly reflecting neuronal loss. The labeling of glutamine from [1-13C]glucose was decreased in cerebral cortex and cerebellum and unchanged in hippocampal formation. In conclusion, no changes were detected in glial—neuronal interactions in the hippocampal formation while in cortex and cerebellum the flow of glutamate to astrocytes was decreased, indicating a disturbed glutamate—glutamine cycle. This is, to our knowledge, the first study showing that metabolic disturbances are confined to neurons inside the epileptic circuit.
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Carter, P., and T. Welbourne. "Glutamate transport regulation of renal glutaminase flux in vivo." American Journal of Physiology-Endocrinology and Metabolism 273, no. 3 (September 1997): E521. http://dx.doi.org/10.1152/ajpendo.1997.273.3.e521.
Full textAbstract:
We proposed that glutamate transport into cultured kidney cells represses cellular glutaminase activity and hence regulates glutamine utilization. To test this putative regulatory mechanism in vivo, glutamine uptake and conversion to glutamate as well as ammonium production were measured in the intact functioning rat kidney. Glutamine uptake was determined as net removal, arteriovenous concentration difference times renal plasma flow, and also as unidirectional uptake from the fractional extraction of tracer L-[14C]glutamine. Ammonium production was measured as that released into the renal vein plus that excreted, and intracellular glutamine conversion to glutamate was assessed from the rise in cortical glutamate radiolabel specific activity. Cellular glutamate content was reduced 50-60% by infusing D-aspartate (a high-affinity glutamate transporter inhibitor) over 30 min, consistent with interdiction of glutamate uptake. This reduction in the glutaminase repressor was associated with a three- to fivefold increase in glutamine uptake and intracellular conversion to glutamate and ammonium. These results are consistent with and predictable from our previous in vitro model and point to an important role for this regulatory mechanism in the intact functioning organ.
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Nissim, I., M. Yudkoff, and S. Segal. "Metabolic fate of glutamate carbon in rat renal tubules. Studies with 13C nuclear magnetic resonance and gas chromatography-mass spectrometry." Biochemical Journal 241, no. 2 (January 15, 1987): 361–70. http://dx.doi.org/10.1042/bj2410361.
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13C-n.m.r. spectroscopy and g.c.-m.s. were used to determine the metabolic fate of glutamate carbon in rat kidney. The main purpose was to characterize the effect of chronic metabolic acidosis on the utilization of glutamate carbon. Renal tubules obtained from normal and chronically acidotic rats were incubated in Krebs buffer, pH 7.4, in the presence of 2.5 mM-[3-13C]glutamate. During the course of incubation the concentrations of total glucose and NH3 were significantly (P less than 0.05) higher in tissue from acidotic rats. The levels of some tricarboxylic-acid-cycle intermediates were higher (P less than 0.05) in control tissue. In control tissue, 13C-n.m.r. spectra demonstrated a significantly higher rate of 13C appearance of aspartate, glutamine and [2,4-13C]glutamate. However, in acidosis the resonances of [13C]glucose carbon atoms were significantly higher. In the control, approx. 15% of glutamate carbon was accounted for by [13C]glucose formation as against 30% in chronic acidosis. However, in control tissue, 44% of glutamate carbon utilization was accounted for by recycling to glutamate and formation of aspartate, glutamine and GABA. In acidosis, only 11% was so recovered. Analysis of 15NH3 formation during the course of incubation with 2.5 mM-[15N]glutamate demonstrated a positive association between the appearance of [13C]glucose and 15NH3 both in the control and in acidosis. The data suggest that the control of gluconeogenesis and ammoniagenesis in acidosis is, in part, referable to a diminution in the rate of the reductive amination of alpha-oxoglutarate, that of the transamination reaction and that of glutamine synthesis.
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Hsu, Chin, Jau-Nan Lee, Mei-Ling Ho, Bi-Hwa Cheng, Pi-Hseuh Shirley Li, and John Yuh-Lin Yu. "The facilitatory effect of N-methyl-D-aspartate on sexual receptivity in female rats through GnRH release." Acta Endocrinologica 128, no. 4 (April 1993): 385–88. http://dx.doi.org/10.1530/acta.0.1280385.
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The purpose of this study was to examine whether N-methyl-D-aspartate affects the sexual receptivity of female rats. Monosodium L-glutamate was used as a neurotoxin to induce hypogonadal status. Matured normal and monosodium L-glutamate-treated rats were ovariectomized and implanted subcutaneously with estradiol capsules. One week later, lordosis responsiveness was observed before and 10 min after N-methyl-D-aspartate (40 mg/kg of BW, ip) administration. The results showed that N-methyl-D-aspartate caused a remarkable increase of lordosis quotient in control rats but not in monosodium L-glutamate-treated rats. Moreover, the possible action site of N-methyl-D-aspartate in the enhancement of receptivity was evaluated by the post-castrational LH rise, pituitary LH release in response to GnRH, and N-methyl-D-aspartate-evoked GnRH releasability. The results revealed that: (a) serum levels of LH in monosodium L-glutamate-treated rats were lower (p <0.01) than those of control rats after ovariectomy; (b) there was no significant difference of pituitary LH release responsiveness to GnRH test between two groups; and (c) N-methyl-D-aspartate-evoked LH release in monosodium L-glutamate-treated rats was similar to that in the control rats. In conclusion, N-methyl-D-aspartate may facilitate the sexual receptivity through stimulating GnRH release. The failure of N-methyl-D-aspartate in enhancing receptivity in monosodium L-glutamate-treated rats is probably due to the cellular damage by monosodium L-glutamate on specific areas responsible for lordosis.
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Ni, Hengjia, Lu Lu, Jinpin Deng, Wenjun Fan, Tiejun Li, and Jiming Yao. "Effects of Glutamate and Aspartate on Serum Antioxidative Enzyme, Sex Hormones, and Genital Inflammation in Boars Challenged with Hydrogen Peroxide." Mediators of Inflammation 2016 (2016): 1–10. http://dx.doi.org/10.1155/2016/4394695.
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Background. Oxidative stress is associated with infertility. This study was conducted to determine the effects of glutamate and aspartate on serum antioxidative enzymes, sex hormones, and genital inflammation in boars suffering from oxidative stress.Methods. Boars were randomly divided into 4 groups: the nonchallenged control (CON) and H2O2-challenged control (BD) groups were fed a basal diet supplemented with 2% alanine; the other two groups were fed the basal diet supplemented with 2% glutamate (GLU) or 2% aspartate (ASP). The BD, GLU, and ASP groups were injected with hydrogen peroxide (H2O2) on day 15. The CON group was injected with 0.9% sodium chloride solution on the same day.Results. Dietary aspartate decreased the malondialdehyde (MDA) level in serum (P<0.05) compared with the BD group. Additionally, aspartate maintained serum luteinizing hormone (LH) at a relatively stable level. Moreover, glutamate and aspartate increased transforming growth factor-β1 (TGF-β1) and interleukin-10 (IL-10) levels in the epididymis and testis (P<0.05) compared with the BD group.Conclusion. Both glutamate and aspartate promoted genital mRNA expressions of anti-inflammatory factors after oxidative stress. Aspartate more effectively decreased serum MDA and prevented fluctuations in serum sex hormones after H2O2challenge than did glutamate.
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Argilés, J. M., and F. J. López-Soriano. "The effects of tumour necrosis factor-α (cachectin) and tumour growth on hepatic amino acid utilization in the rat." Biochemical Journal 266, no. 1 (February 15, 1990): 123–26. http://dx.doi.org/10.1042/bj2660123.
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The effects of acute administration of tumour necrosis factor-alpha (cachectin) (TNF-alpha) or of malignant tumour growth (Walker-256 carcinosarcoma) on hepatic availability and uptake of individual amino acids were compared. The results show that, in spite of lowering the hepatic availability of alanine, aspartate, serine, glycine and proline, the cytokine increased both the total amino acid hepatic uptake and the individual uptakes of alanine, glutamate, serine, threonine, proline, lysine and arginine, while decreasing those of leucine, isoleucine and phenylalanine. Tumour burden resulted in an increase in the hepatic availability of glutamine, threonine, glycine, lysine, leucine, isoleucine, valine and phenylalanine. Total liver amino acid uptake was unaffected, whereas the individual uptakes of alanine, threonine and proline were increased and those of glutamate, glutamine, serine and leucine were decreased. When effects of the cytokine are compared with those induced by tumour growth, there are similar increases in net utilization for alanine, proline and leucine, and a 3-fold difference in the increase observed for threonine. Unmatched effects are seen for glutamate, glutamine, aspartate, glycine, lysine, arginine, valine, phenylalanine and serine.
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Wakayama, Mamoru, Kazue Takashima, Yuko Tau, Sadatoshi Nakashima, Kenji Sakai, and Mitsuaki Moriguchi. "Spectrophotometric Assay ofd-Aspartate andd-Glutamate Usingd-Aspartate Oxidase with Malate Dehydrogenase and Glutamate Dehydrogenase." Analytical Biochemistry 250, no. 2 (August 1997): 252–53. http://dx.doi.org/10.1006/abio.1997.2230.
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Jung, K., M. Pergande, R. Rej, G. Schreiber, and W. Schimmelpfennig. "Mitochondrial enzymes in human serum: comparative determinations of glutamate dehydrogenase and mitochondrial aspartate aminotransferase in healthy persons and patients with chronic liver diseases." Clinical Chemistry 31, no. 2 (February 1, 1985): 239–43. http://dx.doi.org/10.1093/clinchem/31.2.239.
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Abstract We measured the activities of two mitochondrial enzymes, the mitochondrial form of aspartate aminotransferase (EC 2.6.1.1) and glutamate dehydrogenase (EC 1.4.1.2), in the serum of apparently healthy persons (n = 84) and patients suffering from chronic liver diseases (n = 43). The distribution of activities for glutamate dehydrogenase, but not mitochondrial aspartate aminotransferase, was sex-dependent. The upper limits of the reference intervals (99th percentile) at 37 degrees C were 3.2 U/L for mitochondrial aspartate aminotransferase, 6.4 U/L for glutamate dehydrogenase (women), and 11.0 U/L for glutamate dehydrogenase (men); there was a weak correlation between the activities of both mitochondrial enzymes (r = 0.439). In patients with chronic liver diseases we found a greater increase in the activity of glutamate dehydrogenase than of mitochondrial aspartate aminotransferase and the correlation between the two mitochondrial enzymes was stronger. The diagnostic sensitivity and specificity of either mitochondrial enzyme was less than that of total aspartate aminotransferase, alanine aminotransferase (EC 2.6.1.2), or gamma-glutamyltransferase (EC 2.3.2.2).
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Bender, Katrin, Pierre Maechler, Neville H. McClenaghan, Peter R. Flatt, and Philip Newsholme. "Overexpression of the malate–aspartate NADH shuttle member Aralar1 in the clonal β-cell line BRIN-BD11 enhances amino-acid-stimulated insulin secretion and cell metabolism." Clinical Science 117, no. 9 (September 1, 2009): 321–30. http://dx.doi.org/10.1042/cs20090126.
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In the present study, we have investigated the effects of the transduction with recombinant adenovirus AdCA-Aralar1 (aspartate–glutamate carrier 1) on the metabolism, function and secretory properties of the glucose- and amino-acid-responsive clonal insulin-secreting cell line BRIN-BD11. Aralar1 overexpression increased long-term (24 h) and acute (20 min) glucose- and amino-acid-stimulated insulin secretion, cellular glucose metabolism, L-alanine and L-glutamine consumption, cellular ATP and glutamate concentrations, and stimulated glutamate release. However, cellular triacylglycerol and glycogen contents were decreased as was lactate production. These findings indicate that increased malate–aspartate shuttle activity positively shifted β-cell metabolism, thereby increasing glycolysis capacity, stimulus–secretion coupling and, ultimately, enhancing insulin secretion. We conclude that Aralar1 is a key metabolic control site in insulin-secreting cells.
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Welbourne, Tomas, and Itzhak Nissim. "Regulation of mitochondrial glutamine/glutamate metabolism by glutamate transport: studies with 15N." American Journal of Physiology-Cell Physiology 280, no. 5 (May 1, 2001): C1151—C1159. http://dx.doi.org/10.1152/ajpcell.2001.280.5.c1151.
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We focused on the role of plasma membrane glutamate uptake in modulating the intracellular glutaminase (GA) and glutamate dehydrogenase (GDH) flux and in determining the fate of the intracellular glutamate in the proximal tubule-like LLC-PK1-F+ cell line. We used high-affinity glutamate transport inhibitors d-aspartate (d-Asp) and dl-threo-β-hydroxyaspartate (THA) to block extracellular uptake and then used [15N]glutamate or [2-15N]glutamine to follow the metabolic fate and distribution of glutamine and glutamate. In monolayers incubated with [2-15N]glutamine (99 atom %excess), glutamine and glutamate equilibrated throughout the intra- and extracellular compartments. In the presence of 5 mMd-Asp and 0.5 mM THA, glutamine distribution remained unchanged, but the intracellular glutamate enrichment decreased by 33% ( P < 0.05) as the extracellular enrichment increased by 39% ( P < 0.005). With glutamate uptake blocked, intracellular glutamate concentration decreased by 37% ( P < 0.0001), in contrast to intracellular glutamine concentration, which remained unchanged. Both glutamine disappearance from the media and the estimated intracellular GA flux increased with the fall in the intracellular glutamate concentration. The labeled glutamate and NH[Formula: see text] formed from [2-15N]glutamine and recovered in the media increased 12- and 3-fold, respectively, consistent with accelerated GA and GDH flux. However, labeled alanine formation was reduced by 37%, indicating inhibition of transamination. Although both d-Asp and THA alone accelerated the GA and GDH flux, only THA inhibited transamination. These results are consistent with glutamate transport both regulating and being regulated by glutamine and glutamate metabolism in epithelial cells.
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Herbst, Eric A. F., and Graham P. Holloway. "Exercise increases mitochondrial glutamate oxidation in the mouse cerebral cortex." Applied Physiology, Nutrition, and Metabolism 41, no. 7 (July 2016): 799–801. http://dx.doi.org/10.1139/apnm-2016-0033.
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The present study investigated the impact of acute exercise on stimulating mitochondrial respiratory function in mouse cerebral cortex. Where pyruvate-stimulated respiration was not affected by acute exercise, glutamate respiration was enhanced following the exercise bout. Additional assessment revealed that this affect was dependent on the presence of malate and did not occur when substituting glutamine for glutamate. As such, our results suggest that glutamate oxidation is enhanced with acute exercise through activation of the malate–aspartate shuttle.
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Jung, Y. G., T. Sakata, E. S. Lee, and Y. Fukui. "Amino acid metabolism of bovine blastocysts derived from parthenogenetically activated or in vitro fertilized oocytes." Reproduction, Fertility and Development 10, no. 3 (1998): 279. http://dx.doi.org/10.1071/r98052.
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The uptake and synthesis of 19 amino acids by fresh or frozen–thawed bovine blastocysts produced by parthenogenesis (PT) or in vitro fertilization (IVF) were compared in the present study. Fresh blastocysts, 180 h after IVF or PT activation, and frozen–thawed blastocysts, 168 h old and cultured for 12 h post-thawing, were cultured in synthetic oviduct fluid medium (SOFM) containing polyvinyl alcohol (PVA) with both essential and non-essential amino acids (EAA and NEAA, respectively) (Medium 1: M1) or SOFM containing PVA with only EAA (Medium 2: M2). In Experiment 1, when fresh or frozen–thawed PT blastocysts were cultured in M1, the uptake of glutamate (in fresh only), aspartate and arginine, and the synthesis of glutamine and alanine were significantly enhanced. In the culture with M2, serine, asparagine, glutamate, glutamine, glycine, arginine and alanine were significantly taken up. It was found that the glutamine concentrations was significantly higher (P < 0.001) in the culture medium drops containing embryos than in the drops without embryos. In Experiment 2, when PT blastocysts were cultured in M1, the uptake of aspartate and synthesis of alanine were greater (P < 0.01) than those by IVF blastocysts. When M2 was used, a significant (P < 0.01) production of serine, asparagine, glutamate, glutamine and alanine, and the uptake of arginine by PT blastocysts were observed. In Experiment 3, when IVF blastocysts were cultured in M1, fresh blastocysts depleted more aspartate and glutamate, and produced more glutamine and alanine than frozen–thawed blastocysts. When cultured in M2, frozen–thawed blastocysts depleted more threonine (P < 0.01) than fresh blastocysts. These results indicate that the uptake and synthesis of amino acids were different in fresh or frozen–thawed bovine blastocysts derived from PT or IVF. These differences in amino acid metabolism may be related to the viability of the blastocysts.
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Bloomfield, S. A., and J. E. Dowling. "Roles of aspartate and glutamate in synaptic transmission in rabbit retina. II. Inner plexiform layer." Journal of Neurophysiology 53, no. 3 (March 1, 1985): 714–25. http://dx.doi.org/10.1152/jn.1985.53.3.714.
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Intracellular recordings were obtained from amacrine and ganglion cells in the superfused, isolated retina-eyecup of the rabbit. The putative neurotransmitters aspartate, glutamate, and several of their analogues were added to the superfusate while the membrane potential and light-responsiveness of the retinal neurons were monitored. Both L-aspartate and L-glutamate displayed excitatory actions on the activity of the vast majority of amacrine and ganglion cells studied. However, these agents occasionally appeared to inhibit the responses of the inner retinal neurons by producing hyperpolarization of the membrane potential and blockage of the light-evoked responses. In either case, the effects of aspartate and glutamate were indistinguishable. The glutamate analogues kainate and quisqualate produced strong excitatory effects on the responses of amacrine and ganglion cells at concentrations some 200-fold less than those needed to obtain similar effects with aspartate or glutamate. The aspartate analogue, n-methyl DL-aspartate (NMDLA), also produced strong excitatory effects but was approximately three times less potent than kainate or quisqualate. On one occasion, we encountered a ganglion cell that was depolarized by kainate, but hyperpolarized by NMDLA. The glutamate antagonist alpha-methyl glutamate and the aspartate antagonist alpha-amino adipate effectively blocked the responses of amacrine and ganglion cells. However, on any one cell, one antagonist was always clearly more potent than the other. We examined the actions of the glutamate analogue 2-amino-4-phosphonobutyrate (APB) on the responses of inner retinal neurons and found that it selectively abolished all "on" activity in the inner retina. Together with our finding that APB selectively abolishes on-bipolar cell responses (see Ref. 6), these data support the hypothesis that on-bipolar cells subserve the "on" activity of amacrine and ganglion cells. Our data suggest that aspartate and glutamate are excitatory transmitters in the inner retina, possibly being released from bipolar cell axon terminals in the inner plexiform layer.
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Zheng, Su, and Robert Haselkorn. "A glutamate/glutamine/aspartate/asparagine transport operon in Rhodobacter capsulatus." Molecular Microbiology 20, no. 5 (June 1996): 1001–11. http://dx.doi.org/10.1111/j.1365-2958.1996.tb02541.x.
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FERNÁNDEZ-PASCUAL, Sergio, André MUKALA-NSENGU-TSHIBANGU, Rafael MARTÍN del RÍO, and Jorge TAMARIT-RODRÍGUEZ. "Conversion into GABA (gamma-aminobutyric acid) may reduce the capacity of l-glutamine as an insulin secretagogue." Biochemical Journal 379, no. 3 (May 1, 2004): 721–29. http://dx.doi.org/10.1042/bj20031826.
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We have carried out a detailed examination of l-glutamine metabolism in rat islets in order to elucidate the paradoxical failure of l-glutamine to stimulate insulin secretion. l-Glutamine was converted by isolated islets into GABA (γ-aminobutyric acid), l-aspartate and l-glutamate. Saturation of the intracellular concentrations of all of these amino acids occurred at approx. 10 mmol/l l-glutamine, and their half-maximal values were attained at progressively increasing concentrations of l-glutamine (0.3 mmol/l for GABA; 0.5 and 1.0 mmol/l for Asp and Glu respectively). GABA accumulation accounted for most of the 14CO2 produced at various l-[U-14C]glutamine concentrations. Potentiation by l-glutamine of l-leucine-induced insulin secretion in perifused islets was suppressed by malonic acid dimethyl ester, was accompanied by a significant decrease in islet GABA accumulation, and was not modified in the presence of GABA receptor antagonists [50 µmol/l saclofen or 10 µmol/l (+)-bicuculline]. l-Leucine activated islet glutamate dehydrogenase activity, but had no effect on either glutamate decarboxylase or GABA transaminase activity, in islet homogenates. We conclude that (i) l-glutamine is metabolized preferentially to GABA and l-aspartate, which accumulate in islets, thus preventing its complete oxidation in the Krebs cycle, which accounts for its failure to stimulate insulin secretion; (ii) potentiation by l-glutamine of l-leucine-induced insulin secretion involves increased metabolism of l-glutamate and GABA via the Krebs cycle (glutamate dehydrogenase activation) and the GABA shunt (2-oxoglutarate availability for GABA transaminase) respectively, and (iii) islet release of GABA does not seem to play an important role in the modulation of the islet secretory response to the combination of l-leucine and l-glutamine.