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1
Ferrandi, Erica Elisa, Ivan Bassanini, Susanna Bertuletti, Sergio Riva, Chiara Tognoli, Marta Vanoni e Daniela Monti. "Functional Characterization and Synthetic Application of Is2-SDR, a Novel Thermostable and Promiscuous Ketoreductase from a Hot Spring Metagenome". International Journal of Molecular Sciences 23, n. 20 (12 ottobre 2022): 12153. http://dx.doi.org/10.3390/ijms232012153.
Testo completoAbstract (sommario):
In a metagenome mining-based search of novel thermostable hydroxysteroid dehydrogenases (HSDHs), enzymes that are able to selectively oxidize/reduce steroidal compounds, a novel short-chain dehydrogenase/reductase (SDR), named Is2-SDR, was recently discovered. This enzyme, found in an Icelandic hot spring metagenome, shared a high sequence similarity with HSDHs, but, unexpectedly, showed no activity in the oxidation of the tested steroid substrates, e.g., cholic acid. Despite that, Is2-SDR proved to be a very active and versatile ketoreductase, being able to regio- and stereoselectively reduce a diversified panel of carbonylic substrates, including bulky ketones, α- and β-ketoesters, and α-diketones of pharmaceutical relevance. Further investigations showed that Is2-SDR was indeed active in the regio- and stereoselective reduction of oxidized steroid derivatives, and this outcome was rationalized by docking analysis in the active site model. Moreover, Is2-SDR showed remarkable thermostability, with an apparent melting temperature (TM) around 75 °C, as determined by circular dichroism analysis, and no significant decrease in catalytic activity, even after 5 h at 80 °C. A broad tolerance to both water-miscible and water-immiscible organic solvents was demonstrated as well, thus, confirming the potential of this new biocatalyst for its synthetic application.
2
Mineo, Chieko, Yun-Shu Ying, Christine Chapline, Susan Jaken e Richard G. W. Anderson. "Targeting of Protein Kinase Cα to Caveolae". Journal of Cell Biology 141, n. 3 (4 maggio 1998): 601–10. http://dx.doi.org/10.1083/jcb.141.3.601.
Testo completoAbstract (sommario):
Previously, we showed caveolae contain a population of protein kinase Cα (PKCα) that appears to regulate membrane invagination. We now report that multiple PKC isoenzymes are enriched in caveolae of unstimulated fibroblasts. To understand the mechanism of PKC targeting, we prepared caveolae lacking PKCα and measured the interaction of recombinant PKCα with these membranes. PKCα bound with high affinity and specificity to caveolae membranes. Binding was calcium dependent, did not require the addition of factors that activate the enzyme, and involved the regulatory domain of the molecule. A 68-kD PKCα-binding protein identified as sdr (serum deprivation response) was isolated by interaction cloning and localized to caveolae. Antibodies against sdr inhibited PKCα binding. A 100–amino acid sequence from the middle of sdr competitively blocked PKCα binding while flanking sequences were inactive. Caveolae appear to be a membrane site where PKC enzymes are organized to carry out essential regulatory functions as well as to modulate signal transduction at the cell surface.
3
Cassetta, Alberto, Ivet Krastanova, Katja Kristan, Mojca Brunskole Švegelj, Doriano Lamba, Tea Lanišnik Rižner e Jure Stojan. "Insights into subtle conformational differences in the substrate-binding loop of fungal 17β-hydroxysteroid dehydrogenase: a combined structural and kinetic approach". Biochemical Journal 441, n. 1 (14 dicembre 2011): 151–60. http://dx.doi.org/10.1042/bj20110567.
Testo completoAbstract (sommario):
The 17β-HSD (17β-hydroxysteroid dehydrogenase) from the filamentous fungus Cochliobolus lunatus (17β-HSDcl) is a NADP(H)-dependent enzyme that preferentially catalyses the interconversion of inactive 17-oxo-steroids and their active 17β-hydroxy counterparts. 17β-HSDcl belongs to the SDR (short-chain dehydrogenase/reductase) superfamily. It is currently the only fungal 17β-HSD member that has been described and represents one of the model enzymes of the cP1 classical subfamily of NADPH-dependent SDR enzymes. A thorough crystallographic analysis has been performed to better understand the structural aspects of this subfamily and provide insights into the evolution of the HSD enzymes. The crystal structures of the 17β-HSDcl apo, holo and coumestrol-inhibited ternary complex, and the active-site Y167F mutant reveal subtle conformational differences in the substrate-binding loop that probably modulate the catalytic activity of 17β-HSDcl. Coumestrol, a plant-derived non-steroidal compound with oestrogenic activity, inhibits 17β-HSDcl [IC50 2.8 μM; at 100 μM substrate (4-oestrene-3,17-dione)] by occupying the putative steroid-binding site. In addition to an extensive hydrogen-bonding network, coumestrol binding is stabilized further by π–π stacking interactions with Tyr212. A stopped-flow kinetic experiment clearly showed the coenzyme dissociation as the slowest step of the reaction and, in addition to the low steroid solubility, it prevents the accumulation of enzyme–coenzyme–steroid ternary complexes.
4
FRANSEN, Marc, Paul P. VAN VELDHOVEN e Suresh SUBRAMANI. "Identification of peroxisomal proteins by using M13 phage protein VI phage display: molecular evidence that mammalian peroxisomes contain a 2,4-dienoyl-CoA reductase". Biochemical Journal 340, n. 2 (25 maggio 1999): 561–68. http://dx.doi.org/10.1042/bj3400561.
Testo completoAbstract (sommario):
To elucidate unknown mammalian peroxisomal enzymes and functions, we subjected M13 phage expressing fusions between the gene encoding protein VI and a rat liver cDNA library to an immunoaffinity selection process in vitro (biopanning) with the use of antibodies raised against peroxisomal subfractions. In an initial series of biopanning experiments, four different cDNA clones were obtained. These cDNA species encoded two previously identified peroxisomal enzymes, catalase and urate oxidase, and two novel proteins that contained a C-terminal peroxisomal targeting signal (PTS1). A primary structure analysis of these novel proteins revealed that one, ending in the tripeptide AKL, is homologous to the yeast peroxisomal 2,4-dienoyl-CoA reductase (EC 1.3.1.34; DCR), an enzyme required for the degradation of unsaturated fatty acids, and that the other, ending in the tripeptide SRL, is a putative member of the short-chain dehydrogenase/reductase (SDR) family, with three isoforms. Green fluorescent protein (GFP) fusions encoding GFP-DCR-AKL, GFP-DCR, GFP-SDR-SRL and GFP-SDR were expressed in mammalian cells. The analysis of the subcellular location of the recombinant fusion proteins confirmed the peroxisomal localization of GFP-DCR-AKL and GFP-SDR-SRL, as well as the functionality of the PTS1. That the AKL protein is indeed an NADPH-dependent DCR was demonstrated by showing DCR activity of the bacterially expressed protein. These results demonstrate at the molecular level that mammalian peroxisomes do indeed contain a DCR. In addition, the results presented here indicate that the protein VI display system is suitable for the isolation of rare cDNA clones from cDNA libraries and that this technology facilitates the identification of novel peroxisomal proteins.
5
Nguyen, Giang Thu, Shinae Kim, Hyeonseok Jin, Dong-Hyung Cho, Hang-Suk Chun, Woo-Keun Kim e Jeong Ho Chang. "Crystal Structure of NADPH-Dependent Methylglyoxal Reductase Gre2 from Candida Albicans". Crystals 9, n. 9 (10 settembre 2019): 471. http://dx.doi.org/10.3390/cryst9090471.
Testo completoAbstract (sommario):
Gre2 is a key enzyme in the methylglyoxal detoxification pathway; it uses NADPH or NADH as an electron donor to reduce the cytotoxic methylglyoxal to lactaldehyde. This enzyme is a member of the short-chain dehydrogenase/reductase (SDR) superfamily whose members catalyze this type of reaction with a broad range of substrates. To elucidate the structural features, we determined the crystal structures of the NADPH-dependent methylglyoxal reductase Gre2 from Candida albicans (CaGre2) for both the apo-form and NADPH-complexed form at resolutions of 2.8 and 3.02 Å, respectively. The CaGre2 structure is composed of two distinct domains: the N-terminal cofactor-binding domain and the C-terminal substrate-binding domain. Extensive comparison of CaGre2 with its homologous structures reveals conformational changes in α12 and β3′ of the NADPH-complex forms. This study may provide insights into the structural and functional variation of SDR family proteins.
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Pampa, Kudigana J., Neratur K. Lokanath, Naoki Kunishima e Ravishankar Vittal Rai. "The first crystal structure of NAD-dependent 3-dehydro-2-deoxy-D-gluconate dehydrogenase fromThermus thermophilusHB8". Acta Crystallographica Section D Biological Crystallography 70, n. 4 (19 marzo 2014): 994–1004. http://dx.doi.org/10.1107/s1399004713034925.
Testo completoAbstract (sommario):
2-Keto-3-deoxygluconate (KDG) is one of the important intermediates in pectin metabolism. An enzyme involved in this pathway, 3-dehydro-3-deoxy-D-gluconate 5-dehydrogenase (DDGDH), has been identified which converts 2,5-diketo-3-deoxygluconate to KDG. The enzyme is a member of the short-chain dehydrogenase (SDR) family. To gain insight into the function of this enzyme at the molecular level, the first crystal structure of DDGDH fromThermus thermophilusHB8 has been determined in the apo form, as well as in complexes with the cofactor and with citrate, by X-ray diffraction methods. The crystal structures reveal a tight tetrameric oligomerization. The secondary-structural elements and catalytically important residues of the enzyme were highly conserved amongst the proteins of the NAD(P)-dependent SDR family. The DDGDH protomer contains a dinucleotide-binding fold which binds the coenzyme NAD+in an intersubunit cleft; hence, the observed oligomeric state might be important for the catalytic function. This enzyme prefers NAD(H) rather than NADP(H) as the physiological cofactor. A structural comparison of DDGDH with mouse lung carbonyl reductase suggests that a significant difference in the α–loop–α region of this enzyme is associated with the coenzyme specificity. The structural data allow a detailed understanding of the functional role of the conserved catalytic triad (Ser129–Tyr144–Lys148) in cofactor and substrate recognition, thus providing substantial insights into DDGDH catalysis. From analysis of the three-dimensional structure, intersubunit hydrophobic interactions were found to be important for enzyme oligomerization and thermostability.
7
Prasad, Kailash. "Importance of Flaxseed and its Components in the Management of Hypertension". International Journal of Angiology 28, n. 03 (22 febbraio 2019): 153–60. http://dx.doi.org/10.1055/s-0039-1678691.
Testo completoAbstract (sommario):
AbstractThis review paper describes the effects of flaxseed and its components (flax oil, secoisolariciresinol diglucoside [SDG], flax lignan complex [FLC], and flaxseed protein hydrolysate [FPH]) on blood pressure (BP) in Sprague Dawley rats (SDR), spontaneously hypertensive rats (SHR), and humans. Flaxseed, flax oil, and FLC had variable effects on BP in humans, while SDG and FPH significantly reduced the BP in SDR and SHR. The effect of SDG was dose-dependent and long lasting. The lowering of BP is mediated through inhibition of soluble epoxide by α-linolenic acid in flax oil, stimulation of guanylate cyclase and inhibition of angiotensin converting enzyme (ACE) by SDG, and inhibition of renin and ACE activity by FPH. Flaxseed, flax oil, and FLC have variable effects on BP (none, slight, and significant). They are effective in lowering BP in individuals with hypertension and metabolic syndrome but ineffective in healthy individuals' ineffectiveness of flaxseed and its compounds in lowering BP may be due to their low doses, long interval of dosing, short duration of consumption, and patient status. In conclusion, the data at present suggest that flaxseed, flax oil, and FLC cannot serve as therapeutic agents for the treatment of hypertension. However, they can be used as an adjunct in the treatment of hypertension. A clinical trial should be conducted of these agents with higher doses which would be given twice daily for long duration. Pure SDG and FPS may serve as therapeutic agents for the treatment of hypertension but they have not been tried in humans.
8
Da Costa, Matthieu, Ophelia Gevaert, Stevie Van Overtveldt, Joanna Lange, Henk-Jan Joosten, Tom Desmet e Koen Beerens. "Structure-function relationships in NDP-sugar active SDR enzymes: Fingerprints for functional annotation and enzyme engineering". Biotechnology Advances 48 (maggio 2021): 107705. http://dx.doi.org/10.1016/j.biotechadv.2021.107705.
Testo completo
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Shah, Bhumika S., Sasha G. Tetu, Stephen J. Harrop, Ian T. Paulsen e Bridget C. Mabbutt. "Structure of a short-chain dehydrogenase/reductase (SDR) within a genomic island from a clinical strain ofAcinetobacter baumannii". Acta Crystallographica Section F Structural Biology Communications 70, n. 10 (25 settembre 2014): 1318–23. http://dx.doi.org/10.1107/s2053230x14019785.
Testo completoAbstract (sommario):
Over 15% of the genome of an Australian clinical isolate ofAcinetobacter baumanniioccurs within genomic islands. An uncharacterized protein encoded within one island feature common to this and other International Clone II strains has been studied by X-ray crystallography. The 2.4 Å resolution structure of SDR-WM99c reveals it to be a new member of the classical short-chain dehydrogenase/reductase (SDR) superfamily. The enzyme contains a nucleotide-binding domain and, like many other SDRs, is tetrameric in form. The active site contains a catalytic tetrad (Asn117, Ser146, Tyr159 and Lys163) and water molecules occupying the presumed NADP cofactor-binding pocket. An adjacent cleft is capped by a relatively mobile helical subdomain, which is well positioned to control substrate access.
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van Hylckama Vlieg, Johan E. T., Lixia Tang, Jeffrey H. Lutje Spelberg, Tim Smilda, Gerrit J. Poelarends, Tjibbe Bosma, Annet E. J. van Merode, Marco W. Fraaije e Dick B. Janssen. "Halohydrin Dehalogenases Are Structurally and Mechanistically Related to Short-Chain Dehydrogenases/Reductases". Journal of Bacteriology 183, n. 17 (1 settembre 2001): 5058–66. http://dx.doi.org/10.1128/jb.183.17.5058-5066.2001.
Testo completoAbstract (sommario):
ABSTRACT Halohydrin dehalogenases, also known as haloalcohol dehalogenases or halohydrin hydrogen-halide lyases, catalyze the nucleophilic displacement of a halogen by a vicinal hydroxyl function in halohydrins to yield epoxides. Three novel bacterial genes encoding halohydrin dehalogenases were cloned and expressed in Escherichia coli, and the enzymes were shown to display remarkable differences in substrate specificity. The halohydrin dehalogenase ofAgrobacterium radiobacter strain AD1, designated HheC, was purified to homogeneity. The k cat andK m values of this 28-kDa protein with 1,3-dichloro-2-propanol were 37 s−1 and 0.010 mM, respectively. A sequence homology search as well as secondary and tertiary structure predictions indicated that the halohydrin dehalogenases are structurally similar to proteins belonging to the family of short-chain dehydrogenases/reductases (SDRs). Moreover, catalytically important serine and tyrosine residues that are highly conserved in the SDR family are also present in HheC and other halohydrin dehalogenases. The third essential catalytic residue in the SDR family, a lysine, is replaced by an arginine in halohydrin dehalogenases. A site-directed mutagenesis study, with HheC as a model enzyme, supports a mechanism for halohydrin dehalogenases in which the conserved Tyr145 acts as a catalytic base and Ser132 is involved in substrate binding. The primary role of Arg149 may be lowering of the pKa of Tyr145, which abstracts a proton from the substrate hydroxyl group to increase its nucleophilicity for displacement of the neighboring halide. The proposed mechanism is fundamentally different from that of the well-studied hydrolytic dehalogenases, since it does not involve a covalent enzyme-substrate intermediate.
11
Yao, Juan, Zhang Zhang, Zhenghua Deng, Youqiang Wang e Yongcan Guo. "An enzyme free electrochemical biosensor for sensitive detection of miRNA with a high discrimination factor by coupling the strand displacement reaction and catalytic hairpin assembly recycling". Analyst 142, n. 21 (2017): 4116–23. http://dx.doi.org/10.1039/c7an01224a.
Testo completo
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Pennacchio, Angela, Biagio Pucci, Francesco Secundo, Francesco La Cara, Mosè Rossi e Carlo A. Raia. "Purification and Characterization of a Novel Recombinant Highly Enantioselective Short-Chain NAD(H)-Dependent Alcohol Dehydrogenase from Thermus thermophilus". Applied and Environmental Microbiology 74, n. 13 (2 maggio 2008): 3949–58. http://dx.doi.org/10.1128/aem.00217-08.
Testo completoAbstract (sommario):
ABSTRACT The gene encoding a novel alcohol dehydrogenase (ADH) that belongs to the short-chain dehydrogenase/reductase (SDR) superfamily was identified in the extremely thermophilic, halotolerant gram-negative eubacterium Thermus thermophilus HB27. The T. thermophilus ADH gene (adh Tt) was heterologously overexpressed in Escherichia coli, and the protein (ADHTt) was purified to homogeneity and characterized. ADHTt is a tetrameric enzyme consisting of identical 26,961-Da subunits composed of 256 amino acids. The enzyme has remarkable thermophilicity and thermal stability, displaying activity at temperatures up to ∼73°C and a 30-min half-inactivation temperature of ∼90°C, as well as good tolerance to common organic solvents. ADHTt has a strict requirement for NAD(H) as the coenzyme, a preference for reduction of aromatic ketones and α-keto esters, and poor activity on aromatic alcohols and aldehydes. This thermophilic enzyme catalyzes the following reactions with Prelog specificity: the reduction of acetophenone, 2,2,2-trifluoroacetophenone, α-tetralone, and α-methyl and α-ethyl benzoylformates to (S)-(−)-1-phenylethanol (>99% enantiomeric excess [ee]), (R)-α-(trifluoromethyl)benzyl alcohol (93% ee), (S)-α-tetralol (>99% ee), methyl (R)-(−)-mandelate (92% ee), and ethyl (R)-(−)-mandelate (95% ee), respectively, by way of an efficient in situ NADH-recycling system involving 2-propanol and a second thermophilic ADH. This study further supports the critical role of the D37 residue in discriminating NAD(H) from NADP(H) in members of the SDR superfamily.
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Janssen, D. B., M. Majerić-Elenkov, G. Hasnaoui, B. Hauer e J. H. Lutje Spelberg. "Enantioselective formation and ring-opening of epoxides catalysed by halohydrin dehalogenases". Biochemical Society Transactions 34, n. 2 (20 marzo 2006): 291–95. http://dx.doi.org/10.1042/bst0340291.
Testo completoAbstract (sommario):
Halohydrin dehalogenases catalyse the conversion of vicinal halohydrins into their corresponding epoxides, while releasing halide ions. They can be found in several bacteria that use halogenated alcohols or compounds that are degraded via halohydrins as a carbon source for growth. Biochemical and structural studies have shown that halohydrin dehalogenases are evolutionarily and mechanistically related to enzymes of the SDR (short-chain dehydrogenase/reductase) superfamily. In the reverse reaction, which is epoxide-ring opening, different nucleophiles can be accepted, including azide, nitrite and cyanide. This remarkable catalytic promiscuity allows the enzymatic production of a broad range of β-substituted alcohols from epoxides. In these oxirane-ring-opening reactions, the halohydrin dehalogenase from Agrobacterium radiobacter displays high enantioselectivity, making it possible to use the enzyme for the preparation of enantiopure building blocks for fine chemicals.
14
Theriault, Jean-Francois, Dao-Wei Zhu e Sheng-Xiang Lin. "The trans-membrane 17βHSD7: Kinetic study and preliminary crystallization data". Acta Crystallographica Section A Foundations and Advances 70, a1 (5 agosto 2014): C1503. http://dx.doi.org/10.1107/s2053273314084964.
Testo completoAbstract (sommario):
Human 17β-Hydroxysteroid dehydrogenase type 7 (h17HSD7) is a transmembrane enzyme belonging to the large, phylogenetically related protein family of short-chain dehydrogenases/reductases (SDR). In this study, h17HSD7 was expressed, purified, and the steady-state kinetics was studied. Here we report a purification method of the transmembrane enzyme using FPLC equipment with a combination of detergents to obtain homogeneous protein. We also report steady-state kinetics for h17HSD7 at 37 degrees Celsius and pH 7.5, using a homogeneous enzyme preparation with estrone (E1), or dihydrotestosterone (DHT) as substrate and NADPH as the cofactor. Kinetic studies made over a wide range of concentrations of both steroids (2microM to 60microM) revealed that E1 (Km= 12microM) has a higher apparent affinity for the h17BHSD7 compared to DHT (Km= 44microM). Crystallization of h17HSD7 in complex with high concentration of steroids to saturate the enzyme in the drop as low apparent affinity of both steroids was found in kinetic study. Some preliminary crystals were obtained by hanging-drop and diffracted at synchrotron facility (Maximum resolution: 2.95Å , Space group: H 3 2, Average unit cell: 120.74 120.74 201.94 90 90 90, Mosaicity : 0.51).
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Lee, Jung-Kul, Bong-Seong Koo, Sang-Yong Kim e Hyung-Hwan Hyun. "Purification and Characterization of a Novel Mannitol Dehydrogenase from a Newly Isolated Strain of Candida magnoliae". Applied and Environmental Microbiology 69, n. 8 (agosto 2003): 4438–47. http://dx.doi.org/10.1128/aem.69.8.4438-4447.2003.
Testo completoAbstract (sommario):
ABSTRACT Mannitol biosynthesis in Candida magnoliae HH-01 (KCCM-10252), a yeast strain that is currently used for the industrial production of mannitol, is catalyzed by mannitol dehydrogenase (MDH) (EC 1.1.1.138). In this study, NAD(P)H-dependent MDH was purified to homogeneity from C. magnoliae HH-01 by ion-exchange chromatography, hydrophobic interaction chromatography, and affinity chromatography. The relative molecular masses of C. magnoliae MDH, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and size-exclusion chromatography, were 35 and 142 kDa, respectively, indicating that the enzyme is a tetramer. This enzyme catalyzed both fructose reduction and mannitol oxidation. The pH and temperature optima for fructose reduction and mannitol oxidation were 7.5 and 37°C and 10.0 and 40°C, respectively. C. magnoliae MDH showed high substrate specificity and high catalytic efficiency (k cat = 823 s−1, K m = 28.0 mM, and k cat /K m = 29.4 mM−1 s−1) for fructose, which may explain the high mannitol production observed in this strain. Initial velocity and product inhibition studies suggest that the reaction proceeds via a sequential ordered Bi Bi mechanism, and C. magnoliae MDH is specific for transferring the 4-pro-S hydrogen of NADPH, which is typical of a short-chain dehydrogenase reductase (SDR). The internal amino acid sequences of C. magnoliae MDH showed a significant homology with SDRs from various sources, indicating that the C. magnoliae MDH is an NAD(P)H-dependent tetrameric SDR. Although MDHs have been purified and characterized from several other sources, C. magnoliae MDH is distinguished from other MDHs by its high substrate specificity and catalytic efficiency for fructose only, which makes C. magnoliae MDH the ideal choice for industrial applications, including enzymatic synthesis of mannitol and salt-tolerant plants.
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Kazakova, Oxana B., Natalya I. Medvedeva, Irina E. Smirnova, Tatyana V. Lopatina e Alexander V. Veselovsky. "The Introduction of Hydrazone, Hydrazide, or Azepane Moieties to the Triterpenoid Core Enhances an Activity Against M. tuberculosis". Medicinal Chemistry 17, n. 2 (30 dicembre 2020): 134–45. http://dx.doi.org/10.2174/1573406416666200115161700.
Testo completoAbstract (sommario):
Background: Triterpenoids exhibit a wide spectrum of antimicrobial activity. Objective: The objective of this study was to synthesize a series of nitrogen derivatives based on lupane, oleanane, and ursane triterpenoids with high antitubercular activity. Methods: Isonicotinoylhydrazones were prepared via the reaction of 3-oxotriterpenic acids or betulonic aldehyde with isoniazid (INH) in yields of 54-72%. N-Acylation of betulonic or azepanobetulinic acids led to lupane C28 hydrazides and dihydrazides. The derivatives were evaluated for their in vitro antimycobacterial activities against Mycobacterium tuberculosis (MTB) H37RV and single-drug resistance (SDR)-TB in the National Institute of Allergy and Infectious Diseases, USA. Molecular docking was performed to evaluate the possible binding modes of investigated compounds in the active site of Diterpene synthase (Rv3378c). Results: The obtained compounds are represented by C3 or C28 conjugates with hydrazine hydrate or INH. Some compounds demonstrated from high minimum inhibitory concentration (MIC ≤ 10 μg/mL) to excellent (MICs from 0.19 to 1.25 μg/mL) activity against MTB H37RV. Two lupane conjugates with INH were the leading compounds against MTB H37RV and some SDR-strains with MICs ranged from 0.19 to 1.70 μg/mL. Molecular docking of active compounds to diterpene synthase showed that these moieties accommodate the active site of the enzyme. Conclusions: It was revealed that the conjugation of lupanes with INH at C3 is more effective than at C28 and the lupane skeleton is preferable among oleanane and ursane types. The replacement of native hexacarbocyclic A ring to seven-member azepane ring is favorably for inhibition of both MTB H37RV and SDR-strains. These data could possibly mean that the antitubercular activity against INH-resistant strains (INH-R) came from both triterpenoid and isoniazid parts of the hybrid molecules. Azepanobetulin showed the highest activity against both INH-R strains in comparison with other triterpenoids and INH. Thus, the introduction of hydrazone, hydrazide (dihydrazide), or azepane moieties into the triterpenoid core is a promising way for the development of new anti-tubercular agents.
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Büsing, Imke, H. Wolfgang Höffken, Michael Breuer, Lars Wöhlbrand, Bernhard Hauer e Ralf Rabus. "Molecular Genetic and Crystal Structural Analysis of 1-(4-Hydroxyphenyl)-Ethanol Dehydrogenase from ‘Aromatoleum aromaticum' EbN1". Journal of Molecular Microbiology and Biotechnology 25, n. 5 (2015): 327–39. http://dx.doi.org/10.1159/000439113.
Testo completoAbstract (sommario):
The dehydrogenation of 1-(4-hydroxyphenyl)-ethanol to 4-hydroxyacetophenone represents the second reaction step during anaerobic degradation of <i>p</i>-ethylphenol in the denitrifying bacterium ‘<i>Aromatoleum aromaticum</i>' EbN1. Previous proteogenomic studies identified two different proteins (ChnA and EbA309) as possible candidates for catalyzing this reaction [Wöhlbrand et al: J Bacteriol 2008;190:5699-5709]. Physiological-molecular characterization of newly generated unmarked <i>in-frame</i> deletion and complementation mutants allowed defining ChnA (renamed here as Hped) as the enzyme responsible for 1-(4-hydroxyphenyl)-ethanol oxidation. Hped [1-(4-hydroxyphenyl)-ethanol dehydrogenase] belongs to the ‘classical' family within the short-chain alcohol dehydrogenase/reductase (SDR) superfamily. Hped was overproduced in <i>Escherichia coli</i>, purified and crystallized. The X-ray structures of the apo- and NAD<sup>+</sup>-soaked form were resolved at 1.5 and 1.1 Å, respectively, and revealed Hped as a typical homotetrameric SDR. Modeling of the substrate 4-hydroxyacetophenone (reductive direction of Hped) into the active site revealed the structural determinants of the strict <i>(R)</i>-specificity of Hped (Phe<sup>187</sup>), contrasting the <i>(S)</i>-specificity of previously reported 1-phenylethanol dehydrogenase (Ped; Tyr<sup>93</sup>) from strain EbN1 [Höffken et al: Biochemistry 2006;45:82-93].
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Lukacik, Petra, Brigitte Keller, Gabor Bunkoczi, Kathryn Kavanagh, Wen Hwa Lee, Jerzy Adamski e Udo Oppermann. "Structural and biochemical characterization of human orphan DHRS10 reveals a novel cytosolic enzyme with steroid dehydrogenase activity". Biochemical Journal 402, n. 3 (26 febbraio 2007): 419–27. http://dx.doi.org/10.1042/bj20061319.
Testo completoAbstract (sommario):
To this day, a significant proportion of the human genome remains devoid of functional characterization. In this study, we present evidence that the previously functionally uncharacterized product of the human DHRS10 gene is endowed with 17β-HSD (17β-hydroxysteroid dehydrogenase) activity. 17β-HSD enzymes are primarily involved in the metabolism of steroids at the C-17 position and also of other substrates such as fatty acids, prostaglandins and xenobiotics. In vitro, DHRS10 converts NAD+ into NADH in the presence of oestradiol, testosterone and 5-androstene-3β,17β-diol. Furthermore, the product of oestradiol oxidation, oestrone, was identified in intact cells transfected with a construct plasmid encoding the DHRS10 protein. In situ fluorescence hybridization studies have revealed the cytoplasmic localization of DHRS10. Along with tissue expression data, this suggests a role for DHRS10 in the local inactivation of steroids in the central nervous system and placenta. The crystal structure of the DHRS10 apoenzyme exhibits secondary structure of the SDR (short-chain dehydrogenase/reductase) family: a Rossmann-fold with variable loops surrounding the active site. It also reveals a broad and deep active site cleft into which NAD+ and oestradiol can be docked in a catalytically competent orientation.
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Rodarte, Justas V., Jan Abendroth, Thomas E. Edwards, Donald D. Lorimer, Bart L. Staker, Sunny Zhang, Peter J. Myler e Krystle J. McLaughlin. "Crystal structure of acetoacetyl-CoA reductase from Rickettsia felis". Acta Crystallographica Section F Structural Biology Communications 77, n. 2 (1 febbraio 2021): 54–60. http://dx.doi.org/10.1107/s2053230x21001497.
Testo completoAbstract (sommario):
Rickettsia felis, a Gram-negative bacterium that causes spotted fever, is of increasing interest as an emerging human pathogen. R. felis and several other Rickettsia strains are classed as National Institute of Allergy and Infectious Diseases priority pathogens. In recent years, R. felis has been shown to be adaptable to a wide range of hosts, and many fevers of unknown origin are now being attributed to this infectious agent. Here, the structure of acetoacetyl-CoA reductase from R. felis is reported at a resolution of 2.0 Å. While R. felis acetoacetyl-CoA reductase shares less than 50% sequence identity with its closest homologs, it adopts a fold common to other short-chain dehydrogenase/reductase (SDR) family members, such as the fatty-acid synthesis II enzyme FabG from the prominent pathogens Staphylococcus aureus and Bacillus anthracis. Continued characterization of the Rickettsia proteome may prove to be an effective means of finding new avenues of treatment through comparative structural studies.
20
Vögeli, Bastian, Raoul G. Rosenthal, Gabriele M. M. Stoffel, Tristan Wagner, Patrick Kiefer, Niña Socorro Cortina, Seigo Shima e Tobias J. Erb. "InhA, the enoyl-thioester reductase from Mycobacterium tuberculosis forms a covalent adduct during catalysis". Journal of Biological Chemistry 293, n. 44 (14 settembre 2018): 17200–17207. http://dx.doi.org/10.1074/jbc.ra118.005405.
Testo completoAbstract (sommario):
The enoyl-thioester reductase InhA catalyzes an essential step in fatty acid biosynthesis of Mycobacterium tuberculosis and is a key target of antituberculosis drugs to combat multidrug-resistant M. tuberculosis strains. This has prompted intense interest in the mechanism and intermediates of the InhA reaction. Here, using enzyme mutagenesis, NMR, stopped-flow spectroscopy, and LC–MS, we found that the NADH cofactor and the CoA thioester substrate form a covalent adduct during the InhA catalytic cycle. We used the isolated adduct as a molecular probe to directly access the second half-reaction of the catalytic cycle of InhA (i.e. the proton transfer), independently of the first half-reaction (i.e. the initial hydride transfer) and to assign functions to two conserved active-site residues, Tyr-158 and Thr-196. We found that Tyr-158 is required for the stereospecificity of protonation and that Thr-196 is partially involved in hydride transfer and protonation. The natural tendency of InhA to form a covalent C2-ene adduct calls for a careful reconsideration of the enzyme's reaction mechanism. It also provides the basis for the development of effective tools to study, manipulate, and inhibit the catalytic cycle of InhA and related enzymes of the short-chain dehydrogenase/reductase (SDR) superfamily. In summary, our work has uncovered the formation of a covalent adduct during the InhA catalytic cycle and identified critical residues required for catalysis, providing further insights into the InhA reaction mechanism important for the development of antituberculosis drugs.
21
Oppermann, Udo C. T., Samina Salim, Lars O. Tjernberg, Lars Terenius e Hans Jörnvall. "Binding of amyloid β-peptide to mitochondrial hydroxyacyl-CoA dehydrogenase (ERAB): regulation of an SDR enzyme activity with implications for apoptosis in Alzheimer's disease". FEBS Letters 451, n. 3 (28 maggio 1999): 238–42. http://dx.doi.org/10.1016/s0014-5793(99)00586-4.
Testo completo
22
Zhang, Hui, Bei Wang, Shengli Yang, Hongwei Yu e Lidan Ye. "Enhancing Acetophenone Tolerance of Anti-Prelog Short-Chain Dehydrogenase/Reductase EbSDR8 Using a Whole-Cell Catalyst by Directed Evolution". Catalysts 12, n. 9 (19 settembre 2022): 1071. http://dx.doi.org/10.3390/catal12091071.
Testo completoAbstract (sommario):
The short-chain dehydrogenase/reductase (SDR) from Empedobacter brevis ZJUY-1401 (EbSDR8, GenBank: ALZ42979.1) is a promising biocatalyst for the reduction of acetophenone to (R)-1-phenylethanol, but its industrial application is restricted by its insufficient tolerance to acetophenone. In this paper, we developed a chromogenic reaction-based high-throughput screening method and employed directed evolution to enhance the acetophenone tolerance of EbSDR8. The resulting variant, M190V, showed 74.8% improvement over the wild-type in specific activity when catalyzing the reduction of 200 mM acetophenone. Kinetic analysis revealed a 70% enhancement in its catalytic efficiency (kcat/Km). Molecular docking was conducted to reveal the possible mechanism behind the improved acetophenone tolerance, and the result implied that the M190V mutation is conducive to the binding and release of coenzyme. Aside from the improved catalytic performance when dealing with a high concentration of acetophenone, other features of M190V, such as a broad pH range (6.0 to 10.5), low optimal cosubstrate concentration (1% isopropanol), and a temperature optimum close to that of E. coli cells (35 °C), also contribute to its practical application as a whole-cell catalyst. In this study, we first designed a directed evolution means to engineer the enzyme and obtained the positive variant which has a high activity under high concentrations of acetophenone. After that, we optimized the catalytic performance of the variant to adapt to industrial applications.
23
Manning, Jonathan R., Matthew A. Bailey, Dinesh C. Soares, Donald R. Dunbar e John J. Mullins. "In silico structure-function analysis of pathological variation in the HSD11B2 gene sequence". Physiological Genomics 42, n. 3 (agosto 2010): 319–30. http://dx.doi.org/10.1152/physiolgenomics.00053.2010.
Testo completoAbstract (sommario):
11β-Hydroxysteroid dehydrogenase type 2 (11βHSD2) is a short-chain dehydrogenase/reductase (SDR) responsible for inactivating cortisol and preventing its binding to the mineralocorticoid receptor (MR). Nonfunctional mutations in HSD11B2, the gene encoding 11βHSD2, cause the hypertensive syndrome of apparent mineralocorticoid excess (AME). Like other such Mendelian disorders, AME is rare but has nevertheless helped to illuminate principles fundamental to the regulation of blood pressure. Furthermore, polymorphisms in HSD11B2 have been associated with salt sensitivity, a major risk factor for cardiovascular mortality. It is therefore highly likely that sequence variation in HSD11B2, having subtle functional ramifications, will affect blood pressure in the wider population. In this study, a three-dimensional homology model of 11βHSD2 was created and used to hypothesize the functional consequences in terms of protein structure of published mutations in HSD11B2. This approach underscored the strong genotype-phenotype correlation of AME: severe forms of the disease, associated with little in vivo enzyme activity, arise from mutations occurring in invariant alignment positions. These were predicted to exert gross structural changes in the protein. In contrast, those mutations causing a mild clinical phenotype were in less conserved regions of the protein that were predicted to be relatively more tolerant to substitution. Finally, a number of pathogenic mutations are shown to be associated with regions predicted to participate in dimer formation, and in protein stabilization, which may therefore suggest molecular mechanisms of disease.
24
Yamaguchi, Hideaki, Yoshinori Kanayama, Junichi Soejima e Shohei Yamaki. "Changes in the Amounts of the NAD-dependent Sorbitol Dehydrogenase and Its Involvement in the Development of Apple Fruit". Journal of the American Society for Horticultural Science 121, n. 5 (settembre 1996): 848–52. http://dx.doi.org/10.21273/jashs.121.5.848.
Testo completoAbstract (sommario):
Seasonal changes in the amounts of the NAD-dependent sorbitol dehydrogenase (NAD-SDH) (enzyme code, 1.1.1.14) protein in developing apple (Malus pumila Mill var. domestica Schneid) fruit were determined by immunoblotting analysis. The amounts of the enzyme protein were very low in young fruit and rose as fruit matured. The weak correlation between enzyme protein and NAD-SDH activity and also the changes in NAD-SDH specific activity suggested that there could be posttranslational modification to the pre-existing enzyme or isoenzyme(s) of NAD-SDH. The changes in the amounts of NAD-SDH protein did not show the same pattern as those in relative growth rate, which is used to express sink activity, especially in young fruit. The role of NAD-SDH on sink activity in apple fruit, therefore, could not be explained simply by the amount and activity of the enzyme. In young fruit, it seems that enzymes other than NAD-SDH would be more directly related with fruit growth.
25
Bianco, Riccardo Lo, Mark Rieger e She-Jean S. Sung. "Sorbitol Metabolism in Growing Tissues of Peach". HortScience 32, n. 3 (giugno 1997): 530C—530. http://dx.doi.org/10.21273/hortsci.32.3.530c.
Testo completoAbstract (sommario):
Sorbitol is the major photosynthetic product in peach. In sink tissues, sorbitol is converted to fructose via the NAD-dependent enzyme sorbitol dehydrogenase (SDH). A new assay is described that allows rapid, simple quantitation of SDH activity in growing shoot tips, root tips, and fruits. The activity was measured on the crude extract desalted with a Saphadex G-25 column to eliminate small molecules such as sugars and nucleotides. Optimum buffer type and pH for the enzyme as well as degradation by proteolytic enzymes and stability over time were determined in the present study. Inhibition by dithiothreitol (DTT) was detected at an inhibitor concentration as low as 2 mM, proving the similarity with mammalian SDH. Storage of samples at 4°C overnight resulted in significant loss of enzyme activity. Using this assay, we also correlated SDH activity with sink strength in peach.
26
Satué, Katy, Laura Miguel-Pastor, Deborah Chicharro e Juan Carlos Gardón. "Hepatic Enzyme Profile in Horses". Animals 12, n. 7 (29 marzo 2022): 861. http://dx.doi.org/10.3390/ani12070861.
Testo completoAbstract (sommario):
For diagnostic purposes, liver enzymes are usually classified into hepatocellular and cholestatic. These two groups of equine liver-specific enzymes include sorbitol dehydrogenase (SDH), glutamate dehydrogenase (GLDH), γ-glutamyl transferase (GGT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), and alkaline phosphatase (ALP). SDH and GLDH mostly reflect hepatocellular injury and cholestasis, while GGT expresses high values in biliary necrosis or hyperplasia. Likewise, AST, LDH, and ALP also reflect hepatocellular and biliary disease, but these enzymes are not liver specific. From the clinical point of view of the course of liver or biliary disease, AST and ALP are indicative of chronic disease, whereas SDH, GGT, and GLDH indicate an acute course. The patterns of enzymatic changes at the blood level are associated with different types of liver pathologies (infectious, inflammatory, metabolic, toxic, etc.). Increases in hepatocellular versus biliary enzyme activities are indicative of a particular process. There are different ways to diagnose alterations at the hepatic level. These include the evaluation of abnormalities in the predominant pattern of hepatocellular versus cholestatic enzyme abnormalities, the mild, moderate, or marked (5–10-fold or >10-fold) increase in enzyme abnormality concerning the upper limit of the reference range, the evolution over time (increase or decrease) and the course of the abnormality (acute or chronic).
27
Dreval, A. V., L. A. Marchenkova, O. P. Kuznetsova, G. A. Onoprienko, V. I. Shumsky, I. A. Komissarova, Y. R. Narcissov et al. "Diagnostic value of redox leukocyte enzymes in postmenopausal osteopenia". Problems of Endocrinology 45, n. 2 (3 aprile 1999): 31–35. http://dx.doi.org/10.14341/probl11745.
Testo completoAbstract (sommario):
Activities of redox enzymes of peripheral blood leukocytes is studied in patients with postmenopausal osteopenia. Neutrophil myeloperoxidase (MP), alkaline phosphatase (AP) and lymphocyte succinate dehydrogenase (SDH), and succinate.cytochrome C oxyreductase (SCOR) activities were measured by the cytochemical method. Densitometric examinations of 49 postmenopausal women without risk of secondary osteoporosis revealed osteoporosis in 15 (31%)) and osteopenia in 24 (49%)); in 10 (20%o) mineral compactness of bones was normal. AP and SDH activities were increased and SCOR and MP activities normal in patients with osteopenia. Changes in the activities of AL and SDH in subjects with different duration of the postmenopausal period indicate that the main factor affecting the activities of these enzymes was osteopenia but not the duration of postmenopause or age. Significant correlations between enzyme values and mineral compactness of the spine were the most numerous during the first three years of postmenopause, and therefore changes in leukocyte enzyme activities are apparently not caused by inflammations associated with chronic macroand microfractures of the vertebrae but by osteopenia. The detected specific correlation between enzyme activities and localization of the pathological process in certain segments of the skeleton permits us to propose that leukocyte AL and SDH values may serve as criteria for optimal choice of skeletal area for subsequent densitometry or x-ray examination.
28
Marlow, Gary C., e Wayne H. Loescher. "Sorbitol Metabolism, the Climacteric, and Watercore in Apples". Journal of the American Society for Horticultural Science 110, n. 5 (settembre 1985): 676–80. http://dx.doi.org/10.21273/jashs.110.5.676.
Testo completoAbstract (sommario):
Abstract Extraction and assay of sorbitol dehydrogenase (SDH) throughout fruit maturation of 3 apple (Malus domestica Borkh.) cultivars, watercore-resistant ‘Golden Delicious,’ occasionally susceptible ‘McIntosh’, and normally susceptible ‘Starkrimson,’ showed no relationship between susceptibility to watercore and extractable enzyme activity. There was, however, a relationship between increased SDH activity and onset of the climacteric as measured by ethylene and CO2 evolution, suggesting that SDH, like certain other enzymes, increases during maturation.
29
ZHU, Xiaohong, Guiliang TANG e Gad GALILI. "The catabolic function of the α-aminoadipic acid pathway in plants is associated with unidirectional activity of lysine–oxoglutarate reductase, but not saccharopine dehydrogenase". Biochemical Journal 351, n. 1 (26 settembre 2000): 215–20. http://dx.doi.org/10.1042/bj3510215.
Testo completoAbstract (sommario):
Whereas plants and animals use the α-aminoadipic acid pathway to catabolize lysine, yeast and fungi use the very same pathway to synthesize lysine. These two groups of organisms also possess structurally distinct forms of two enzymes in this pathway, namely lysine–oxoglutarate reductase (lysine–ketoglutarate reductase; LKR) and saccharopine dehydrogenase (SDH): in plants and animals these enzymes are linked on to a single bifunctional polypeptide, while in yeast and fungi they exist as separate entities. In addition, yeast LKR and SDH possess bi-directional activities, and their anabolic function is regulated by complex transcriptional and post-transcriptional controls, which apparently ascertain differential accumulation of intermediate metabolites; in plants, the regulation of the catabolic function of these two enzymes is not known. To elucidate the regulation of the catabolic function of plant bifunctional LKR/SDH enzymes, we have used yeast as an expression system to test whether a plant LKR/SDH also possesses bi-directional LKR and SDH activities, similar to the yeast enzymes. The Arabidopsis enzyme complemented a yeast SDH, but not LKR, null mutant. Identical results were obtained when deletion mutants encoding only the LKR or SDH domains of this bifunctional polypeptide were expressed individually in the yeast cells. Moreover, activity assays showed that the Arabidopsis LKR possessed catabolic, but not anabolic, activity, and its uni-directional activity stems from its structure rather than its linkage to SDH. Our results suggest that the uni-directional activity of LKR plays an important role in regulating the catabolic function of the α-amino adipic acid pathway in plants.
30
Noone, A., Y. Lao, T. Crawford, D. Kennedy, J. Martin, A. Ferrante, D. Wabnitz e A. Kontos. "O035 Elevated liver enzymes in paediatric sleep disordered breathing". SLEEP Advances 3, Supplement_1 (1 ottobre 2022): A14. http://dx.doi.org/10.1093/sleepadvances/zpac029.034.
Testo completoAbstract (sommario):
Abstract Introduction Paediatric sleep disordered breathing (SDB) is associated with adverse cardiovascular outcomes. Non-alcoholic fatty liver disease (NAFLD) and dyslipidaemia are potential modifiable risk factors for cardiovascular disease, often coexisting in adults with SDB. Increases in lipid outputs from the liver have been identified in obese adults and children with SDB. Whether children with SDB compared to healthy non-snoring controls have evidence of elevated serum lipids and associated liver enzyme changes were assessed. Methods Seventy-five children (SDB=49, controls=26) between the ages of 6-17 years matched for age, gender and BMI underwent overnight polysomnography to measure SDB severity and provided a fasting blood sample to assess lipid and liver panels. Results OAHI was significantly increased in children with SDB compared to healthy non-snoring controls (p < 0.05). Serum potassium, alanine aminotransferase and lactate dehydrogenase were significantly increased in children with SDB, while albumin was significantly decreased (p < 0.05). No differences were found between serum lipid levels. Conclusion The presence of paediatric SDB may increase the risk of developing NAFLD. Further investigation is required to determine whether routine assessment of liver enzymes should be implemented in paediatric SDB. Whether surgical removal of the adenoids and tonsils to treat paediatric SDB can stabilise liver enzyme levels requires further research.
31
Muhammad Rafiq Khan, M Khan e A Shah. "A Study of Heart Enzyme Profile in Myocardial Infarction". Scientific Inquiry and Review 2, n. 2 (30 aprile 2018): 01–10. http://dx.doi.org/10.32350/sir/22/020201.
Testo completoAbstract (sommario):
The work reported in this article was carried out to determine the role of cardiac enzymes in myocardial infarction. The cardiac enzyme levels of 30 normal subjects and 30 infarcted subjects were determined and compared by statistical analysis. The peak values of the statistical averages of CPK, AST and LDH were compared. The comparison indicated that the peak levels of cardiac enzymes in infarcted subjects were 1.5 to 6.1 times that of the normal subjects. The results also showed that the correlation between the cardiac enzyme concentration levels and the gravity of myocardial infarction was highly significant. From the results, it may be concluded that whenever there is an occurrence of myocardial infarction, higher levels of cardiac enzymes will be present in the blood of the infracted subjects as compared to that in the blood of normal subjects.
32
Pisoschi, Catalina, Virgil Darie e Mihai Serban. "STUDY OF RENAL SORBITOLDEHYDROGENASE IN EXPERIMENTAL DIABETIC NEPHROPATHY". SOUTHERN BRAZILIAN JOURNAL OF CHEMISTRY 6, n. 7 (20 dicembre 1998): 77–82. http://dx.doi.org/10.48141/sbjchem.v6.n7.1998.76_1998_2.pdf.
Testo completoAbstract (sommario):
The link between the polyol pathway and the ocular complications of diabetes mellitus is explained by the excessive storage of sorbitol and the release of osmotic stress. The renal complications could also be explained by the osmotic hypothesis, but the polyol pathway activity is reduced in this case. The study of sorbitol dehydrogenase (SDH) activity, one of the enzymes involved in the catabolism of glucose by this pathway in renal and hepatic homogenates from diabetic animals, shows a constant increase of the hepatic enzyme activity compared to that at the renal level. The different variations of the renal SDH activity can be explained by the effect of hyperglycemia on the active form of the enzyme and its inactivation by nonenzymatic glycosylation.
33
Zhu, Xiaohong, Guiliang Tang e Gad Galili. "The Activity of theArabidopsisBifunctional Lysine-ketoglutarate Reductase/Saccharopine Dehydrogenase Enzyme of Lysine Catabolism Is Regulated by Functional Interaction between Its Two Enzyme Domains". Journal of Biological Chemistry 277, n. 51 (21 ottobre 2002): 49655–61. http://dx.doi.org/10.1074/jbc.m205466200.
Testo completoAbstract (sommario):
Lysine-ketoglutarate reductase/saccharopine dehydrogenase (LKR/SDH) is a bifunctional enzyme catalyzing the first two steps of lysine catabolism in animals and plants. To elucidate the biochemical signification of the linkage between the two enzymes of LKR/SDH, namely lysine ketoglutarate and saccharopine dehydrogenase, we employed various truncated and mutatedArabidopsisLKR/SDH polypeptides expressed in yeast. Activity analyses of the different recombinant polypeptides under conditions of varying NaCl levels implied that LKR, but not SDH activity, is regulated by functional interaction between the LKR and SDH domains, which is mediated by the structural conformation of the linker region connecting them. Because LKR activity of plant LKR/SDH enzymes is also regulated by casein kinase 2 phosphorylation, we searched for such potential regulatory phosphorylation sites using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and site-directed mutagenesis. This analysis identified Ser-458 as a candidate for this function. We also tested a hypothesis suggesting that an EF-hand-like sequence at the C-terminal part of the LKR domain functions in a calcium-dependent assembly of LKR/SDH into a homodimer. We found that this region is essential for LKR activity but that it does not control a calcium-dependent assembly of LKR/SDH. The relevance of our results to thein vivofunction of LKR/SDH in lysine catabolism in plants is discussed. In addition, because the linker region between LKR and SDH exists only in plants but not in animal LKR/SDH enzymes, our results suggest that the regulatory properties of LKR/SDH and, hence, the regulation of lysine catabolism are different between plants and animals.
34
Hederstedt, L., e L. O. Hedén. "New properties of Bacillus subtilis succinate dehydrogenase altered at the active site. The apparent active site thiol of succinate oxidoreductases is dispensable for succinate oxidation". Biochemical Journal 260, n. 2 (1 giugno 1989): 491–97. http://dx.doi.org/10.1042/bj2600491.
Testo completoAbstract (sommario):
Mammalian and Escherichia coli succinate dehydrogenase (SDH) and E. coli fumarate reductase apparently contain an essential cysteine residue at the active site, as shown by substrate-protectable inactivation with thiol-specific reagents. Bacillus subtilis SDH was found to be resistant to this type of reagent and contains an alanine residue at the amino acid position equivalent to the only invariant cysteine in the flavoprotein subunit of E. coli succinate oxidoreductases. Substitution of this alanine, at position 252 in the flavoprotein subunit of B. subtilis SDH, by cysteine resulted in an enzyme sensitive to thiol-specific reagents and protectable by substrate. Other biochemical properties of the redesigned SDH were similar to those of the wild-type enzyme. It is concluded that the invariant cysteine in the flavoprotein of E. coli succinate oxidoreductases corresponds to the active site thiol. However, this cysteine is most likely not essential for succinate oxidation and seemingly lacks an assignable specific function. An invariant arginine in juxtaposition to Ala-252 in the flavoprotein of B. subtilis SDH, and to the invariant cysteine in the E. coli homologous enzymes, is probably essential for substrate binding.
35
DAI, Z., Y. YIN e Z. WANG. "Activities of key enzymes involved in starch synthesis in grains of wheat under different irrigation patterns". Journal of Agricultural Science 147, n. 4 (22 aprile 2009): 437–44. http://dx.doi.org/10.1017/s0021859609008612.
Testo completoAbstract (sommario):
SUMMARYIt is generally accepted that sucrose phosphate synthase (SPS), sucrose synthase (SuSy), ADP-glucose pyrophosphorylase (AGPase), soluble starch synthase (SSS), granule-bound starch synthase (GBSS) and starch branching enzyme (SBE) play a key role in starch synthesis in wheat grains. Starch synthesis in wheat grains is influenced by genotype and environment. However, what is not known is the degree of variation in enzyme activities during starch accumulation of wheat cultivars field-grown in different water regimes. The present study was undertaken to determine whether irrigation patterns could cause differences in starch accumulation and activities of key enzymes involved in starch synthesis. Starch accumulation and related enzyme activities were investigated in two winter wheat varieties, JM20 and BY535, differing in grain starch content, under two irrigation patterns. Results showed that soil water deficit led to an increase at early grain filling and decrease during late grain filling in starch accumulation rate (SAR) and activities of key enzymes involved in starch synthesis, especially AGPase, SSS and SBE. Water deficit enhanced grain starch accumulation in two wheat cultivars, suggesting that rainfed treatments increase physiological activities during early grain filling and promote starch accumulation. Furthermore, the change of SAR is consistent with SuSy, AGPase, SSS and GBSS. The results suggest that these enzymes play a key role in starch synthesis, and the decrease of photosynthate produced in the source organ is not the factor inhibiting starch accumulation.
36
Kuppusamy, Chinnadurai, Arul Ganesh, Karthikeyeni Sambanthan, Eyini Muthukumarasamy e Balaji Paulraj*. "Enzyme modulation studies of Fumaronitrile on fresh water fish Oreochromis mossambicus". International Journal of Bioassays 5, n. 11 (31 ottobre 2016): 5050. http://dx.doi.org/10.21746/ijbio.2016.11.0011.
Testo completoAbstract (sommario):
The present study was directed to analyse the potential enzymatic variation efficiency of fumaronitrile on fresh water fish tilapia (Oreochromis mossambicus). To study the acute toxicity of xenobiotic five different concentrations (20, 40, 60, 80 and 100ppb) of fumaronitrile along with control group was maintained for over 96 hrs. At every 1 hr. fishes was monitor both control and treatment groups. The LC50 value was found to be as 60ppb. To study the chronic toxicity of xenobiotic three different concentrations (2ppb, 4ppb and 6ppb) of fumaronitrile along with control group was maintained for over 100 days. At 60, 80,100 days fishes was sacrificed both control and treatment groups and the organs such as liver were collected to analyse the changes in testicular enzyme activities and an increasing pattern for both antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD) was observed. Enzyme assay is one of the important methods to evaluate the toxicity of xenobiotic. At present, no report is available on the effect of fumaronitrile on antioxidant enzymes and testicular enzyme activities. This study focus light on the effects of fumaronitrile in antioxidant enzymes CAT, SOD and testicular enzymes ALP, ACP, LDH and SDH in Oreochromis mossambicus.
37
Oppermann, Udo C. T., Charlotta Filling e Hans Jörnvall. "Forms and functions of human SDR enzymes". Chemico-Biological Interactions 130-132 (gennaio 2001): 699–705. http://dx.doi.org/10.1016/s0009-2797(00)00301-x.
Testo completo
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Kim, Geun-Joong, Dong-Eun Lee e Hak-Sung Kim. "Construction and Evaluation of a Novel Bifunctional N-Carbamylase–d-Hydantoinase Fusion Enzyme". Applied and Environmental Microbiology 66, n. 5 (1 maggio 2000): 2133–38. http://dx.doi.org/10.1128/aem.66.5.2133-2138.2000.
Testo completoAbstract (sommario):
ABSTRACT A fully enzymatic process employing two sequential enzymes,d-hydantoinase and N-carbamylase, is a typical case requiring combined enzyme activity for the production ofd-amino acids. To test the possibility of generating a bifunctional fusion enzyme, we constructed a fusion protein via end-to-end fusion of a whole gene that encodes an intact protein at the N terminus of the d-hydantoinase. Firstly, maltose-binding protein (MBP) gene of E. coli was fused withd-hydantoinase gene from Bacillus stearothermophilus SD1, and the properties of the resulting fusion protein (MBP-HYD) were compared with those of natived-hydantoinase. Gel filtration and kinetic analyses clearly demonstrated that the typical characteristics ofd-hydantoinase are maintained even in a fusion state. Based on this result, we constructed an artificial fusion enzyme composed of the whole length of N-carbamylase (304 amino acids [aa]) from Agrobacterim radiobacter NRRL B11291 andd-hydantoinase (471 aa). The fusion enzyme (CAB-HYD) was functionally expressed with an expected molecular mass of 86 kDa and efficiently converted exogenous hydantoin derivatives to thed-amino acids. A related d-hydantoinase (HYD1) gene from Bacillus thermocatenulatus GH2 was also fused with the N-carbamylase gene at its N terminus. The resulting enzyme (CAB-HYD1) was bifunctional as expected and showed better performance than the CAB-HYD fusion enzyme. The conversion of hydantoin derivatives to corresponding amino acids by the fusion enzymes was much higher than that by the separately expressed enzymes, and comparable to that by the coexpressed enzymes. Thus, the fusion enzyme might be useful as a potential biocatalyst for the production of nonnatural amino acids.
39
Frye, Stephen V. "Inhibitors of Sa-Reductase". Current Pharmaceutical Design 2, n. 1 (febbraio 1996): 59–84. http://dx.doi.org/10.2174/1381612802666220920215559.
Testo completoAbstract (sommario):
Abstract: The enzyme steroid Sa-reductase (SAR) catalyzes the c nversion of Ll4 steroids to the corresponding saturated steroids and plays a significant role in developmental biology. Dihydrotestosterone, a product of Sa-reduction of testosterone, has been implicated in the pathology of benign prostatic hyperplasia, acne and male pattern baldness. Two isozymes of SAR are now known and the relative roles of these enzymes in developmental physiology and in the pathophysiology of androgen related disorders is the subject of much current research. Progress in the development of potent isozyme selective and dual inhibitors of SAR is reviewed with an emphasis on structure activity relationships as well as efficacy in animal models of benign prostatic hyperplasia and human clinical studies.
40
Dunn, S. E., e R. N. Michel. "Coordinated expression of myosin heavy chain isoforms and metabolic enzymes within overloaded rat muscle fibers". American Journal of Physiology-Cell Physiology 273, n. 2 (1 agosto 1997): C371—C383. http://dx.doi.org/10.1152/ajpcell.1997.273.2.c371.
Testo completoAbstract (sommario):
We studied the coordinated regulation of myosin heavy chains (MHC) and metabolic enzymes within individual overloaded adult rat plantaris fibers. This was done using monoclonal antibodies raised against distinct developmental and adult MHCs, and quantitative microphotometric succinate dehydrogenase (SDH) and glycerol-3-phosphate dehydrogenase (GPDH) enzyme assays. Overload shifted MHC expression in the order IIb-->IIx-->IIa-->alpha/I, with a tripling of cells coexpressing I and alpha-MHC, and a transient reexpression of two embryonic MHC and the neonatal isoform in preexisting myofibers. Overload caused a rapid, size-independent, 50% decrease in GPDH activity across all cell types, which recovered by 6 wk. Fiber SDH activities varied according to MHC composition, such that overloaded fibers coexpressing IIa MHC displayed control slow fiber SDH levels, whereas cells expressing IIx and IIb MHC displayed a transient 30% increase in SDH that recovered by 6 wk. Our results suggest that during overload, fibers adapt progressively to the new functional requirements and display more efficient cellular energy utilization and delivery characteristics. The time course of adaptations suggests a role for glycolytic enzymes in the initiation of these transformations.
41
Bianco, Riccardo Lo, Mark Rieger e She-Jean S. Sung. "Activities of Sucrose and Sorbitol Metabolizing Enzymes in Vegetative Sinks of Peach and Correlation with Sink Growth Rate". Journal of the American Society for Horticultural Science 124, n. 4 (luglio 1999): 381–88. http://dx.doi.org/10.21273/jashs.124.4.381.
Testo completoAbstract (sommario):
Terminal portions of `Flordaguard' peach roots [Prunus persica (L.) Batsch] were divided into six segments and the activities of NAD+-dependent sorbitol dehydrogenase (SDH), sorbitol oxidase (SOX), sucrose synthase (SS), soluble acid invertase (AI), and soluble neutral invertase (NI) were measured in each segment 10, 15, and 20 days after seed germination. The same type of experiment was conducted with terminal portions of `Flordaguard' and `Nemaguard' peach shoots except that one of the six segments consisted of the leaflets surrounding the apex. Independent of the age of individual roots, activities of SDH and AI were consistently highest in the meristematic portion and decreased with tissue maturation. In shoots, AI was the most active enzyme in the elongating portion subtending the apex, whereas SDH was primarily associated with meristematic tissues. A positive correlation between SDH and AI activities was found in various developmental zones of roots (r = 0.96) and shoots (r = 0.90). Sorbitol and sucrose contents were low in roots regardless of distance from tip, while sucrose showed a decreasing trend with distance and sorbitol, fructose, and glucose increased with distance from the meristem in shoots. Activity of SDH in internodes, but not apices, correlated with shoot elongation rate of both cultivars, whereas activities of other enzymes did not correlate with shoot elongation rate. We conclude that AI and SDH are the predominant enzymes of carbohydrate catabolism and the best indicators of sink growth and development in vegetative sinks of peach.
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HOSHI, Ayumu, Motoko TAKAHASHI, Junichi FUJII, Theingi MYINT, Hideaki KANETO, Keiichiro SUZUKI, Yoshimitsu YAMASAKI, Takenobu KAMADA e Naoyuki TANIGUCHI. "Glycation and inactivation of sorbitol dehydrogenase in normal and diabetic rats". Biochemical Journal 318, n. 1 (15 agosto 1996): 119–23. http://dx.doi.org/10.1042/bj3180119.
Testo completoAbstract (sommario):
Sorbitol dehydrogenase (SDH) is involved in the polyol pathway, which plays an important role in the pathogenesis of diabetic complications. We have measured the tissue distributions of SDH mRNA, both the immunoreactive enzyme levels and the enzyme activity. SDH mRNA was especially abundant in liver, kidney and testis. Both the activity and enzyme content are high in liver and kidney but not in testis. The discrepancy between mRNA and immunoreactive enzyme levels and the activity of SDH observed in testis was also seen in livers of streptozotocin-induced diabetic rats. SDH was found to exist in both glycated and non-glycated forms, with larger amounts of the glycated protein in the diabetic liver. Moreover, after incubation of purified enzyme with glucose or fructose, its activity was markedly decreased. These results indicate that glycation causes a decrease in SDH activity in liver under diabetic conditions. The same post-transcriptional event might occur to decrease the activity of SDH in testis in normal animals.
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Bianco, Riccardo Lo, Mark Rieger e Shi-Jean S. Sung. "Carbohydrate Metabolism of Vegetative and Reproductive Sinks in the Late-maturing Cultivar Encore". HortScience 33, n. 3 (giugno 1998): 541c—541. http://dx.doi.org/10.21273/hortsci.33.3.541c.
Testo completoAbstract (sommario):
Activities of major sorbitol and sucrose metabolizing enzymes and carbohydrate contents were followed during the growth season of `Encore' peach fruits and developing shoot tips. In fruit flesh, sucrose synthase (SS) was present during stage I of growth, when cells are actively dividing, and NAD+-dependent sorbitol dehydrogenase (SDH) during stage III, when cells enlarge actively. Acid invertase (AI) revealed the best correlation with relative growth rate (RGR) of fruits during the entire season. Activities of all carbohydrate metabolizing enzymes were not detectable in fruit flesh during seed filling and pit hardening, when RGR of fruits was the slowest. The highest content of sucrose was in concert with low levels of sucrose metabolizing enzyme activities toward the end of fruit development. In shoot tips, SDH had low activity at the beginning and end of the season when vegetative growth was slowest and a 2:1 sorbitol: sucrose ratio was present. Mid-growing season was, on the other hand, characterized by an increase in SDH activity and a 1:1 sorbitol: sucrose ratio. In `Nemaguard' seedlings, only SDH activity showed a positive correlation with shoot growth. Also, in root tips of `Nemaguard' seedlings SDH exhibited its highest activity, even higher than AI activity in the same roots. We concluded that in peach sucrose may represent the major carbon form used for fruit growth, while sorbitol seems to play a predominant role in vegetative growth.
44
Zhao, Zhongwei, Richard A. Rothery e Joel H. Weiner. "Effects of site-directed mutations in Escherichia coli succinate dehydrogenase on the enzyme activity and production of superoxide radicalsThis paper is one of a selection of papers published in this Special Issue, entitled CSBMCB — Membrane Proteins in Health and Disease." Biochemistry and Cell Biology 84, n. 6 (dicembre 2006): 1013–21. http://dx.doi.org/10.1139/o06-188.
Testo completoAbstract (sommario):
Escherichia coli succinate dehydrogenase (SdhCDAB) catalyzes the oxidation of succinate to fumarate in the Krebs cycle, and during turnover, it produces superoxide radicals. SdhCDAB is a good model system for the succinate dehydrogenase (Sdh) found in the mitochondrial respiratory chain (complex II), as the subunits are structural homologues. Although mutations in sdh genes are reportedly associated with a variety of mitochondria-related diseases, the molecular mechanism of these diseases is poorly understood. We have investigated the effects of site-directed mutations around the heme (SdhD-H71L and SdhC-H91L), and at the ubiquinone-binding site (Q site; SdhC-I28E), on enzyme activity and production of superoxide radicals. The mutations SdhD-H71L and SdhC-I28E, but not SdhC-H91L, significantly reduce the succinate–ubiquinone reductase activity of the enzyme. All 3 mutant enzymes produce more superoxide than the wild-type enzyme, indicating that disturbance of the heme or the Q site can enhance superoxide production. The presence of a Q-site inhibitor reduces superoxide production significantly. Furthermore, the yield of superoxide is substrate dependent and increases with succinate concentration from 0.1 to 10 mmol/L. Our results indicate that, in SdhCDAB, the Q site with bound ubiquinone is an important source of superoxide radicals.
45
Davis, David A., Kathleen E. Singer, Maria De La Luz Sierra, Masashi Narazaki, Fuquan Yang, Henry M. Fales, Robert Yarchoan e Giovanna Tosato. "Identification of carboxypeptidase N as an enzyme responsible for C-terminal cleavage of stromal cell-derived factor-1α in the circulation". Blood 105, n. 12 (15 giugno 2005): 4561–68. http://dx.doi.org/10.1182/blood-2004-12-4618.
Testo completoAbstract (sommario):
Abstract The chemokine stromal-derived factor-1α (SDF-1α) is an essential regulator of hematopoiesis, lymphocyte homing, pre-B-cell growth, and angiogenesis. As SDF-1α is constitutively expressed in many tissues, chemokine function is mostly regulated by proteolytic degradation. Human serum cleaves the 68-amino acid chemokine, SDF-1α, at both termini. The enzyme or enzymes responsible for the removal of the carboxy-terminal lysine from SDF-1α, leading to significant reduction in biologic activity, have not been identified. Using a new biochemical assay for measuring the carboxy-terminal cleavage activity, we purified from serum and plasma a peptidase that specifically removes the carboxy-terminal lysine from SDF-1α and identified it as carboxypeptidase N (CPN, also known as kininase I, arginine carboxypeptidase, and anaphylotoxin inactivator). We demonstrate that SDF-1α in serum and plasma lacks the carboxy terminal lysine, and depletion of CPN from serum and plasma significantly reduces the SDF-1α carboxypeptidase activity. Purified CPN effectively and specifically removes the carboxy-terminal lysine from SDF-1α and significantly reduces the chemokine's biologic activity as a pre-B-cell growth factor and chemoattractant. Thus, in addition to its role as a regulator of the biologic activity of kinins and anaphylatoxins, CPN is an important regulator of the biologic activity of SDF-1α by reducing the chemokine-specific activity. (Blood. 2005;105:4561-4568)
46
Höppner, Astrid, Dietmar Schomburg e Karsten Niefind. "Enzyme-substrate complexes of the quinate/shikimate dehydrogenase from Corynebacterium glutamicum enable new insights in substrate and cofactor binding, specificity, and discrimination". Biological Chemistry 394, n. 11 (1 novembre 2013): 1505–16. http://dx.doi.org/10.1515/hsz-2013-0170.
Testo completoAbstract (sommario):
Abstract Quinate dehydrogenase (QDH) catalyzes the reversible oxidation of quinate to 3-dehydroquinate by nicotineamide adenine dinucleotide (NADH) and is involved in the catabolic quinate metabolism required for the degradation of lignin. The enzyme is a member of the family of shikimate/quinate dehydrogenases (SDH/QDH) occurring in bacteria and plants. We characterized the dual-substrate quinate/shikimate dehydrogenase (QSDH) from Corynebacterium glutamicum (CglQSDH) kinetically and revealed a clear substrate preference of CglQSDH for quinate compared with shikimate both at the pH optimum and in a physiological pH range, which is a remarkable contrast to closely related SDH/QDH enzymes. With respect to the cosubstrate, CglQSDH is strictly NAD(H) dependent. These substrate and cosubstrate profiles correlate well with the details of three atomic resolution crystal structures of CglQSDH in different functional states we report here: with bound NAD+ (binary complex) and as ternary complexes with NADH plus either shikimate or quinate. The CglQSDH-NADH-quinate structure is the first complex structure of any member of the SDH/QDH family with quinate. Based on this novel structural information and systematic sequence and structure comparisons with closely related enzymes, we can explain the strict NAD(H) dependency of CglQSDH as well as its discrimination between shikimate and quinate.
47
Vladutiu, Georgirene D., e Reid R. Heffner. "Succinate Dehydrogenase Deficiency". Archives of Pathology & Laboratory Medicine 124, n. 12 (1 dicembre 2000): 1755–58. http://dx.doi.org/10.5858/2000-124-1755-sdd.
Testo completoAbstract (sommario):
Abstract Background.—Partial succinate dehydrogenase deficiency (15% to 50% of normal reference enzyme activity) in skeletal muscle causes mitochondrial myopathy with various symptoms, for example, brain involvement, cardiomyopathy, and/or exercise intolerance. The deficiency may be isolated or may coexist with other respiratory-chain enzyme defects. The histopathologic assessment of succinate dehydrogenase activity in muscle biopsies of patients with suspected mitochondrial myopathies has focused on the finding of increased staining, usually in ragged-red fibers, rather than on reduced staining. Objectives.—To determine the prevalence of muscle succinate dehydrogenase deficiency among patients with respiratory-chain defects and to determine whether the reduced activity is present histochemically and is comparable to the quantitative reduction found in muscle homogenates. Patients and Methods.—One hundred eight muscle biopsies were evaluated from patients with suspected mitochondrial myopathies by qualitative histochemical analysis and quantitative biochemical analyses of respiratory-chain enzymes using standard methodologies. Results.—Fifty-two patients had defects in respiratory-chain complexes; of these patients, 12 (23%) had partial deficiencies in succinate dehydrogenase activity either alone or together with reductions in other enzymes. The reduced activity was detectable histochemically in muscle biopsies with residual enzyme activity of up to 34% of the normal reference activity, while 2 biopsies with higher residual activity (49% and 68% of normal) could not be distinguished from normal biopsies. Conclusions—Of the patients with respiratory-chain enzyme defects, 23% had partial deficiencies of succinate dehydrogenase activity in muscle biopsies. This reduction could be detected histochemically in biopsies in most cases. The marked prevalence of succinate dehydrogenase deficiency among patients with respiratory-chain defects and its detection initially by histochemical analysis are important findings.
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Karboski, James A., Paul J. Godley, Paul A. Frohna, Michael W. Horton e William J. Reitmeyer. "Marked Digoxin-Likeimmunoreactive Factor Interference with an Enzyme Immunoassay". Drug Intelligence & Clinical Pharmacy 22, n. 9 (settembre 1988): 703–5. http://dx.doi.org/10.1177/106002808802200913.
Testo completoAbstract (sommario):
A case in which digoxin-like immunoreactive factors (DLIF) interfered with an enzyme immunoassay in a patient with renal insufficiency is reported. A 79-year-old woman was found to have a serum digoxin concentration (SDC) determined by enzyme immunoassay of 5.0 ng/ml. Although all subsequent SDC determined by the enzyme immunoassay system were elevated, identical samples run on a fluorescence polarization immunoassay revealed SDC within the therapeutic range. Marked DLIF-related assay interference has been reported to occur with some digoxin assays; however, the enzyme immunoassay methods have never been reported to cross-react to the magnitude seen in this case.
49
Dube, Praveen, A. Shwetha e B. B. Hosetti. "Impact of copper cyanide on the key metabolic enzymes of freshwater fish Catla catla (Hamilton)". Biotehnologija u stocarstvu 30, n. 3 (2014): 499–508. http://dx.doi.org/10.2298/bah1403499d.
Testo completoAbstract (sommario):
Short term toxicity experiments were conducted to study the effect of metal cyanide complex (copper cyanide) on the key metabolic enzymes viz., lactate dehydrogenase (LDH), succinate dehydrogenase (SDH), glucose-6 phosphate dehydrogenase (G6PDH), aspartate amino transferase (AST) alanine amino transferase (ALT), acid phosphatase (AcP) and alkaline phosphatase (ALP) activity in Catla catla juveniles. A total of 60 fingerlings were (2?0.5 cm; 1.5?0.2 g) exposed to two sublethal concentrations (0.253 and 0.152 mg/L) for a period of 15 days. Copper cyanide had significant (P> 0.05) effect on the key metabolic enzymes, the highest activities were observed in the group exposed to 0.253 mg/L. Results suggest that metal cyanide complex significantly altered enzyme activities of fish in both the sublethal concentrations.
50
Lomax, R. B., e W. R. Robertson. "The effects of hypo- and hyperthyroidism on fibre composition and mitochondrial enzyme activities in rat skeletal muscle". Journal of Endocrinology 133, n. 3 (giugno 1992): 375—NP. http://dx.doi.org/10.1677/joe.0.1330375.
Testo completoAbstract (sommario):
ABSTRACT Hypo- and hyperthyroidism have been associated with changes in the activities of mitochondrial enzymes in homogenates of skeletal muscles, but it is unclear whether such changes were due to changes in single fibre enzyme activities or to previously documented changes in relative numbers of fibres. In this study the activities of the mitochondrial enzymes α-glycerol phosphate dehydrogenase (m-αGPDH) and succinate dehydrogenase (SDH) were measured in single fibres of the soleus and gastrocnemius muscles of the rat by cytochemical assays. In the soleus muscles of hypothyroid animals there was a decrease in the mean percentage (± s.d.) of type II fibres from 8·0 ± 6·0 to 0·8 ± 1·9% (P < 0·05) and decreases in SDH activities in all fibre types (P < 0·005). In the gastrocnemius muscles of these animals there were no changes in fibre composition but type IIB fibres had reduced (P < 0·05) m-αGPDH activities. In the hyperthyroid animals, in which body weight had increased relative to the euthyroid animals, there were increases in the percentages of type IC and type II fibres in the soleus from 4·3 ± 1·7 to 13·1 – 9·0% (P < 0·05) and from 9·6 ± 7·2 to 33·4 ± 9·6% (P < 0·005) respectively and an increase in the percentage of type IIA fibres in the gastrocnemius from 92·9 ± 2·3 to 97·0 ± 2·9% (P < 0·05). However, there were no increases in single fibre mitochondrial enzyme activities. It is therefore suggested that the administration of moderate, growth-promoting doses of thyroid hormones to euthyroid animals can cause changes in muscle fibre composition without stimulating the activities of mitochondrial enzymes. Journal of Endocrinology (1992) 133, 375–380