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1
hÓgáin, Fionnán Ó. "Bíodh TnaG Againn!" Comhar 51, no. 5 (1992): 220. http://dx.doi.org/10.2307/25571800.
2
Feinneadha, Ciarán Ó. "TnaG - an ród a bhí romhainn." Comhar 54, no. 5 (1995): 10. http://dx.doi.org/10.2307/25572644.
3
Konan, Kouacou Vincent, and Charles Yanofsky. "Role of Ribosome Release in Regulation oftna Operon Expression in Escherichia coli." Journal of Bacteriology 181, no. 5 (March 1, 1999): 1530–36. http://dx.doi.org/10.1128/jb.181.5.1530-1536.1999.
Анотація:
ABSTRACT Expression of the degradative tryptophanase (tna) operon of Escherichia coli is regulated by catabolite repression and tryptophan-induced transcription antitermination. In cultures growing in the absence of added tryptophan, transcription of the structural genes of the tna operon is limited by Rho-dependent transcription termination in the leader region of the operon. Tryptophan induction prevents this Rho-dependent termination, and requires in-frame translation of a 24-residue leader peptide coding region, tnaC, that contains a single, crucial, Trp codon. Studies with a lacZ reporter construct lacking the spacer region between tnaC and the first major structural gene,tnaA, suggested that tryptophan induction might involvecis action by the TnaC leader peptide on the ribosome translating the tnaC coding region. The leader peptide was hypothesized to inhibit ribosome release at thetnaC stop codon, thereby blocking Rho’s access to the transcript. Regulatory studies with deletion constructs of thetna operon of Proteus vulgaris supported this interpretation. In the present study the putative role of thetnaC stop codon in tna operon regulation inE. coli was examined further by replacing the naturaltnaC stop codon, UGA, with UAG or UAA in atnaC-stop codon-tnaA′-′lacZ reporter construct. Basal level expression was reduced to 20 and 50% when the UGA stop codon was replaced by UAG or UAA, respectively, consistent with the finding that in E. coli translation terminates more efficiently at UAG and UAA than at UGA. Tryptophan induction was observed in strains with any of the stop codons. However, when UAG or UAA replaced UGA, the induced level of expression was also reduced to 15 and 50% of that obtained with UGA as the tnaC stop codon, respectively. Introduction of a mutant allele encoding a temperature-sensitive release factor 1, prfA1, increased basal level expression 60-fold when the tnaC stop codon was UAG and 3-fold when this stop codon was UAA; basal level expression was reduced by 50% in the construct with the natural stop codon, UGA. In strains with any of the three stop codons and the prfA1mutation, the induced levels of tna operon expression were virtually identical. The effects of tnaC stop codon identity on expression were also examined in the absence of Rho action, using tnaC-stop codon-′lacZ constructs that lack the tnaC-tnaA spacer region. Expression was low in the absence of tnaC stop codon suppression. In most cases, tryptophan addition resulted in about 50% inhibition of expression when UGA was replaced by UAG or UAA and the appropriate suppressor was present. Introduction of the prfA1 mutant allele increased expression of the suppressed construct with the UAG stop codon; tryptophan addition also resulted in ca. 50% inhibition. These findings provide additional evidence implicating the behavior of the ribosome translating tnaC in the regulation of tna operon expression.
4
Tovey, Hilary. "Book Review: Comparison of the Campaigns for Raidio na Gaeltachta and TnaG." Irish Journal of Sociology 11, no. 2 (November 2002): 147–49. http://dx.doi.org/10.1177/079160350201100209.
5
Konan, Kouacou Vincent, and Charles Yanofsky. "Rho-Dependent Transcription Termination in the tnaOperon of Escherichia coli: Roles of the boxASequence and the rut Site." Journal of Bacteriology 182, no. 14 (July 15, 2000): 3981–88. http://dx.doi.org/10.1128/jb.182.14.3981-3988.2000.
Анотація:
ABSTRACT Expression of the tryptophanase (tna) operon ofEscherichia coli is regulated by catabolite repression and by tryptophan-induced transcription antitermination. Tryptophan induction prevents Rho-dependent transcription termination in the leader region of the operon. Induction requires translation of a 24-residue leader peptide-coding region, tnaC, containing a single, crucial Trp codon. Studies with a lacZ reporter construct lacking the tnaC-tnaA spacer region suggest that, in the presence of excess tryptophan, the TnaC leader peptide acts incis on the ribosome translating tnaC to inhibit its release. The stalled ribosome is thought to block Rho's access to the transcript. In this paper we examine the roles of theboxA sequence and the rut site in Rho-dependent termination. Deleting six nucleotides (CGC CCT) of boxA or introducing specific point mutations in boxA results in high-level constitutive expression. Some constitutive changes introduced in boxA do not change the TnaC peptide sequence. We confirm that deletion of the rut site results in constitutive expression. We also demonstrate that, in each constitutive construct, replacement of the tnaC start codon by a UAG stop codon reduces expression significantly, suggesting that constitutive expression requires translation of the tnaCcoding sequence. Addition of bicyclomycin, an inhibitor of Rho, to these UAG constructs increases expression, demonstrating that reduced expression is due to Rho action. Combining a boxA point mutation with rut site deletion results in constitutive expression comparable to that of a maximally induced operon. These results support the hypothesis that in the presence of tryptophan the ribosome translating tnaC blocks Rho's access to theboxA and rut sites, thereby preventing transcription termination.
6
Almansour, Haidara, Johann Jacoby, Heiko Baumgartner, Marie K. Reumann, Konstantin Nikolaou, and Fabian Springer. "Injury of the Tibial Nutrient Artery Canal during External Fixation for Lower Extremity Fractures: A Computed Tomography Study." Journal of Clinical Medicine 9, no. 7 (July 14, 2020): 2235. http://dx.doi.org/10.3390/jcm9072235.
Анотація:
The tibial nutrient artery (TNA) is the major diaphyseal artery of the tibia supplying two thirds of the inner osseous cortex. Hence, iatrogenic injury of the TNA endangers the integrity of the tibial blood supply and may compromise fracture healing. The incidence of its injury in the setting of external fixation for lower limb fractures has not been previously investigated. The aim of this study was to evaluate the incidence of TNA injury in the context of external fixation and to characterize the topography of the fixator pins in relation to the TNA canal (TNAC). Patients who underwent external fixation for distal femoral fractures and for tibial (proximal, shaft, and distal) fractures and had a postoperative computed tomography study were retrospectively included. The following parameters were retrieved: 1) Pin characteristics (orientation and cortical position of the pins), 2) The anatomic relationship between the TNAC and external fixation pin (topography above/below and at the level of the TNAC, and the distance between the pin and medial tibial plateau and/or the medial malleolus), and 3) The incidence of TNAC injury (complete/partial disruption of TNA lumen). A total of 105 patients with 214 tibial pins were analyzed. In 27 patients (26%), the TNAC was completely injured by the pins of the external fixator. In 13 patients (12%), the TNAC was partially injured. Of the 214 analyzed pins, 85 pins (40%) were located at the level of the TNAC (the TNAC and the pin are seen on the same axial slice). Most pins that were applied at the level of the TNAC belonged to a knee-bridging external fixator. Of those, ninety-three percent of the pins were anteromedially applied according to published surgical guidelines. Six percent of the pins were applied through the tibial crest and 1% anterolaterally. Of those 85 pins, 42 pins (49%) injured the TNAC at least partially. Based on the analyzed pins and the incidence of partial and complete injury of the TNAC, we observed that the tibial segment at which the tibial nutrient artery is endangered was located approximately (95% CI: 13–15 cm) from the medial tibia plateau and (95% CI: 22–25 cm) from the medial malleolus. Thus, TNAC injury by external fixation pins in the context of lower limb fractures can be considered common. Almost half of the pins applied at the middle third of the tibia injured the TNA, despite adherence to published surgical guidelines for external fixation. When possible, pin application at the middle third of tibia should be avoided to circumvent iatrogenic injury of the TNA and to safeguard tibial blood supply.
7
Manicardi, G. C., D. Bizzaro, E. Galli, and U. Bianchi. "Heterochromatin heterogeneity in the holocentric X chromatin of Megoura viciae (Homoptera, Aphididae)." Genome 39, no. 2 (April 1, 1996): 465–70. http://dx.doi.org/10.1139/g96-059.
Анотація:
Holocentric chromosomes, prepared by spreading embryo cells obtained from Megoura viciae parthenogenetic females, have been C-banded, enzymatically digested in situ using the specific endonucleases DdeI (C↓TNAG), DraI (TTT↓AAA), Tru9I (TT↓AA), and CfoI (GCG↓C), and subsequently stained with Giemsa, DAPI, CMA3, and AgNO3. We observed that the X chromosome had the best defined banding patterns. In the M. viciae X chromosome there is a certain amount of heterogeneity in heterochromatic DNA composition. In fact, the GC-rich NOR-associated heterochromatin differs from other heterochromatic bands that are characterized by AT-rich DNAs. Our data also indicate that, in M. viciae holocentric chromosomes, all heterochromatic blocks are accessible to in situ enzyme attack, the only limit to the digestion being the presence or absence of recognition targets. This is an interesting point, since, in monocentric chromosomes, it is well known that in situ endonuclease digestion is heavily affected not only by DNA base composition but also by chromatin compactness that may limit enzyme accessibility to their specific targets. Key words : heterochromatin, holocentric chromosomes, aphids.
8
Cruz-Vera, Luis R., and Charles Yanofsky. "Conserved Residues Asp16 and Pro24 of TnaC-tRNAPro Participate in Tryptophan Induction of tna Operon Expression." Journal of Bacteriology 190, no. 14 (April 18, 2008): 4791–97. http://dx.doi.org/10.1128/jb.00290-08.
Анотація:
ABSTRACT In Escherichia coli, interactions between the nascent TnaC-tRNAPro peptidyl-tRNA and the translating ribosome create a tryptophan binding site in the ribosome where bound tryptophan inhibits TnaC-tRNAPro cleavage. This inhibition delays ribosome release, thereby inhibiting Rho factor binding and action, resulting in increased tna operon transcription. Replacing Trp12 of TnaC with any other amino acid residue was previously shown to prevent tryptophan binding and induction of tna operon expression. Genome-wide comparisons of TnaC amino acid sequences identify Asp16 and Pro24, as well as Trp12, as highly conserved TnaC residues. Replacing these residues with other residues was previously shown to influence tryptophan induction of tna operon expression. In this study, in vitro analyses were performed to examine the potential roles of Asp16 and Pro24 in tna operon induction. Replacing Asp16 or Pro24 of TnaC of E. coli with other amino acids established that these residues are essential for free tryptophan binding and inhibition of TnaC-tRNAPro cleavage at the peptidyl transferase center. Asp16 and Pro24 are in fact located in spatial positions corresponding to critical residues of AAP, another ribosome regulatory peptide. Sparsomycin-methylation protection studies further suggested that segments of 23S RNA were arranged differently in ribosomes bearing TnaCs with either the Asp16Ala or the Pro24Ala change. Thus, features of the amino acid sequence of TnaC of the nascent TnaC-tRNAPro peptidyl-tRNA, in addition to the presence of Trp12, are necessary for the nascent peptide to create a tryptophan binding/inhibition site in the translating ribosome.
9
Cruz-Vera, Luis R., Rui Yang, and Charles Yanofsky. "Tryptophan Inhibits Proteus vulgaris TnaC Leader Peptide Elongation, Activating tna Operon Expression." Journal of Bacteriology 191, no. 22 (September 18, 2009): 7001–6. http://dx.doi.org/10.1128/jb.01002-09.
Анотація:
ABSTRACT Expression of the tna operon of Escherichia coli and of Proteus vulgaris is induced by l-tryptophan. In E. coli, tryptophan action is dependent on the presence of several critical residues (underlined) in the newly synthesized TnaC leader peptide, WFNIDXXL/IXXXXP. These residues are conserved in TnaC of P. vulgaris and of other bacterial species. TnaC of P. vulgaris has one additional feature, distinguishing it from TnaC of E. coli; it contains two C-terminal lysine residues following the conserved proline residue. In the present study, we investigated l-tryptophan induction of the P. vulgaris tna operon, transferred on a plasmid into E. coli. Induction was shown to be l-tryptophan dependent; however, the range of induction was less than that observed for the E. coli tna operon. We compared the genetic organization of both operons and predicted similar folding patterns for their respective leader mRNA segments. However, additional analyses revealed that l-tryptophan action in the P. vulgaris tna operon involves inhibition of TnaC elongation, following addition of proline, rather than inhibition of leader peptide termination. Our findings also establish that the conserved residues in TnaC of P. vulgaris are essential for l-tryptophan induction, and for inhibition of peptide elongation. TnaC synthesis is thus an excellent model system for studies of regulation of both peptide termination and peptide elongation, and for studies of ribosome recognition of the features of a nascent peptide.
10
Gong, Ming, Luis R. Cruz-Vera, and Charles Yanofsky. "Ribosome Recycling Factor and Release Factor 3 Action Promotes TnaC-Peptidyl-tRNA Dropoff and Relieves Ribosome Stalling during Tryptophan Induction of tna Operon Expression in Escherichia coli." Journal of Bacteriology 189, no. 8 (February 9, 2007): 3147–55. http://dx.doi.org/10.1128/jb.01868-06.
Анотація:
ABSTRACT Upon tryptophan induction of tna operon expression in Escherichia coli, the leader peptidyl-tRNA, TnaC- \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(tRNA_{2}^{Pro}\) \end{document} , resists cleavage, resulting in ribosome stalling at the tnaC stop codon. This stalled ribosome blocks Rho factor binding and action, preventing transcription termination in the tna operon's leader region. Plasmid-mediated overexpression of tnaC was previously shown to inhibit cell growth by reducing uncharged \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(tRNA_{2}^{Pro}\) \end{document} availability. Which factors relieve ribosome stalling, facilitate TnaC- \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(tRNA_{2}^{Pro}\) \end{document} cleavage, and relieve growth inhibition were addressed in the current study. In strains containing the chromosomal tna operon and lacking a tnaC plasmid, the overproduction of ribosome recycling factor (RRF) and release factor 3 (RF3) reduced tna operon expression. Their overproduction in vivo also increased the rate of cleavage of TnaC- \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(tRNA_{2}^{Pro}\) \end{document} , relieving the growth inhibition associated with plasmid-mediated tnaC overexpression. The overproduction of elongation factor G or initiation factor 3 did not have comparable effects, and tmRNA was incapable of attacking TnaC- \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(tRNA_{2}^{Pro}\) \end{document} in stalled ribosome complexes. The stability of TnaC- \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(tRNA_{2}^{Pro}\) \end{document} was increased appreciably in strains deficient in RRF and RF3 or deficient in peptidyl-tRNA hydrolase. These findings reveal the existence of a natural mechanism whereby an amino acid, tryptophan, binds to ribosomes that have just completed the synthesis of TnaC- \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(tRNA_{2}^{Pro}\) \end{document} . Bound tryptophan inhibits RF2-mediated cleavage of TnaC- \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(tRNA_{2}^{Pro}\) \end{document} , resulting in the stalling of the ribosome translating tnaC mRNA. This stalling results in increased transcription of the structural genes of the tna operon. RRF and RF3 then bind to this stalled ribosome complex and slowly release TnaC- \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(tRNA_{2}^{Pro}\) \end{document} . This release allows ribosome recycling and permits the cleavage of TnaC- \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(tRNA_{2}^{Pro}\) \end{document} by peptidyl-tRNA hydrolase.
11
Ren, Yanyu, Xiumin Shi, Pengcheng Xia, Shuang Li, Mingyang Lv, Yunxin Wang, and Zhu Mao. "In Situ Raman Investigation of TiO2 Nanotube Array-Based Ultraviolet Photodetectors: Effects of Nanotube Length." Molecules 25, no. 8 (April 17, 2020): 1854. http://dx.doi.org/10.3390/molecules25081854.
Анотація:
TiO2 nanotube arrays (TNAs) with tube lengths of 4, 6, and 7 μm were prepared via two-step anodization. Thereafter, ultraviolet (UV) photodetectors (PDs) with Au/TiO2/Au structures were prepared using these TNAs with different tube lengths. The effects of TNA length and device area on the performance of the device were investigated using in situ Raman spectroscopy. The maximum laser/dark current ratio was achieved by using a TNA with a size of 1 × 1 cm2 and a length of 7 μm, under a 532 nm laser. In addition, when the device was irradiated with a higher energy laser (325 nm), the UV Raman spectrum was found to be more sensitive than the visible Raman spectrum. At 325 nm, the laser/dark current ratio was nearly 24 times higher than that under a 532 nm laser. Six phonon modes of anatase TNAs were observed, at 144, 199, 395, 514, and 635 cm−1, which were assigned to the Eg(1), Eg(2), B1g(1), A1g/B1g(2), and Eg(3) modes, respectively. The strong low-frequency band at 144 cm−1 was caused by the O-Ti-O bending vibration and is a characteristic band of anatase. The results show that the performance of TNA-based PDs is length-dependent. Surface-enhanced Raman scattering signals of 4-mercaptobenzoic acid (4-MBA) molecules were also observed on the TNA surface. This result indicates that the length-dependent performance may be derived from an increase in the specific surface area of the TNA. In addition, the strong absorption of UV light by the TNAs caused a blueshift of the Eg(1) mode.
12
Tallberg, Jonas, Thomas Sommerer, Theresa Squatrito, and Christer Jönsson. "Explaining the Transnational Design of International Organizations." International Organization 68, no. 4 (2014): 741–74. http://dx.doi.org/10.1017/s0020818314000149.
Анотація:
AbstractPast decades have witnessed a shift in international cooperation toward growing involvement of transnational actors (TNAs), such as nongovernmental organizations, multinational corporations, and philanthropic foundations. This article offers a comprehensive theoretical and empirical account of TNA access to IOs. The analysis builds on a novel data set, covering formal TNA access to 298 organizational bodies from fifty IOs over the time period 1950 to 2010. We identify the most profound patterns in TNA access across time, issue areas, policy functions, and world regions, and statistically test competing explanations of the variation in TNA access. The central results are three-fold. First, the empirical data confirm the existence of a far-reaching institutional transformation of IOs over the past sixty years, pervading all issue areas, policy functions, and world regions. Second, variation in TNA access within and across IOs is mainly explained by a combination of three factors: functional demand for the resources of TNAs, domestic democratic standards in the membership of IOs, and state concerns with national sovereignty. Third, existing research suffers from a selection bias that has led it to overestimate the general importance of a new participatory norm in global governance for the openness of IOs.
13
Cruz-Vera, Luis R., Aaron New, Catherine Squires, and Charles Yanofsky. "Ribosomal Features Essential for tna Operon Induction: Tryptophan Binding at the Peptidyl Transferase Center." Journal of Bacteriology 189, no. 8 (February 9, 2007): 3140–46. http://dx.doi.org/10.1128/jb.01869-06.
Анотація:
ABSTRACT Features of the amino acid sequence of the TnaC nascent peptide are recognized by the translating ribosome. Recognition leads to tryptophan binding within the translating ribosome, inhibiting the termination of tnaC translation and preventing Rho-dependent transcription termination in the tna operon leader region. It was previously shown that inserting an adenine residue at position 751 or introducing the U2609C change in 23S rRNA or introducing the K90W replacement in ribosomal protein L22 prevented tryptophan induction of tna operon expression. It was also observed that an adenine at position 752 of 23S rRNA was required for induction. In the current study, the explanation for the lack of induction by these altered ribosomes was investigated. Using isolated TnaC-ribosome complexes, it was shown that although tryptophan inhibits puromycin cleavage of TnaC-tRNAPro with wild-type ribosome complexes, it does not inhibit cleavage with the four mutant ribosome complexes examined. Similarly, tryptophan prevents sparsomycin inhibition of TnaC-tRNAPro cleavage with wild-type ribosome complexes but not with these mutant ribosome complexes. Additionally, a nucleotide located close to the peptidyl transferase center, A2572, which was protected from methylation by tryptophan with wild-type ribosome complexes, was not protected with mutant ribosome complexes. These findings identify specific ribosomal residues located in the ribosome exit tunnel that recognize features of the TnaC peptide. This recognition creates a free tryptophan-binding site in the peptidyl transferase center, where bound tryptophan inhibits peptidyl transferase activity.
14
D'Angio, Richard G., Karen C. Riechers, Robert B. Gilsdorf, and John M. Constantino. "Effect of the Mode of Lipid Administration on Parenteral Nutrition-Related Infections." Annals of Pharmacotherapy 26, no. 1 (January 1992): 14–17. http://dx.doi.org/10.1177/106002809202600103.
Анотація:
OBJECTIVE: To determine if total nutrient admixtures (TNAs) influence the rate of infection in clinical practice. DESIGN: Prospective, randomized trial. SETTING: Department of Veterans Affairs Medical Center. PATIENTS: All patients were administered parenteral nutrition (PN) via a central venous catheter and received daily lipids. INTERVENTION: Patients were randomized as to the mode of administration of lipids. Lipids were either administered with other PN components in a TNA or were piggybacked (PB) into the PN solution. MAIN OUTCOME MEASURES: Treatment groups were compared for the rate of occurrence of PN-related infections. Infections were classified as catheter infections or catheter sepsis. RESULTS: Ninety-eight patients were entered into the trial. Data from % patients (44 TNA, 52 PB) were available for analysis. Treatment groups were well matched for age, baseline albumin, days of PN, predicted basal metabolic rate, and calorie and protein requirements. TNA patients received a significantly greater percentage of nonprotein calories as lipid. The incidence of infection was 12.6 and 10.3 per 1000 days of PN in the TNA and PB groups, respectively (p=0.89). The microorganisms responsible for infection and the type of infections that developed were similar in both groups. CONCLUSIONS: Use of TNAs does not influence the rate of infection in patients receiving PN.
15
Bernasconi, Camilla, Giorgio Volponi, Claudia Picozzi, and Roberto Foschino. "Use of the tna Operon as a New Molecular Target for Escherichia coli Detection." Applied and Environmental Microbiology 73, no. 19 (August 10, 2007): 6321–25. http://dx.doi.org/10.1128/aem.00606-07.
Анотація:
ABSTRACT A quantitative real-time PCR targeting the tnaA gene was studied to detect Escherichia coli and distinguish E. coli from Shigella spp. These microorganisms revealed high similarity in the molecular organization of the tna operon.
16
Yang, Rui, Luis R. Cruz-Vera, and Charles Yanofsky. "23S rRNA Nucleotides in the Peptidyl Transferase Center Are Essential for Tryptophanase Operon Induction." Journal of Bacteriology 191, no. 11 (March 27, 2009): 3445–50. http://dx.doi.org/10.1128/jb.00096-09.
Анотація:
ABSTRACT Distinct features of the ribosomal peptide exit tunnel are known to be essential for recognition of specific amino acids of a nascent peptidyl-tRNA. Thus, a tryptophan residue at position 12 of the peptidyl-tRNA TnaC-tRNAPro leads to the creation of a free tryptophan binding site within the ribosome at which bound tryptophan inhibits normal ribosome functions. The ribosomal processes that are inhibited are hydrolysis of TnaC-tRNAPro by release factor 2 and peptidyl transfer of TnaC of TnaC-tRNAPro to puromycin. These events are normally performed in the ribosomal peptidyl transferase center. In the present study, changes of 23S rRNA nucleotides in the 2585 region of the peptidyl transferase center, G2583A and U2584C, were observed to reduce maximum induction of tna operon expression by tryptophan in vivo without affecting the concentration of tryptophan necessary to obtain 50% induction. The growth rate of strains with ribosomes with either of these changes was not altered appreciably. In vitro analyses with mutant ribosomes with these changes showed that tryptophan was not as efficient in protecting TnaC-tRNAPro from puromycin action as wild-type ribosomes. However, added tryptophan did prevent sparsomycin action as it normally does with wild-type ribosomes. These findings suggest that these two mutational changes act by reducing the ability of ribosome-bound tryptophan to inhibit peptidyl transferase activity rather than by reducing the ability of the ribosome to bind tryptophan. Thus, the present study identifies specific nucleotides within the ribosomal peptidyl transferase center that appear to be essential for effective tryptophan induction of tna operon expression.
17
Gong, Ming, Feng Gong, and Charles Yanofsky. "Overexpression of tnaC of Escherichia coli Inhibits Growth by Depleting tRNA2Pro Availability." Journal of Bacteriology 188, no. 5 (March 1, 2006): 1892–98. http://dx.doi.org/10.1128/jb.188.5.1892-1898.2006.
Анотація:
ABSTRACT Transcription of the tryptophanase (tna) operon of Escherichia coli is regulated by catabolite repression and tryptophan-induced transcription antitermination. Induction results from ribosome stalling after translation of tnaC, the coding region for a 24-residue leader peptide. The last sense codon of tnaC, proline codon 24 (CCU), is translated by tRNA2 Pro. We analyzed the consequences of overexpression of tnaC from a multicopy plasmid and observed that under inducing conditions more than 60% of the tRNA2 Pro in the cell was sequestered in ribosomes as TnaC-tRNA2 Pro. The half-life of this TnaC-tRNA2 Pro was shown to be 10 to 15 min under these conditions. Plasmid-mediated overexpression of tnaC, under inducing conditions, reduced cell growth rate appreciably. Increasing the tRNA2 Pro level relieved this growth inhibition, suggesting that depletion of this tRNA was primarily responsible for the growth rate reduction. Growth inhibition was not relieved by overexpression of tRNA1 Pro, a tRNAPro that translates CCG, but not CCU. Replacing the Pro24CCU codon of tnaC by Pro24CCG, a Pro codon translated by tRNA1 Pro, also led to growth rate reduction, and this reduction was relieved by overexpression of tRNA1 Pro. These findings establish that the growth inhibition caused by tnaC overexpression during induction by tryptophan is primarily a consequence of tRNAPro depletion, resulting from TnaC-tRNAPro retention within stalled, translating ribosomes.
18
Dzmitruk, Volha, Evgeny Apartsin, Aliaksei Ihnatsyeu-Kachan, Viktar Abashkin, Dzmitry Shcharbin, and Maria Bryszewska. "Dendrimers Show Promise for siRNA and microRNA Therapeutics." Pharmaceutics 10, no. 3 (August 8, 2018): 126. http://dx.doi.org/10.3390/pharmaceutics10030126.
Анотація:
The lack of an appropriate intracellular delivery system for therapeutic nucleic acids (TNAs) is a major problem in molecular biology, biotechnology, and medicine. A relatively new class of highly symmetrical hyperbranched polymers, called dendrimers, shows promise for transporting small TNAs into both cells and target tissues. Dendrimers have intrinsic advantages for this purpose: their physico-chemical and biological properties can be controlled during synthesis, and they are able to transport large numbers of TNA molecules that can specifically suppress the expression of single or multiple targeted genes. Numerous chemical modifications of dendrimers extend the biocompatibility of synthetic materials and allow targeted vectors to be designed for particular therapeutic purposes. This review summarizes the latest experimental data and trends in the medical application of various types of dendrimers and dendrimer-based nanoconstructions as delivery systems for short small interfering RNAs (siRNAs) and microRNAs at the cell and organism levels. It provides an overview of the structural features of dendrimers, indicating their advantages over other types of TNA transporters.
19
Oudeman, Eline A., Esther E. Bron, Renske M. Van den Berg-Vos, Jacoba P. Greving, Geert Jan Biessels, Catharina J. M. Klijn, and L. Jaap Kappelle. "Cerebral Perfusion and the Occurrence of Nonfocal Transient Neurological Attacks." Cerebrovascular Diseases 47, no. 5-6 (2019): 303–8. http://dx.doi.org/10.1159/000502334.
Анотація:
Introduction: Nonfocal transient neurological attacks (TNAs) are associated with an increased risk of cardiac events, stroke and dementia. Their etiology is still unknown. Global cerebral hypoperfusion has been suggested to play a role in their etiology, but this has not been investigated. We assessed whether lower total brain perfusion is associated with a higher occurrence of TNAs. Methods: Between 2015 and 2018, patients with heart failure were included in the Heart Brain Connection study. Patients underwent brain magnetic resonance imaging, including quantitative magnetic resonance angiography (QMRA) to measure cerebral blood flow (CBF). We calculated total brain perfusion of each participant by dividing total CBF by brain volume. Patients were interviewed with a standardized questionnaire on the occurrence of TNAs by physicians who were blinded to QMRA flow status. We assessed the relation between total brain perfusion and the occurrence of TNAs with Poisson regression analysis. Results: Of 136 patients (mean age 70 years, 68% men), 29 (21%) experienced ≥1 TNAs. Nonrotatory dizziness was the most common subtype of TNA. Patients with TNAs were more often female and more often had angina pectoris than patients without TNAs, but total CBF and total brain perfusion were not different between both groups. Total brain perfusion was not associated with the occurrence of TNAs (adjusted risk ratio 1.12, 95% CI 0.88–1.42). Conclusion: We found no association between total brain perfusion and the occurrence of TNAs in patients with heart failure.
20
Liu, Min-Hsien, Cheng Chen, and Yaw-Shun Hong. "Theoretical study of the unimolecular decomposition mechanisms of energetic TNAD and TNAZ explosives." International Journal of Quantum Chemistry 102, no. 4 (2005): 398–408. http://dx.doi.org/10.1002/qua.20284.
21
Oudeman, Eline A., Eline J. Volkers, Jacoba P. Greving, Catharina JM Klijn, Ale Algra, and L. Jaap Kappelle. "Nonfocal transient neurological attacks in patients with carotid artery occlusion." European Stroke Journal 4, no. 1 (December 12, 2018): 50–54. http://dx.doi.org/10.1177/2396987318818779.
Анотація:
Introduction Nonfocal transient neurological attacks (TNAs) are episodes with atypical, nonlocalizing cerebral symptoms. We examined the prevalence of nonfocal TNAs, in patients with and without carotid artery occlusion (CAO). Methods We included 67 patients with CAO and 62 patients without CAO. In both groups, patients had a history of transient ischemic attack (TIA) or nondisabling ischemic stroke in the anterior circulation that had occurred >6 months before inclusion. Patients without CAO did not have ipsilateral or contralateral carotid artery stenosis of ≥50%. All patients were interviewed with a standardized questionnaire on the occurrence of nonfocal TNA symptoms during the preceding six months. We calculated risk ratios (RRs) with 95% confidence intervals (CIs) for the occurrence of ≥1 and ≥2 different nonfocal TNAs after adjustments for age, sex, systolic blood pressure and time interval between most recent TIA or ischemic stroke and administration of the questionnaire. Results Forty-three of all patients (33%) had had one or more nonfocal TNAs in the preceding six months. Nonrotatory dizziness (24%) was reported most often. The prevalence of ≥1 nonfocal TNAs was not significantly different between patients with and without CAO (39% vs. 27%; adjusted RR 1.47, 95% CI 0.83–2.61), but the prevalence of ≥2 or more different nonfocal TNAs was higher in patients with CAO (16% vs. 3%; adjusted RR 4.77, 95% CI 1.20–18.98). In patients with CAO who also had a contralateral carotid or vertebral artery steno-occlusion, nonfocal TNAs occurred more often than in patients without any carotid or vertebral artery steno-occlusion (46% vs. 27%; adjusted RR 2.22, 95% CI 1.08–4.60 for ≥1 and 21% vs. 3%; adjusted RR 8.27, 95% CI 1.83–37.32 for ≥2 nonfocal TNAs). Conclusions Patients with CAO more often experienced multiple nonfocal TNAs than patients without CAO.
22
Łętocha, Aneta, Daniel Toboła, and Tatiana Miller. "Surface topography analysis of Vanadis 6 tool steel after selected sequential surface treatment processes." Mechanik 91, no. 12 (December 10, 2018): 1124–28. http://dx.doi.org/10.17814/mechanik.2018.12.200.
Анотація:
Issues related with an influence of selected sequential surface treatment processes on the stereometric features of the formed surface layer (SL) of Vanadis 6 steel are presented. Some variants of machining include: turning (T), turning–burnishing (TN), turning–burnishing–nitriding (TNA), turning–burnishing–sulfonitriding (TNAS) and turning–burnishing–PVD coating (TNPVD). Studies were carried out by contact profiling method with use TOPO 01P device – produced by The Institute of Advanced Manufacturing Technology. Qualitative changes in the graphs of examined surfaces and also changes in the results of surface roughness parameters and profile were analyzed.
23
Bai, Long, Peiru Chen, Bin Tang, Ruiqiang Hang, and Yin Xiao. "Correlation between LncRNA Profiles in the Blood Clot Formed on Nano-Scaled Implant Surfaces and Osseointegration." Nanomaterials 11, no. 3 (March 9, 2021): 674. http://dx.doi.org/10.3390/nano11030674.
Анотація:
Implant surfaces with a nanoscaled pattern can dominate the blood coagulation process resulting in a defined clot structure and its degradation behavior, which in turn influence cellular response and the early phase of osseointegration. Long non-coding (Lnc) RNAs are known to regulate many biological processes in the skeletal system; however, the link between the LncRNA derived from the cells within the clot and osseointegration has not been investigated to date. Hence, the sequence analysis of LncRNAs expressed within the clot formed on titania nanotube arrays (TNAs) with distinct nano-scaled diameters (TNA 15 of 15 nm, TNA 60 of 60 nm, TNA 120 of 120 nm) on titanium surfaces was profiled for the first time. LncRNA LOC103346307, LOC103352121, LOC108175175, LOC103348180, LOC108176660, and LOC108176465 were identified as the pivotal players in the early formed clot on the nano-scaled surfaces. Further bioinformatic prediction results were used to generate co-expression networks of LncRNAs and mRNAs. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses revealed that distinct nano-scaled surfaces could regulate the biological functions of target mRNAs in the clot. LOC103346307, LOC108175175, and LOC108176660 upregulated mRNAs related to cell metabolism and Wnt, TGF-beta, and VEGF signaling pathways in TNA 15 compared with P-Ti, TNA 60, and TNA 120, respectively, whereas LOC103352121, LOC103348180, and LOC108176465 downregulated mRNAs related to bone resorption and inflammation through negatively regulating osteoclast differentiation, TNF, and NF-kappa signaling pathways. The results indicated that surface nano-scaled characteristics can significantly influence the clot-derived LncRNAs expression profile, which affects osseointegration through multiple signaling pathways of the targeted mRNAs, thus paving a way for better interpreting the link between the properties of a blood clot formed on the nano-surface and de novo bone formation.
24
Gilbert, Francis, Jacques E. Leclerc, Marianne Deschênes, Anne-Sophie Julien, and Iseult Grenier-Ouellette. "Furlow Palatoplasty, Nasopharyngeal Size, and Sleep Oximetry." Cleft Palate-Craniofacial Journal 57, no. 7 (February 11, 2020): 819–27. http://dx.doi.org/10.1177/1055665619900865.
Анотація:
Objectives: (1) To assess the evolution of prepalatoplasty sleep oximetry (PRESO) and postpalatoplasty sleep oximetry (POSSO) in cleft patients and (2) to evaluate the impact of the size of the nasopharynx on PRESO and POSSO values. Study Design: Retrospective cohort study. Patients and Methods: In 81 patients with cleft palate and/or cleft lip, the following data were prospectively collected: patient demographics and prepalatoplasty cleft palate measurements. All the patients had at least 1 PRESO and POSSO. A Kaplan-Meier curve was obtained from all the sleep oximetry results. Transverse nasopharyngeal area (TNA) pre- and postvalues were compared for each group with paired t tests, while analysis of variance was used to compare TNA pre- and postscores between the groups with a Bonferroni correction for multiple comparisons. Results: POSSO results were normal or showed mild desaturations in most patients in the few weeks following palatoplasty. For the cohort, no statistically significant changes were found between PRESO and POSSO values. A 2-fold variation in the area of the TNA was found before palatoplasty within identical cleft malformation cases. No statistically significant association was found between the TNA or the a/30 − b 1 parameter values and the sleep study scores. Conclusions: The patients with the smaller nasopharyngeal areas presented identical PRESO and POSSO results when compared to those with larger nasopharyngeal sizes. Future studies should address the possible association between prepalatoplasty and postpalatoplasty TNAs and the occurrence of velopharyngeal deficiency later in life.
25
Konan, K. V., and C. Yanofsky. "Regulation of the Escherichia coli tna operon: nascent leader peptide control at the tnaC stop codon." Journal of bacteriology 179, no. 5 (1997): 1774–79. http://dx.doi.org/10.1128/jb.179.5.1774-1779.1997.
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Lu, Hang, Jason Catania, Katalin Baranji, Jie Feng, Mili Gu, Janet Lathey, Diane Sweeny, et al. "Characterization of the Native Form of Anthrax Lethal Factor for Use in the Toxin Neutralization Assay." Clinical and Vaccine Immunology 20, no. 7 (May 1, 2013): 986–97. http://dx.doi.org/10.1128/cvi.00046-13.
Анотація:
ABSTRACTThe cell-based anthrax toxin neutralization assay (TNA) is used to determine functional antibody titers of sera from animals and humans immunized with anthrax vaccines. The anthrax lethal toxin is a critical reagent of the TNA composed of protective antigen (PA) and lethal factor (LF), which are neutralization targets of serum antibodies. Cytotoxic potency of recombinant LF (rLF) lots can vary substantially, causing a challenge in producing a renewable supply of this reagent for validated TNAs. To address this issue, we characterized a more potent rLF variant (rLF-A) with the exact native LF amino acid sequence that lacks the additional N-terminal histidine and methionine residues present on the commonly used form of rLF (rLF-HMA) as a consequence of the expression vector. rLF-A can be used at 4 to 6 ng/ml (in contrast to 40 ng/ml rLF-HMA) with 50 ng/ml recombinant PA (rPA) to achieve 95 to 99% cytotoxicity. In the presence of 50 ng/ml rPA, both rLF-A and rLF-HMA allowed for similar potencies (50% effective dilution) among immune sera in the TNA. rPA, but not rLF, was the dominant factor in determining potency of serum samples containing anti-PA antibodies only or an excess of anti-PA relative to anti-rLF antibodies. Such anti-PA content is reflected in immune sera derived from most anthrax vaccines in development. These results support that 7- to 10-fold less rLF-A can be used in place of rLF-HMA without changing TNA serum dilution curve parameters, thus extending the use of a single rLF lot and a consistent, renewable supply.
27
Kwon, Young-Man, and Bernard Weiss. "Production of 3-Nitrosoindole Derivatives by Escherichia coli during Anaerobic Growth." Journal of Bacteriology 191, no. 17 (June 26, 2009): 5369–76. http://dx.doi.org/10.1128/jb.00586-09.
Анотація:
ABSTRACT When Escherichia coli K-12 is grown anaerobically in medium containing tryptophan and sodium nitrate, it produces red compounds. The reaction requires functional genes for trytophanase (tnaA), a tryptophan permease (tnaB), and a nitrate reductase (narG), as well as a natural drop in the pH of the culture. Mass spectrometry revealed that the purified chromophores had mass/charge ratios that closely match those for indole red, indoxyl red, and an indole trimer. These compounds are known products of chemical reactions between indole and nitrous acid. They are derived from an initial reaction of 3-nitrosoindole with indole. Apparently, nitrite that is produced from the metabolic reduction of nitrate is converted in the acid medium to nitrous acid, which leads to the nitrosation of the indole that is generated by tryptophanase. An nfi (endonuclease V) mutant and a recA mutant were selectively killed during the period of chromophore production, and a uvrA strain displayed reduced growth. These effects depended on the addition of nitrate to the medium and on tryptophanase activity in the cells. Unexpectedly, the killing of a tnaA + nfi mutant was not accompanied by marked increases in mutation frequencies for several traits tested. The vulnerability of three DNA repair mutants indicates that a nitrosoindole or a derivative of a nitrosoindole produces lethal DNA damage.
28
Kamath, A. V., and C. Yanofsky. "Roles of the tnaC-tnaA spacer region and Rho factor in regulating expression of the tryptophanase operon of Proteus vulgaris." Journal of bacteriology 179, no. 5 (1997): 1780–86. http://dx.doi.org/10.1128/jb.179.5.1780-1786.1997.
29
Wang, Dandan, Xuedong Ding, and Philip N. Rather. "Indole Can Act as an Extracellular Signal inEscherichia coli." Journal of Bacteriology 183, no. 14 (July 15, 2001): 4210–16. http://dx.doi.org/10.1128/jb.183.14.4210-4216.2001.
Анотація:
ABSTRACT Previous work has shown that lacZ fusions to thecysK, astD, tnaB, and gabT genes inEscherichia coli are activated by self-produced extracellular signals. Using a combination of ethyl acetate extraction, reversed-phase C18 chromatography, and thin-layer chromatography, we have purified an extracellular activating signal from E. coli supernatants. Mass spectrometry revealed a molecule with an m/z peak of 117, consistent with indole. Nuclear magnetic resonance analysis of the purified E. colifactor and synthetic indole revealed identical profiles. Using synthetic indole, a dose-dependent activation was observed withlacZ fusions to the gabT, astD, andtnaB genes. However,cysK::lacZ and several control fusions were not significantly activated by indole. Conditioned medium prepared from a tnaA (tryptophanase) mutant, deficient in indole production, supported 26 to 41% lower activation of thegabT and astD fusions. The residual level of activation may be due to a second activating signal. Activation of thetnaB::lacZ fusion was reduced by greater than 70% in conditioned medium from a tnaAmutant.
30
Martin, Kimberly, Gregory Morlin, Arnold Smith, Andrea Nordyke, Abraham Eisenstark, and Miriam Golomb. "The Tryptophanase Gene Cluster of Haemophilus influenzae Type b: Evidence for Horizontal Gene Transfer." Journal of Bacteriology 180, no. 1 (January 1, 1998): 107–18. http://dx.doi.org/10.1128/jb.180.1.107-118.1998.
Анотація:
ABSTRACT Among strains of Haemophilus influenzae, the ability to catabolize tryptophan (as detected by indole production) varies and is correlated with pathogenicity. Tryptophan catabolism is widespread (70 to 75%) among harmless respiratory isolates but is nearly universal (94 to 100%) among strains causing serious disease, including meningitis. As a first step in investigating the relationship between tryptophan catabolism and virulence, we have identified genes in pathogenic H. influenzae which are homologous to the tryptophanase (tna) operon of Escherichia coli. The tna genes are located on a 3.1-kb fragment betweennlpD and mutS in the H. influenzaetype b (Eagan) genome, are flanked by 43-bp direct repeats of an uptake signal sequence downstream from nlpD, and appear to have been inserted as a mobile unit within this sequence. The organization of this insertion is reminiscent of pathogenicity islands. Thetna cluster is found at the same map location in all indole-positive strains of H. influenzae surveyed and is absent from reference type d and e genomes. In contrast to H. influenzae, most other Haemophilus species lacktna genes. Phylogenetic comparisons suggest that thetna cluster was acquired by intergeneric lateral transfer, either by H. influenzae or a recent ancestor, and thatE. coli may have acquired its tnaA gene from a related source. Genomes of virulent H. influenzae resemble those of pathogenic enterics in having an island of laterally transferred DNA next to mutS.
31
Do, Tho Chau Minh Vinh, Duy Quoc Nguyen, Kien Trung Nguyen, and Phuoc Huu Le. "TiO2 and Au-TiO2 Nanomaterials for Rapid Photocatalytic Degradation of Antibiotic Residues in Aquaculture Wastewater." Materials 12, no. 15 (July 31, 2019): 2434. http://dx.doi.org/10.3390/ma12152434.
Анотація:
Antibiotic residues in aquaculture wastewater are considered as an emerging environmental problem, as they are not efficiently removed in wastewater treatment plants. To address this issue, we fabricated TiO2 nanotube arrays (TNAs), TiO2 nanowires on nanotube arrays (TNWs/TNAs), Au nanoparticle (NP)-decorated-TNAs, and TNWs/TNAs, which were applied for assessing the photocatalytic degradation of eight antibiotics, simultaneously. The TNAs and TNWs/TNAs were synthesized by anodization using an aqueous NH4F/ethylene glycol solution. Au NPs were synthesized by chemical reduction method, and used to decorate on TNAs and TNWs/TNAs. All the TiO2 nanostructures exhibited anatase phase and well-defined morphology. The photocatalytic performance of TNAs, TNWs/TNAs, Au-TNAs and Au-TNWs/TNAs was studied by monitoring the degradation of amoxicillin, ampicillin, doxycycline, oxytetracycline, lincomycin, vancomycin, sulfamethazine, and sulfamethoxazole under ultraviolet (UV)-visible (VIS), or VIS illumination by LC-MS/MS method. All the four kinds of nanomaterials degraded the antibiotics effectively and rapidly, in which most antibiotics were removed completely after 20 min treatment. The Au-TNWs/TNAs exhibited the highest photocatalytic activity in degradation of the eight antibiotics. For example, reaction rate constants of Au-TNWs/TNAs for degradation of lincomycin reached 0.26 min−1 and 0.096 min−1 under UV-VIS and VIS irradiation, respectively; and they were even higher for the other antibiotics. The excellent photocatalytic activity of Au-TNWs/TNAs was attributed to the synergistic effects of: (1) The larger surface area of TNWs/TNAs as compared to TNAs, and (2) surface plasmonic effect in Au NPs to enhance the visible light harvesting.
32
Zhang, Zhi, Hwa Kyung Nam, Spencer Crouch, and Nan E. Hatch. "Tissue Nonspecific Alkaline Phosphatase Function in Bone and Muscle Progenitor Cells: Control of Mitochondrial Respiration and ATP Production." International Journal of Molecular Sciences 22, no. 3 (January 24, 2021): 1140. http://dx.doi.org/10.3390/ijms22031140.
Анотація:
Tissue nonspecific alkaline phosphatase (TNAP/Alpl) is associated with cell stemness; however, the function of TNAP in mesenchymal progenitor cells remains largely unknown. In this study, we aimed to establish an essential role for TNAP in bone and muscle progenitor cells. We investigated the impact of TNAP deficiency on bone formation, mineralization, and differentiation of bone marrow stromal cells. We also pursued studies of proliferation, mitochondrial function and ATP levels in TNAP deficient bone and muscle progenitor cells. We find that TNAP deficiency decreases trabecular bone volume fraction and trabeculation in addition to decreased mineralization. We also find that Alpl−/− mice (global TNAP knockout mice) exhibit muscle and motor coordination deficiencies similar to those found in individuals with hypophosphatasia (TNAP deficiency). Subsequent studies demonstrate diminished proliferation, with mitochondrial hyperfunction and increased ATP levels in TNAP deficient bone and muscle progenitor cells, plus intracellular expression of TNAP in TNAP+ cranial osteoprogenitors, bone marrow stromal cells, and skeletal muscle progenitor cells. Together, our results indicate that TNAP functions inside bone and muscle progenitor cells to influence mitochondrial respiration and ATP production. Future studies are required to establish mechanisms by which TNAP influences mitochondrial function and determine if modulation of TNAP can alter mitochondrial respiration in vivo.
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Johnson, K. A., L. Hessle, S. Vaingankar, C. Wennberg, S. Mauro, S. Narisawa, J. W. Goding, K. Sano, J. L. Millan, and R. Terkeltaub. "Osteoblast tissue-nonspecific alkaline phosphatase antagonizes and regulates PC-1." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 279, no. 4 (October 1, 2000): R1365—R1377. http://dx.doi.org/10.1152/ajpregu.2000.279.4.r1365.
Анотація:
Tissue-nonspecific alkaline phosphatase (TNAP) is essential for bone matrix mineralization, but the central mechanism for TNAP action remains undefined. We observed that ATP-dependent 45Ca precipitation was decreased in calvarial osteoblast matrix vesicle (MV) fractions from TNAP−/− mice, a model of infantile hypophosphatasia. Because TNAP hydrolyzes the mineralization inhibitor inorganic pyrophosphate (PPi), we assessed phosphodiesterase nucleotide pyrophosphatase (PDNP/NTPPPH) activity, which hydrolyzes ATP to generate PPi. Plasma cell membrane glycoprotein-1 (PC-1), but not the isozyme B10 (also called PDNP3) colocalized with TNAP in osteoblast MV fractions and pericellular matrix. PC-1 but not B10 increased MV fraction PPi and inhibited 45Ca precipitation by MVs. TNAP directly antagonized inhibition by PC-1 of MV-mediated 45Ca precipitation. Furthermore, the PPi content of MV fractions was greater in cultured TNAP−/− than TNAP+/+ calvarial osteoblasts. Paradoxically, transfection with wild-type TNAP significantly increased osteoblast MV fraction NTPPPH. Specific activity of NTPPPH also was twofold greater in MV fractions of osteoblasts from TNAP+/+ mice relative to TNAP−/− mice. Thus TNAP attenuates PC-1/NTPPPH-induced PPigeneration that would otherwise inhibit MV-mediated mineralization. TNAP also paradoxically regulates PC-1 expression and NTPPPH activity in osteoblasts.
34
Chen, Chia-Hung, Yen-Ping Peng, Ming-Hsun Lin, Ken-Lin Chang, Yung-Chang Lin, and Jian Sun. "Iron Modified Titanate Nanotube Arrays for Photoelectrochemical Removal of E. coli." Nanomaterials 11, no. 8 (July 28, 2021): 1944. http://dx.doi.org/10.3390/nano11081944.
Анотація:
This study used iron modified titanate nanotube arrays (Fe/TNAs) to remove E. coli in a photoelectrochemical system. The Fe/TNAs was synthesized by the anodization method and followed by the square wave voltammetry electrochemical deposition (SWVE) method with ferric nitrate as the precursor. Fe/TNAs were characterized by SEM, XRD, XPS, and UV-vis DRS to investigate the surface properties and light absorption. As a result, the iron nanoparticles (NPs) were successfully deposited on the tubular structure of the TNAs, which showed the best light utilization. Moreover, the photoelectrochemical (PEC) properties of the Fe/TNAs were measured by current-light response and electrochemical impedance spectroscopy. The photocurrent of the Fe/TNAs-0.5 (3.5 mA/cm2) was higher than TNAs (2.0 mA/cm2) and electron lifetime of Fe/TNAs-0.5 (433.3 ms) were also longer than TNAs (290.3 ms). Compared to the photolytic (P), photocatalytic (PC), and electrochemical (EC) method, Fe/TNAs PEC showed the best removal efficiency for methyl orange degradation. Furthermore, the Fe/TNAs PEC system also performed better removal efficiency than that of photolysis method in E. coli degradation experiments.
35
Do, Tho Chau Minh Vinh, Duy Quoc Nguyen, Tuan Duc Nguyen, and Phuoc Huu Le. "Development and Validation of a LC-MS/MS Method for Determination of Multi-Class Antibiotic Residues in Aquaculture and River Waters, and Photocatalytic Degradation of Antibiotics by TiO2 Nanomaterials." Catalysts 10, no. 3 (March 24, 2020): 356. http://dx.doi.org/10.3390/catal10030356.
Анотація:
This study presents a multi-residue method for simultaneous qualitative and quantitative analysis of eight antibiotics from some common classes, including beta-lactam, tetracyclines, lincosamides, glycopeptides, and sulfonamides in 39 aquaculture and river water samples from the Mekong Delta (Vietnam) using liquid chromatography-tandem mass spectrometry (LC-MS/MS). As a result, doxycycline (DXC), oxytetracycline (OTC), lincomycin (LCM), sulfamethoxazole (SMX), and sulfamethazine (SMZ) were detected with high frequency over 65% and an average concentration of 22.6–76.8 ng·mL−1. The result suggests that antibiotic residues in the aquaculture and river waters are considered as an emerging environmental problem of the region. To address this issue, we fabricated the well-defined TiO2 nanotube arrays (TNAs) and nanowires on nanotube arrays (TNWs/TNAs) using the anodization method. The TNAs had an inner tube diameter of ~95 nm and a wall thickness of ~25 nm. Meanwhile, the TNWs/TNAs had a layer of TiO2 nanowires with a length of ~6 µm partially covering the TNAs. In addition, both TNAs and TNWs/TNAs had pure anatase phase TiO2 with (101) and (112) dominant preferred orientations. Moreover, the TNAs and TNWs/TNAs effectively and rapidly degraded the antibiotic residues under UV-VIS irradiation at 120 mW/cm2 and obtained over 95% removal at 20 min. Indeed, the photocatalytic reaction rate constants (k) were in the range of 0.14–0.36 min−1 for TNAs, and 0.15–0.38 min−1 for TNWs/TNAs. Noticeably, the k values of TNWs/TNAs were slightly higher than those of TNAs for LCM, DXC, OTC, SMZ, and SMX that could be attributed to the larger surface area of TNWs/TNAs than TNAs when TNWs/TNAs had an additional ~6μm TNWs top layer.
36
Le, Phuoc, Le Hieu, Tu-Ngoc Lam, Nguyen Hang, Nguyen Truong, Le Tuyen, Pham Phong, and Jihperng Leu. "Enhanced Photocatalytic Performance of Nitrogen-Doped TiO2 Nanotube Arrays Using a Simple Annealing Process." Micromachines 9, no. 12 (November 24, 2018): 618. http://dx.doi.org/10.3390/mi9120618.
Анотація:
Nitrogen-doped TiO2 nanotube arrays (N-TNAs) were successfully fabricated by a simple thermal annealing process in ambient N2 gas at 450 °C for 3 h. TNAs with modified morphologies were prepared by a two-step anodization using an aqueous NH4F/ethylene glycol solution. The N-doping concentration (0–9.47 at %) can be varied by controlling N2 gas flow rates between 0 and 500 cc/min during the annealing process. Photocatalytic performance of as-prepared TNAs and N-TNAs was studied by monitoring the methylene blue degradation under visible light (λ ≥ 400 nm) illumination at 120 mW·cm−2. N-TNAs exhibited appreciably enhanced photocatalytic activity as compared to TNAs. The reaction rate constant for N-TNAs (9.47 at % N) reached 0.26 h−1, which was a 125% improvement over that of TNAs (0.115 h−1). The significant enhanced photocatalytic activity of N-TNAs over TNAs is attributed to the synergistic effects of (1) a reduced band gap associated with the introduction of N-doping states to serve as carrier reservoir, and (2) a reduced electron‒hole recombination rate.
37
Lin, Yuan-Chung, Chia-Hung Chen, Kang-Shin Chen, Yen-Ping Peng, Yung-Chang Lin, Shih-Wei Huang, Chien-Er Huang, Hsiao-Wu Lai, and Hsing-Wang Li. "Green Synthesized Palladium Coated Titanium Nanotube Arrays for Simultaneous Azo-Dye Degradation and Hydrogen Production." Catalysts 10, no. 11 (November 16, 2020): 1330. http://dx.doi.org/10.3390/catal10111330.
Анотація:
In this study, electrodes of titanium dioxide nanotube arrays (TNAs) were successfully synthesized by applying the anodic oxidation etching method, as well as the use of green synthetic technology to add reducing agents of tea or coffee to reduce metal palladium from palladium chloride. Synthesis of palladium modified TNAs (Pd/TNAs) was conducted by the microwave hydrothermal method after the metal palladium was reduced. In order to identify the surface structure, light absorption and elemental composition, TNAs and Pd/TNAs were characterized by X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Furthermore, to test the photocurrent density, electron resistance, and hydroxyl radicals by I-t plot, electrochemistry impedance spectroscopy (EIS), and electron paramagnetic resonance (EPR) were investigated. The photocurrent (4.0 mA/cm2) of Pd/TNAs-C (using coffee as the reducing agent) at +1.0 V (vs. Ag/AgCl) was higher than that of the pure TNAs (1.5 mA/cm2), illustrating that Pd/TNAs-C can effectively separate photogenerated electrons and holes. Pd/TNAs is a favorable material as a photoanode for the photoelectrochemical (PEC) removal of organic pollutants in wastewater.
38
Díez-Zaera, M., J. I. Díaz-Hernández, E. Hernández-Álvarez, H. Zimmermann, M. Díaz-Hernández, and M. T. Miras-Portugal. "Tissue-nonspecific alkaline phosphatase promotes axonal growth of hippocampal neurons." Molecular Biology of the Cell 22, no. 7 (April 2011): 1014–24. http://dx.doi.org/10.1091/mbc.e10-09-0740.
Анотація:
Axonal growth is essential for establishing neuronal circuits during brain development and for regenerative processes in the adult brain. Unfortunately, the extracellular signals controlling axonal growth are poorly understood. Here we report that a reduction in extracellular ATP levels by tissue-nonspecific alkaline phosphatase (TNAP) is essential for the development of neuritic processes by cultured hippocampal neurons. Selective blockade of TNAP activity with levamisole or specific TNAP knockdown with short hairpin RNA interference inhibited the growth and branching of principal axons, whereas addition of alkaline phosphatase (ALP) promoted axonal growth. Neither activation nor inhibition of adenosine receptors affected the axonal growth, excluding the contribution of extracellular adenosine as a potential hydrolysis product of extracellular ATP to the TNAP-mediated effects. TNAP was colocalized at axonal growth cones with ionotropic ATP receptors (P2X7 receptor), whose activation inhibited axonal growth. Additional analyses suggested a close functional interrelation of TNAP and P2X7 receptors whereby TNAP prevents P2X7 receptor activation by hydrolyzing ATP in the immediate environment of the receptor. Furthermore inhibition of P2X7 receptor reduced TNAP expression, whereas addition of ALP enhanced P2X7 receptor expression. Our results demonstrate that TNAP, regulating both ligand availability and protein expression of P2X7 receptor, is essential for axonal development.
39
Srivastava, Ojas, Chris Hanstock, Sneha Chenji, Dennell Mah, Dean Eurich, Daniel Ta, Peter Seres, et al. "Cerebral degeneration in amyotrophic lateral sclerosis." Neurology: Clinical Practice 9, no. 5 (June 5, 2019): 400–407. http://dx.doi.org/10.1212/cpj.0000000000000674.
Анотація:
BackgroundWe investigated cerebral degeneration and neurochemistry in patients with amyotrophic lateral sclerosis (ALS) using magnetic resonance spectroscopy (MRS).MethodsWe prospectively studied 65 patients and 43 age-matched healthy controls. Participants were recruited from 4 centers as part of a study in the Canadian ALS Neuroimaging Consortium. All participants underwent single-voxel proton MRS using a protocol standardized across all sites. Metabolites reflecting neuronal integrity (total N-acetyl aspartyl moieties [tNAA]) and gliosis (myo-inositol [Ino]), as well as creatine (Cr) and choline (Cho), were quantified in the midline motor cortex and midline prefrontal cortex. Comparisons were made between patients with ALS and healthy controls. Metabolites were correlated with clinical measures of upper motor neuron dysfunction, disease progression rate, and cognitive performance.ResultsIn the motor cortex, tNAA/Cr, tNAA/Cho, and tNAA/Ino ratios were reduced in the ALS group compared with controls. Group differences in tNAA/Cr and tNAA/Cho in the prefrontal cortex displayed reduced ratios in ALS patients; however, these were not statistically significant. Reduced motor cortex ratios were associated with slower foot tapping rate, whereas only motor tNAA/Ino was associated with finger tapping rate. Disease progression rate was associated with motor tNAA/Cho. Verbal fluency, semantic fluency, and digit span forwards and backwards were associated with prefrontal tNAA/Cr.ConclusionsThis study demonstrates that cerebral degeneration in ALS is more pronounced in the motor than prefrontal cortex, that multicenter MRS studies are feasible, and that motor tNAA/Ino shows promise as a potential biomarker.
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Zhang, Xueli, and Xuedong Gong. "A computational study on new oxidizers as replacements for ammonium perchlorate: tetranitroacetimidic acid and tetranitroacetamide." Canadian Journal of Chemistry 95, no. 2 (February 2017): 199–206. http://dx.doi.org/10.1139/cjc-2016-0468.
Анотація:
High energetic materials tetranitroacetimidic acid (TNAA) and tetranitroacetamide (NTNAA) with positive oxygen balance (OB = 30%) are highly potential replacements for ammonium perchlorate (AP). Tautomerization from TNAA to NTNAA is feasible, reflected by the activation energy of 160.2∼170.0 kJ/mol. No transition state appears on the C–NO2 bond breaking, which triggers pyrolysis of two compounds. The C–NO2 bond dissociation energies are 116.1∼167.2 kJ/mol and 120.4∼174.6 kJ/mol for TNAA and NTNAA, respectively. The chemical stabilities of TNAA and NTNAA are higher than that of the insensitive explosive 1,1-diamino-2,2-dinitroethylene. TNAA and NTNAA possess lower impact sensitivities (h50 ≥ 77.51 cm) than AP does. Detonation properties of the composite explosives containing TNAA or NTNAA are comparable with that of the composite explosives containing AP. The acceptable stabilities, highly positive OB, environmentally friendly decomposition products, and the comparable ability to improve detonation performance of composite explosives show that TNAA and NTNAA are potential replacements for AP as an oxidizer used in composite explosives.
41
MacGregor, G. R., B. P. Zambrowicz, and P. Soriano. "Tissue non-specific alkaline phosphatase is expressed in both embryonic and extraembryonic lineages during mouse embryogenesis but is not required for migration of primordial germ cells." Development 121, no. 5 (May 1, 1995): 1487–96. http://dx.doi.org/10.1242/dev.121.5.1487.
Анотація:
Mouse primordial germ cells express tissue non-specific alkaline phosphatase (TNAP) during development, but the widespread expression of another alkaline phosphatase gene in the early embryo limits the potential use of this marker to trace germ cells. To attempt to identify germ cells at all stages during embryonic development and to understand the role of TNAP in germ cell ontogeny, mice carrying a beta geo (lacZ/neor) disrupted allele of the TNAP gene were generated by homologous recombination in embryonic stem cells. Using beta-galactosidase activity, the embryonic pattern of TNAP expression was examined from the blastocyst stage to embryonic day 14. Results indicate that primordial germ cell progenitors do not express TNAP prior to gastrulation although at earlier times TNAP expression is found in an extraembryonic lineage destined to form the chorion. In homozygous mutants, primordial germ cells appear unaffected indicating that TNAP is not essential for their development or migration.
42
Jackson, Edwin K., Dongmei Cheng, Vladimir B. Ritov, and Zaichuan Mi. "Alkaline Phosphatase Activity Is a Key Determinant of Vascular Responsiveness to Norepinephrine." Hypertension 76, no. 4 (October 2020): 1308–18. http://dx.doi.org/10.1161/hypertensionaha.120.15822.
Анотація:
Here, we tested the hypothesis that TNAP (tissue nonspecific alkaline phosphatase) modulates vascular responsiveness to norepinephrine. In the isolated, Tyrode’s-perfused rat mesentery, 50 µmol/L of L-p-bromotetramisole (L-p-BT; selective TNAP inhibitor, K i =56 µmol/L) significantly reduced TNAP activity and caused a significant 9.0-fold rightward-shift in the norepinephrine concentration versus vasoconstriction relationship. At 100 µmol/L, L-p-BT further reduced mesenteric TNAP activity and caused an additional significant right-shift of the norepinephrine concentration versus vasoconstriction relationship. A higher concentration (200 µmol/L) of L-p-BT had no further effect on either mesenteric TNAP activity or norepinephrine-induced vasoconstriction. L-p-BT did not alter vascular responses to vasopressin, thus ruling-out nonspecific suppression of vascular reactivity. Since in the rat mesenteric vasculature α 1 -adrenoceptors mediate norepinephrine-induced vasoconstriction, these finding indicate that TNAP inhibition selectively interferes with α 1 -adrenoceptor signaling. Additional experiments showed that the effects of TNAP inhibition on norepinephrine-induced vasoconstriction were not mediated by accumulation of pyrophosphate or ATP (TNAP substrates) nor by reduced adenosine levels (TNAP product). TNAP inhibition significantly reduced the Hillslope of the norepinephrine concentration versus vasoconstriction relationship from 1.8±0.2 (consistent with positive cooperativity of α 1 -adrenoceptor signaling) to 1.0±0.1 (no cooperativity). Selective activation of A 1 -adenosine receptors, which are known to participate in coincident signaling with α 1 -adrenoceptors, reversed the suppressive effects of L-p-BT on norepinephrine-induced vasoconstriction. In vivo, L-p-BT administration achieved plasma levels of ≈60 µmol/L and inhibited mesenteric vascular responses to exogenous norepinephrine and sympathetic nerve stimulation. TNAP modulates vascular responses to norepinephrine likely by affecting positive cooperativity of α 1 -adrenoceptor signaling via a mechanism involving A 1 receptor signaling.
43
Yan, Zhao Xiong, Zhi Hua Xu, and Li Hong Zhu. "Visible-Light Illumination Enhanced Hydrogen Evolution on CuO Modified TiO2 Nanotube Arrays/Ti Electrocatalyst." Advanced Materials Research 772 (September 2013): 343–48. http://dx.doi.org/10.4028/www.scientific.net/amr.772.343.
Анотація:
TiO2nanotube arrays (TNAs) modified by CuO (CuO-TNAs) catalysts were prepared by an impregnating-calcinating method using the electrochemically prepared TNAs and Cu (NO3)2as precursors and were characterized by scanning electron microscope, transmission electron microscopy, X-ray diffraction spectroscopy and UV-visible spectroscopy. The electrocatalytic properties of the CuO-TNAs samples for hydrogen evolution reaction (HER) were investigated by linear sweep curves, electrochemical impedance spectrum and current-time curves. The results showed that the electrocatalytic activity of TNAs for hydrogen evolution reaction (HER) was significantly enhanced by CuO modification, and the electrocatalytic activity of CuO-TNAs catalysts could be further promoted by visible-light illumination. The combination of visible-light irradiation with applying a controlled potential may provide new insight into enhancing the performances of the cathode for hydrogen evolution reaction.
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VIEILLE, Claire, Harini KRISHNAMURTHY, Hyung-Hwan HYUN, Alexei SAVCHENKO, Honggao YAN, and J. Gregory ZEIKUS. "Thermotoga neapolitana adenylate kinase is highly active at 30 degreesC." Biochemical Journal 372, no. 2 (June 1, 2003): 577–85. http://dx.doi.org/10.1042/bj20021377.
Анотація:
The adenylate kinase (AK) gene from Thermotoga neapolitana, a hyperthermophilic bacterium, was cloned and overexpressed in Escherichia coli, and the recombinant enzyme was biochemically characterized. The T. neapolitana AK (TNAK) sequence indicates that this enzyme belongs to the long bacterial AKs. TNAK contains the four cysteine residues that bind Zn2+ in all Gram-positive AKs and in a few other Zn2+-containing bacterial AKs. Atomic emission spectroscopy and titration data indicate a content of 1 mol of Zn2+/mol of recombinant TNAK. The EDTA-treated enzyme has a melting temperature (Tm=93.5 °C) 6.2 °C below that of the holoenzyme (99.7 °C), identifying Zn2+ as a stabilizing feature in TNAK. TNAK is a monomeric enzyme with a molecular mass of approx. 25 kDa. TNAK displays Vmax and Km values at 30 °C identical with those of the E. coli AK at 30 °C, and displays very high activity at 80 °C, with a specific activity above 8000 units/mg. The unusually high activity of TNAK at 30 °C makes it an interesting model to test the role of enzyme flexibility in activity.
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Oudeman, Eline A., Jacoba P. Greving, Renske M. Van den Berg-Vos, Geert Jan Biessels, Esther E. Bron, Robert van Oostenbrugge, Jeroen de Bresser, and L. Jaap Kappelle. "Nonfocal Transient Neurological Attacks Are Associated With Cerebral Small Vessel Disease." Stroke 50, no. 12 (December 2019): 3540–44. http://dx.doi.org/10.1161/strokeaha.119.025328.
Анотація:
Background and Purpose— Nonfocal transient neurological attacks (TNAs), such as unsteadiness, bilateral weakness, or confusion, are associated with an increased risk of stroke and dementia. Cerebral ischemia plays a role in their pathogenesis, but the precise mechanisms are unknown. We hypothesized that cerebral small vessel disease is involved in the pathogenesis of TNAs and assessed the relation between TNAs and manifestations of cerebral small vessel disease on magnetic resonance imaging. Methods— We included participants from the HBC (Heart-Brain Connection) study. In this study, hemodynamic and cardiovascular contributions to cognitive impairment have been studied in patients with heart failure, carotid artery occlusion, or possible vascular cognitive impairment, as well as in a reference group. We excluded participants with a history of stroke or transient ischemic attacks. The occurrence of the following 8 TNAs was assessed with a standardized interview: unconsciousness, confusion, amnesia, unsteadiness, bilateral leg weakness, blurred vision, nonrotatory dizziness, and paresthesias. The occurrence of TNAs was related to the presence of lacunes or white matter hyperintensities (Fazekas score, ≥2; early confluent or confluent lesions) in logistic regression analysis, adjusted for age, sex, and hypertension. Results— Of 304 participants (60% men; mean age, 67±9 years), 63 participants (21%) experienced ≥1 TNAs. Lacunes and early confluent or confluent white matter hyperintensities were more common in participants with TNAs than in participants without TNAs (35% versus 20%; adjusted odds ratio, 2.32 [95% CI, 1.22–4.40] and 48% versus 27%; adjusted odds ratio, 2.65 [95% CI, 1.44–4.90], respectively). Conclusions— In our study, TNAs are associated with the presence of lacunes and early confluent or confluent white matter hyperintensities of presumed vascular origin, which indicates that cerebral small vessel disease might play a role in the pathogenesis of TNAs.
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Mahmud, Mahmud Ahmad Ismail, Álvaro Roberto Crespo Merlo, Irênio Gomes, Jefferson Becker, and Daniel Bocchese Nora. "Relação entre tensão neural adversa e estudos de condução nervosa em pacientes com sintomas da sídrome do túnel do carpo." Arquivos de Neuro-Psiquiatria 64, no. 2a (June 2006): 277–82. http://dx.doi.org/10.1590/s0004-282x2006000200019.
Анотація:
O propósito deste estudo foi avaliar, através de uma série de casos, a relação entre tensão neural adversa do nervo mediano (TNAm) e o parâmetro eletrofisiológico em 38 pacientes com sintomas da síndrome do túnel do carpo (STC), submetidos a estudos de condução nervosa (ECN). As principais medidas foram a TNAm obtida no teste de provocação de tensão neural (TPTN) e parâmetros dos ECN, dividindo-se os braços avaliados em três grupos: normal, com alteração eletrofisiológica sem gravidade e com alteração eletrofisiológica grave. Correlação significante entre TNAm e parâmetros dos ECN foram encontrados (p<0,05), bem como entre a TNAm e os três grupos definidos pela alteração eletrofisiológica (r s=+0.437, p=0,002). Valores de TNAm foram significantemente maiores nos braços com diagnóstico eletrofisiológico (p=0,007). Sugere-se que a TNAm tem participação na fisiopatologia da STC, indicando o uso de procedimentos terapêuticos que diminuam ou previnam a tensão neural.
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Nwafor, Divine C., Allison L. Brichacek, Ahsan Ali, and Candice M. Brown. "Tissue-Nonspecific Alkaline Phosphatase in Central Nervous System Health and Disease: A Focus on Brain Microvascular Endothelial Cells." International Journal of Molecular Sciences 22, no. 10 (May 17, 2021): 5257. http://dx.doi.org/10.3390/ijms22105257.
Анотація:
Tissue-nonspecific alkaline phosphatase (TNAP) is an ectoenzyme bound to the plasma membranes of numerous cells via a glycosylphosphatidylinositol (GPI) moiety. TNAP’s function is well-recognized from earlier studies establishing its important role in bone mineralization. TNAP is also highly expressed in cerebral microvessels; however, its function in brain cerebral microvessels is poorly understood. In recent years, few studies have begun to delineate a role for TNAP in brain microvascular endothelial cells (BMECs)—a key component of cerebral microvessels. This review summarizes important information on the role of BMEC TNAP, and its implication in health and disease. Furthermore, we discuss current models and tools that may assist researchers in elucidating the function of TNAP in BMECs.
48
Noeiaghaei, T., J. H. Yun, S. W. Nam, K. D. Zoh, V. G. Gomes, J. O. Kim, and S. R. Chae. "The influence of geometrical characteristics on the photocatalytic activity of TiO2 nanotube arrays for degradation of refractory organic pollutants in wastewater." Water Science and Technology 71, no. 9 (February 20, 2015): 1301–9. http://dx.doi.org/10.2166/wst.2015.078.
Анотація:
The effects of geometrical characteristics such as surface area (SA) and porosity of TiO2 nanotube arrays (TNAs) on its photocatalytic activity were investigated by applying variable voltages and reaction times for the anodization of Ti substrates. While larger SA of nanotubes was observed under higher applied potential, the porosity of TNAs decreased by increasing anodizing voltage. Under applied potential of 80 V, the SA of TNAs increased from 0.164 to 0.471 m2/g as anodization time increased from 1 to 5 hours, respectively. However, no significant effect on the porosity of TNAs was observed. On the other hand, both SA and porosity of TNAs, synthesized at 60 V, increased by augmenting the anodization time from 1 to 3 hours. But further increasing of anodization time to 5 hours resulted in a decreased SA of TNAs with no effect on their porosity. Accordingly, the TNAs with SA of 0.368 m2/g and porosity of 47% showed the highest photocatalytic activity for degradation of 4-chlorobenzoic acid (4CBA). Finally, the degradation of refractory model compounds such as carbamazepine and bisphenol-A was tested and more than 50% of both compounds could be degraded under UV-A irradiation (λmax = 365 nm).
49
Hashishin, Takeshi, Keisuke Misawa, Kazuo Kojima, Chihiro Yogi, and Jun Tamaki. "Photocatalytic Properties of Size-Controlled Titania Nanotube Arrays." International Journal of Electrochemistry 2011 (2011): 1–7. http://dx.doi.org/10.4061/2011/656939.
Анотація:
The titania nanotube arrays (TNAs) with smooth surface was synthesized by anodization of titanium foil with 3 cm2in square area using the electrolyte composed of 0.2 wt% NH4F and 0.5 vol% H2SO4in ethylene glycol in order to evaluate the methylene blue photodegradation under ultra-violet irradiation. The tube length and inner diameter as a size parameter were controlled by the anodization time from 5 to 10 h and applied voltage from 10 to 50 V. The titania nanotube arrays (TNAs) annealed at 300 to 500°C were assigned to anatase phase, and TNAs at 600°C had both phase of anatase and rutile. The crystallite size and the apparent rate constant were increased with the increase in the annealing temperature of TNAs from 300 to 500°C. The bigger crystallite size of TNAs is suggested to be related to the increase in the amount of hole at the valence band, leading to the decrease in the apparent rate constant of MB degradation. Interestingly, the four kinds of linear relationship with the apparent rate constant were seen in both the inner diameter of TNAs and the length. Consequently, the apparent rate constant strongly depended on inner diameter of TNAs.
50
Wang, Chao, Da Chen, Shu Liu, Xia Ni Huang, Yue Xiang Huang, and Kang Ying Shu. "Preparation of Well-Ordered TiO2 Nanotube Arrays by Electrochemical Anodization of Titanium Foil in Neutral Electrolytes." Advanced Materials Research 233-235 (May 2011): 2047–50. http://dx.doi.org/10.4028/www.scientific.net/amr.233-235.2047.
Анотація:
To obtain high performance TiO2nanotube arrays (TNAs)-based material is interesting because of its wide applications in photocatalysis field such as solar energy conversion, photocatalysis and sensors. In the present work, the well-ordered TNAs were prepared by electrochemical anodization of titanium foil in the SO42−/F−based electrolyte under 20 V for 2 h during which the Ti foil and Pt wire were used as anode and cathode, respectively. The FESEM results showed that the as-obtained TNAs were well-aligned on Ti substrate with ~ 1.5 μm in length and ~ 100 nm pore in diameter. The XRD results indicated that the as-formed TNAs was in the form of amorphous and could be transformed into crystalline anatase phase under the heat treatment at 450 °C. Meanwhile, the UV-vis diffuse reflectance spectra demonstrated that the band-gap of the obtained TNAs was narrower than the commercial TiO2nanoparticles, indicating a better photocatalytic activity of the as-prepared TNAs over the commercial TiO2nanoparticles.