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排序方式: 共有806条查询结果,搜索用时 15 毫秒
71.
Tetrahydrobiopterin (BH(4)) is an essential cofactor for the nitric oxide (NO) synthases and the aromatic amino acid hydroxylases. Insufficient BH(4) has been implicated in various cardiovascular and neurological disorders. GTP cyclohydrolase 1 (GTPCH-1) is the rate-limiting enzyme for de novo biosynthesis of BH(4). The authors have recently shown that the interaction of GTPCH-1 with GTP cyclohydrolase feedback regulatory protein (GFRP) inhibits endothelial GTPCH-1 enzyme activity, BH(4) levels, and NO production. They propose that agents that disrupt the GTPCH-1/GFRP interaction can increase cellular GTPCH-1 activity, BH(4) levels, and NO production. They developed and optimized a novel time-resolved fluorescence resonance energy transfer (TR-FRET) assay to monitor the interaction of GTPCH-1 and GFRP. This assay is highly sensitive and stable and has a signal-to-background ratio (S/B) greater than 12 and a Z' factor greater than 0.8. This assay was used in an ultra-high-throughput screening (uHTS) format to screen the Library of Pharmacologically Active Compounds. Using independent protein-protein interaction and cellular activity assays, the authors identified compounds that disrupt GTPCH-1/GFRP binding and increase endothelial cell biopterin levels. Thus, this TR-FRET assay could be applied in future uHTS of additional libraries to search for molecules that increase GTPCH-1 activity and BH(4) levels. 相似文献
72.
Liang Zhang Zhongyang Ding Peng Xu Yuhong Wang Zhenghua Gu Zhu Qian Guiyang Shi Kechang Zhang 《Biotechnology and Bioprocess Engineering》2011,16(3):457-461
Tyrosinase is a key enzyme in the biosynthesis of melanin, and the use of inhibitors against tyrosinase can prevent hyperpigmentation
by inhibiting enzymatic oxidation. However, the current use of tyrosine inhibitors is limited by their low activities and
high toxicities. The aim of the present research was to develop novel whitening agents, or tyrosinase-targeted medicine, from
a submerged culture of the fungus Ganoderma lucidum. Methyl lucidenate F was isolated from the ethanol-soluble-acidic components (ESACs) of G. lucidum, with the structure of ESACs elucidated via UV, LC-MS, and 13C-NMR spectral analysis. The tyrosinase inhibitory activity was measured using catechol as a substrate. Methyl lucidenate
F displayed uncompetitive inhibition of the potato tyrosinase activity, for which Lineweaver-Burk plots revealed a maximum
reaction rate (V
max) of 0.4367/min, Michaelis constant (K
m) of 6.765 mM and uncompetitive inhibition constant (K
i) of 19.22 μM. Meanwhile, methyl lucidenate F (tetra cyclic triterpenoid) exhibited high tyrosinase inhibitory activity, with
an IC50 of 32.23 μM. These results suggest that methyl lucidenate F may serve as a potential candidate for skin-whitening agents. 相似文献
73.
A genome-wide association study confirms previously reported loci for type 2 diabetes in Han Chinese
Cui B Zhu X Xu M Guo T Zhu D Chen G Li X Xu L Bi Y Chen Y Xu Y Li X Wang W Wang H Huang W Ning G 《PloS one》2011,6(7):e22353
Background
Genome-wide association study (GWAS) has identified more than 30 loci associated with type 2 diabetes (T2D) in Caucasians. However, genomic understanding of T2D in Asians, especially Han Chinese, is still limited.Methods and Principal Findings
A two-stage GWAS was performed in Han Chinese from Mainland China. The discovery stage included 793 T2D cases and 806 healthy controls genotyped using Illumina Human 660- and 610-Quad BeadChips; and the replication stage included two independent case-control populations (a total of 4445 T2D cases and 4458 controls) genotyped using TaqMan assay. We validated the associations of KCNQ1 (rs163182, p = 2.085×10−17, OR 1.28) and C2CD4A/B (rs1370176, p = 3.677×10−4, OR 1.124; rs1436953, p = 7.753×10−6, OR 1.141; rs7172432, p = 4.001×10−5, OR 1.134) in Han Chinese.Conclusions and Significance
Our study represents the first GWAS of T2D with both discovery and replication sample sets recruited from Han Chinese men and women residing in Mainland China. We confirmed the associations of KCNQ1 and C2CD4A/B with T2D, with the latter for the first time being examined in Han Chinese. Arguably, eight more independent loci were replicated in our GWAS. 相似文献74.
75.
76.
According to the raft hypothesis, sphingolipid-cholesterol (CHOL) microdomains are involved in numerous cellular functions. Here, we have prepared liposomes to simulate the lipid composition of rafts/caveolae using phosphatidylchone, sphingomyelin (SPM)-CHOL in vitro. Experiments of both 1,6-diphenyl-1,3,5-hexatriene and merocyanine-540 fluorescence showed that a phase transition from l(d) to l(o) can be observed clearly. In particular, we investigated the behavior of a membrane protein, plasma membrane Ca(2+)-ATPase (PMCA), in lipid rafts (l(o) phase). Three complementary approaches to characterize the physical appearance of PMCA were employed in the present study. Tryptophan intrinsic fluorescence increase, fluorescence quenching by both acrylamid and hypocrellin B decrease, and MIANS fluorescence decrease, indicate that the conformation of PMCA embedded in lipid l(o) phase is more compact than in lipid l(d) phase. Also, our results showed that PMCA activity decreased with the increase of SPM-CHOL content, in other words, with the increase of l(o) phase. This suggests that the specific domains containing high SPM-CHOL concentration are not a favorable place for PMCA activity. Finally, a possible explanation about PMCA molecules concentrated in caveolae/rafts was discussed. 相似文献
77.
Deshmukh R Zeng Y Furci LM Huang HW Morgan BN Sander S Alontaga AY Bunce RA Moënne-Loccoz P Rivera M Wilks A 《Biochemistry》2005,44(42):13713-13723
Heme oxygenases from the bacterial pathogens Neisseriae meningitidis (nm-HO) and Pseudomonas aeruginosa (pa-HO) share significant sequence identity (37%). In nm-HO, biliverdin IXalpha is the sole product of the reaction, whereas pa-HO yields predominantly biliverdin IXdelta. We have previously shown by NMR that the in-plane conformation of the heme in pa-HO is significantly different from that of nm-HO as a result of distinct interactions of the heme propionates with the protein scaffold [Caignan, G. A., Deshmukh, R., Wilks, A., Zeng, Y., Huang, H. W., Moenne-Loccoz, P., Bunce, R. A., Eastman, M. A., and Rivera, M. (2002) J. Am. Chem. Soc. 124, 14879-14892]. In the report presented here, we have extended these studies to investigate the role of the distal helix by preparing a chimera of nm-HO (nm-HOch), in which distal helix residues 107-142 of nm-HO have been replaced with the corresponding residues of the delta-regioselective pa-HO (112-147). Electronic absorption spectra, resonance Raman and FTIR spectroscopic studies confirm that the orientation and hydrogen bonding properties of the proximal His ligand are not significantly altered in the chimera relative those of the wild-type proteins. The catalytic turnover of the nm-HOch-heme complex yields almost exclusively alpha-biliverdin and a small but reproducible amount of delta-biliverdin. NMR spectroscopic studies reveal that the altered regioselectivity in the chimeric protein likely stems from a dynamic equilibrium between two alternate in-plane conformations of the heme (in-plane heme disorder). Replacement of K16 with Ala and Met31 with Lys in the chimeric protein in an effort to tune key polypeptide-heme propionate contacts largely stabilizes the in-plane conformer conducive to delta-meso hydroxylation. 相似文献
78.
Wegele R Tasler R Zeng Y Rivera M Frankenberg-Dinkel N 《The Journal of biological chemistry》2004,279(44):45791-45802
For many pathogenic bacteria like Pseudomonas aeruginosa heme is an essential source of iron. After uptake, the heme molecule is degraded by heme oxygenases to yield iron, carbon monoxide, and biliverdin. The heme oxygenase PigA is only induced under iron-limiting conditions and produces the unusual biliverdin isomers IXbeta and IXdelta. The gene for a second putative heme oxygenase in P. aeruginosa, bphO, occurs in an operon with the gene bphP encoding a bacterial phytochrome. Here we provide biochemical evidence that bphO encodes for a second heme oxygenase in P. aeruginosa. HPLC, (1)H, and (13)C NMR studies indicate that BphO is a "classic" heme oxygenase in that it produces biliverdin IXalpha. The data also suggest that the overall fold of BphO is likely to be the same as that reported for other alpha-hydroxylating heme oxygenases. Recombinant BphO was shown to prefer ferredoxins or ascorbate as a source of reducing equivalents in vitro and the rate-limiting step for the oxidation of heme to biliverdin is the release of product. In eukaryotes, the release of biliverdin is driven by biliverdin reductase, the subsequent enzyme in heme catabolism. Because P. aeruginosa lacks a biliverdin reductase homologue, data are presented indicating an involvement of the bacterial phytochrome BphP in biliverdin release from BphO and possibly from PigA. 相似文献
79.
β-1,4-galactosyltransferase-I (β-1,4-GalT-I) has two isoforms that differ only in the length of their cytoplasmic domains. In this study, we found that both the long and short isoforms of β-1,4-GalT-I were expressed in human CD4+ T lymphocytes, and localized in the cytoplasm and on the plasma membrane. The expression level of β-1,4-GalT-I was increased in CD4+ T cells after stimulation with interleukin (IL)-2, and was further increased after stimulation with IL-2 + IL-12, but decreased after stimulation with IL-2 + IL-4 when compared to stimulation with IL-2 alone. We also demonstrated that the cellular adhesion of CD4+ T cells was significantly increased upon cytokine stimulation, and was inhibited by α-lactalbumin, indicating that the increase in adhesion was positively correlated with the expression and activity of long β-1,4-GalT-I. Collectively, the data suggest that β-1,4-GalT-I plays a role in the cellular adhesion of CD4+ T cells. 相似文献
80.