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排序方式: 共有136条查询结果,搜索用时 31 毫秒
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Radchenko MV Tanaka K Waditee R Oshimi S Matsuzaki Y Fukuhara M Kobayashi H Takabe T Nakamura T 《The Journal of biological chemistry》2006,281(29):19822-19829
The intracellular level of potassium (K(+)) in Escherichia coli is regulated through multiple K(+) transport systems. Recent data indicate that not all K(+) extrusion system(s) have been identified (15). Here we report that the E. coli Na(+) (Ca(2+))/H(+) antiporter ChaA functions as a K(+) extrusion system. Cells expressing ChaA mediated K(+) efflux against a K(+) concentration gradient. E. coli strains lacking the chaA gene were unable to extrude K(+) under conditions in which wild-type cells extruded K(+). The K(+)/H(+) antiporter activity of ChaA was detected by using inverted membrane vesicles produced using a French press. Physiological growth studies indicated that E. coli uses ChaA to discard excessive K(+), which is toxic for these cells. These results suggest that ChaA K(+)/H(+) antiporter activity enables E. coli to adapt to K(+) salinity stress and to maintain K(+) homeostasis. 相似文献
23.
Yamazaki K Suzuki M Itoh T Yamamoto K Kanemitsu M Matsumura C Nakano T Sakaki T Fukami Y Imaishi H Inui H 《Journal of biochemistry》2011,149(4):487-494
Coplanar polychlorinated biphenyls included in dioxin-like compounds are bio-accumulated and adversely affect wildlife and human health. Although many researchers have studied the metabolism of PCBs, there have been few reports of the in vitro metabolism of 3,3',4,4',5-pentachlorobiphenyl (PCB126), despite the fact that it has the highest toxicity among PCB congeners. Cytochrome P450 (CYP) 1A1 proteins can metabolize some dioxins and PCBs by hydroxylation, but the activities of human and rat CYP1A1 proteins are very different. The mechanism remains unclear. From our results, rat CYP1A1 metabolized PCB126 into 4-OH-3,3',4',5-tetrachlorobiphenyl and 4-OH-3,3',4',5,5'-pentachlorobiphenyl, but human CYP1A1 did not metabolize. Homology models of the two CYP proteins, and docking studies, showed that differences in the amino acid residues forming their substrate-binding cavities led to differences in the size and shape of the cavities; only the cavity of rat CYP1A1 allowed PCB126 close enough to the haem to be metabolized. Comparison of the amino acid residues of other mammalian CYP1A1 proteins suggested that rats have a unique metabolism of xenobiotics. Our results suggest that it is necessary to be careful in human extrapolation of toxicity data estimated by using the rat as an experimental animal, especially in the case of compounds metabolized by CYP1A1. 相似文献
24.
Tsuboi S Sutoh M Hatakeyama S Hiraoka N Habuchi T Horikawa Y Hashimoto Y Yoneyama T Mori K Koie T Nakamura T Saitoh H Yamaya K Funyu T Fukuda M Ohyama C 《The EMBO journal》2011,30(15):3173-3185
The O-glycan branching enzyme, core2 β-1,6-N-acetylglucosaminyltransferase (C2GnT), forms O-glycans containing an N-acetylglucosamine branch connected to N-acetylgalactosamine (core2 O-glycans) on cell-surface glycoproteins. Here, we report that upregulation of C2GnT is closely correlated with progression of bladder tumours and that C2GnT-expressing bladder tumours use a novel strategy to increase their metastatic potential. Our results showed that C2GnT-expressing bladder tumour cells are highly metastatic due to their high ability to evade NK cell immunity and revealed the molecular mechanism of the immune evasion by C2GnT expression. Engagement of an NK-activating receptor, NKG2D, by its tumour-associated ligand, Major histocompatibility complex class I-related chain A (MICA), is critical to tumour rejection by NK cells. In C2GnT-expressing bladder tumour cells, poly-N-acetyllactosamine was present on core2 O-glycans on MICA, and galectin-3 bound the NKG2D-binding site of MICA through this poly-N-acetyllactosamine. Galectin-3 reduced the affinity of MICA for NKG2D, thereby severely impairing NK cell activation and silencing the NK cells. This new mode of NK cell silencing promotes immune evasion of C2GnT-expressing bladder tumour cells, resulting in tumour metastasis. 相似文献
25.
Rika Kuwahara Shinichiro Kawaguchi Yumi Kohara Takeshi Jojima Kimihiro Yamashita 《Cellular and molecular neurobiology》2014,34(3):333-342
Bisphenol A (BPA) is an estrogenic endocrine disruptor used for producing polycarbonate plastics and epoxy resins. This study investigated the effects of oral BPA administration on memory performance, general activity, and emotionality in adult male Sprague Dawley rats using a battery of behavioral tests, including an appetite-motivated maze test (MAZE test) used to assess spatial memory performance. In addition, in order to confirm the effects of BPA on spatial memory performance, we examined whether intrahippocampal injection of BPA affects spatial memory consolidation. In the MAZE test, although oral BPA administration at 10 mg/kg significantly altered the number of entries into the incorrect area compared to those of vehicle-treated rats, male rats given BPA through either oral administration or intrahippocampal injection failed to show significant differences in latencies to reach the reward. Also, oral BPA administration did not affect fear-motivated memory performance in the step-through passive avoidance test. Oral BPA administration at 0.05 mg/kg, the lowest dose used in this study, was correlated with a decrease in locomotor activity in the open-field test, whereas oral administration at 10 mg/kg, the highest dose used in this study, was correlated with a light anxiolytic effect in the elevated plus-maze test. The present study suggests that BPA in adulthood has little effect on spatial memory performance in male rats. 相似文献
26.
27.
Shigeki Shibata Masami Niwa Akihiko Himeno Nanette G. Gana Kazuto Shigematsu Masanori Matsumoto Kimihiro Yamashita Kohji Sumikawa Kohtaro Taniyama 《Cellular and molecular neurobiology》1997,17(1):151-156
1. The receptor autoradiographic method done on the rat lower brain stem and cerebellum plus 125I-endothelin-1, BQ-123, an antagonist for the endothelin ETA receptor, and sarafotoxin S6c, an agonist for the ETB receptor, revealed minute amounts of the ETA receptor coexisting with the ETB receptor in the caudal solitary tract nucleus of the rat lower brain stem.2. The ETB receptor is present predominantly in other parts of the lower brain stem.3. Knowledge of the heterogeneous distribution of the central endothelin receptor subtypes aids in understanding the neurophysiology of endothelins. 相似文献
28.
A rapid procedure is described for the separation of CMP-sialic acid:lactosylceramide sialyltransferase reaction components using Sep Pak C18 cartridges. The quantitative separation of the more polar nucleotide sugar, CMP-sialic acid, and its free acid from the less polar GM3-ganglioside is simple and rapid relative to previously described methods. Recovery of GM3 is optimized by the addition of phosphatidylcholine to the reaction mixture prior to the chromatographic step. Using rat liver Golgi membranes as a source of CMP-sialic acid: lactosylceramide sialyltransferase activity (GM3 synthase; ST-1), the transfer of [14C] sialic acid from CMP-[14C] sialic acid to lactosylceramide can be quantified by this assay. The procedure is reliable and may be applicable to the isolation of ganglioside products in otherin vitro glycosyltransferase assays.Abbreviations GM3
GM3-ganglioside
- II3NeuAc-LacCer
NeuAc2-3Gal1-4Glc1-1Cer
- GD1a
GD1a-ganglioside, IV3NeuAc, II3NeuAc-GgOse4Cer, NeuAc2-3Gal1-3GalNac1-4(NeuAc2-3)Gal1-4Glc1-1Cer
- GD3
GD3-ganglioside, II3(NeuAc)2LacCer, NeuAc2-8NeuAc2-3Gal1-4Glc1-1Cer
- GgOse4Cer
asialo-GM1 Gal1-3GalNAc1-4Gal1-4Glc1-1Cer
- FucGMI
fucosyl-GMI-ganglioside, Fuc1-2Gal1-3GalNAc1-4Gal1-4 Glc1-1Cer
- ST-1
GM3 synthase, CMP-sialic acid:lactosylceramide sialyltransferase
- LacCer
lactosylceramide, Gal1-4Glc1-1Cer
- CMP-NeuAc
cytidine 5-monophospho-N-acetylneuraminic acid
- PC
phosphatidylcholine
- PMSF
phenylmethylsulfonyl fluoride 相似文献
29.
The inhibitory effects of immunosuppressive factors, dexamethasone and interleukin-4, on NF-kappaB-mediated protease production by oral cancer. 总被引:3,自引:0,他引:3
Matrix metalloproteinase-9 (MMP-9) produced by tumor cells is known to be implicated in the invasion of squamous cell carcinoma (SCC). In the process of searching for agents to inhibit MMP-9 in cancer, immunosuppressive factors, dexamethasone (DEX) and interleukin-4 (IL-4) were found to inhibit protein production as well as gene expression of MMP-9 in tumor necrosis factor alpha (TNFalpha)-stimulated SCC cells. DEX and IL-4 could also suppress the expression of urokinase type plasminogen activator (uPA) to prevent the conversion from the proenzyme form of MMP-9 to its active form. Regarding their mechanisms to inhibit the expression of MMP-9 and uPA, DEX and IL-4 had no effect on the cell surface levels of TNFalpha receptors, but inhibited the activation of NF-kappaB and NF-kappaB-dependent gene expression. DEX, but not IL-4, could strongly augment the TNFalpha-induced expression of IkappaBalpha in SCC cells. These results suggest that DEX and IL-4 suppress not only immunological reactions, but also tumor invasion by targeting NF-kappaB. 相似文献
30.
DEAD-box RNA helicase subunits of the Drosha complex are required for processing of rRNA and a subset of microRNAs 总被引:5,自引:0,他引:5
Fukuda T Yamagata K Fujiyama S Matsumoto T Koshida I Yoshimura K Mihara M Naitou M Endoh H Nakamura T Akimoto C Yamamoto Y Katagiri T Foulds C Takezawa S Kitagawa H Takeyama K O'Malley BW Kato S 《Nature cell biology》2007,9(5):604-611
MicroRNAs (miRNAs) control cell proliferation, differentiation and fate through modulation of gene expression by partially base-pairing with target mRNA sequences. Drosha is an RNase III enzyme that is the catalytic subunit of a large complex that cleaves pri-miRNAs with distinct structures into pre-miRNAs. Here, we show that both the p68 and p72 DEAD-box RNA helicase subunits in the mouse Drosha complex are indispensable for survival in mice, and both are required for primary miRNA and rRNA processing. Gene disruption of either p68 or p72 in mice resulted in early lethality, and in both p68(-/-) and p72(-/-) embryos, expression levels of a set of, but not all, miRNAs and 5.8S rRNA were significantly lowered. In p72(-/-) MEF cells, expression of p72, but not a mutant lacking ATPase activity, restored the impaired expression of miRNAs and 5.8S rRNA. Furthermore, we purified the large complex of mouse Drosha and showed it could generate pre-miRNA and 5.8S rRNA in vitro. Thus, we suggest that DEAD-box RNA helicase subunits are required for recognition of a subset of primary miRNAs in mDrosha-mediated processing. 相似文献