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31.
Planktonic heterotrophic bacteria in lakes utilize the labile fraction of dissolved organic carbon (DOC), although information
about seasonal changes in labile DOC in hypertrophic lakes in terms of absolute amount and relative proportion of the total
DOC is still limited. We conducted DOC decomposition experiments using GF/F filtrates in water samples from hypertrophic Furuike
Pond, together with monitoring of DOC concentration and bacterial abundance in water samples from the pond, to examine seasonal
changes in the amount of labile DOC and growth of bacteria on labile DOC. DOC concentrations fluctuated between 2.7 and 11
mg C l−1, and bacterial abundance fluctuated between 1.5 × 106 and 1.0 × 108 cells ml−1. In the DOC decomposition experiment when grazers of bacteria were removed, small portions of DOC (18% ± 12%) were labile
for decomposition by bacteria, and the growth yield of bacteria on labile DOC ranged between 3.3% and 19%. Furthermore, addition
of nitrogen to water samples enhanced bacterial growth. Thus, not only labile DOC but also nitrogen limited bacterial growth
in the pond. Considering the results in the present study together with those of previous studies, bacterial abundance in
Furuike Pond is subjected to bottom-up control, such as by limitation of DOC and nitrogen throughout the year, although top-down
control of bacterial abundance such as by grazing is seasonally important.
Received: May 1, 2001 / Accepted: July 22, 2001 相似文献
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33.
S Nishibe M Ogawa A Murata K Nakamura T Hatanaka J Kambayashi G Kosaki 《Life sciences》1983,32(14):1613-1620
Acetylcholine and arachidonic acid induced catecholamine secretion from isolated bovine adrenal medullary cells. Protease inhibitors and calmodulin inhibitors inhibited catecholamine secretion induced by acetylcholine but did not inhibit the secretion induced by arachidonic acid. BW 755-C, a lipoxygenase inhibitor, inhibited catecholamine release induced by acetylcholine. These results suggest that a protease and calmodulin are involved in the successive reaction after stimulus-receptor coupling and arachidonic acid or its metabolites might be important in catecholamine secretion from bovine adrenal medullary cells. 相似文献
34.
Maksut Coşkun Akiyo Sakushima Sansei Nishibe Sueo Hisada Nevin Tanker 《Phytochemistry》1982,21(6):1453-1454
A new phloroglucinol derivative, abbreviatin BB, has been isolated from Dryopteris abbreviata. Its structure was elucidated to be methylene-bis-met 相似文献
35.
M I Wahl G A Jones S Nishibe S G Rhee G Carpenter 《The Journal of biological chemistry》1992,267(15):10447-10456
We demonstrated previously tyrosine phosphorylation-dependent modulation of phospholipase C-gamma 1 (PLC-gamma 1) catalytic activity (Nishibe, S., Wahl, M. I., Hernandez-Sotomayor, S. M. T., Tonks, N. K., Rhee, S. G., and Carpenter, G. (1990) Science 250, 1253-1256). The increase in PLC-gamma 1 catalytic activity in A-431 cells occurs rapidly, with maximal activation 5 min after epidermal growth factor (EGF) stimulation. Certain other growth factors (fibroblast growth factor, platelet-derived growth factor) also stimulate PLC-gamma 1 catalytic activity, whereas insulin does not. A similar increase in PLC-gamma 1 specific activity (2-3-fold) was observed in both soluble (cytosol) and particulate (membrane) preparations from EGF-treated cells. Tyrosine-phosphorylated PLC-gamma 1 was detected in both cytosol and membrane fractions in lysates from EGF-treated A-431 cells, but the proportion of tyrosine-phosphorylated PLC-gamma 1 was higher in the cytosol (approximately 50%) than in the membrane (approximately 20%). Because a micellar concentration of the non-ionic detergent Triton X-100 allows detection of the tyrosine phosphorylation-dependent increase in PLC-gamma 1 catalytic activity in this assay, we evaluated the kinetic properties of PLC-gamma 1, immunoprecipitated from cytosol of control or EGF-treated cells, using substrate, phosphatidylinositol 4,5-bisphosphate (PtdIns 4,5-P2), solubilized in Triton X-100 at various molar ratios. The behavior of the control enzyme differed from the EGF-activated enzyme with respect to both Ks and Km. The control enzyme has a 7.5-fold higher Ks value than the activated enzyme (1.5 mM as compared with 0.22 mM). Activation by EGF is also a positive allosteric modifier of PLC-gamma 1-catalyzed PtdIns 4,5-P2 hydrolysis, i.e. the activated enzyme displayed apparent Michalis-Menton kinetics, with a Km of 0.6 mol fraction PtdIns 4,5-P2, whereas the control enzyme displayed sigmoidal kinetics with respect to PtdIns 4,5-P2 hydrolysis. At low substrate mol fractions (e.g. 0.07), the reaction velocity of the control enzyme was 4-fold lower than the activated enzyme. However, at a high substrate mol fraction (e.g. 0.33), the estimated maximal reaction velocities (Vmax) for both forms of PLC-gamma 1 were equivalent. PLC-gamma 1 activity from both control and EGF-treated cells was stimulated by increasing nanomolar Ca2+ concentrations. Although the catalytic activity of PLC-gamma 1 from EGF-treated cells was greater than control PLC-gamma 1 at every Ca2+ concentration tested, the relative stimulation of activity was markedly greater at Ca2+ concentrations above approximately 300 nM. 相似文献
36.
Hiroki Tsukamoto Sueo Hisada Sansei Nishibe David G. Roux John P. Rourke 《Phytochemistry》1984,23(3):699-700
Esculetin and scopoletin were isolated from the bark of Olea africana while isoscopoletin and scoparone were isolated from the bark of Olea capensis. The distribution of these coumarins in Olea species from South Africa is described. 相似文献
37.
Nishibe A Kijima Y Fukunaga M Nishiwaki N Sakai T Nakagawa Y Hata T 《Prostaglandins, leukotrienes, and essential fatty acids》2008,78(4-5):257-263
8-Iso-prostaglandin F(2)(alpha) (8-iso-PGF(2)(alpha)), a representative isoprostane, is a reliable biomarker for enhanced oxidant stress in vivo. Its urinary excretion has been proposed as a risk marker in patients with coronary heart disease. Isoprostane content has not yet been well elucidated so far in human coronary plaques. The aim of this study was to evaluate content of immunoreactive 8-iso-PGF(2)(alpha) in directional coronary atherectomy (DCA) specimens from patients with coronary heart diseases. Twenty-seven patients with stable angina pectoris (SAP) and 8 vulnerable patients (5 patients with unstable angina pectoris and 3 with recent myocardial infarction) were subjected to DCA. The specimens from SAP consisted of 14 de novo and 13 restenotic lesions, whereas those from the vulnerable patients were all de novo lesions. Total 8-iso-PGF(2)(alpha) content in the DCA specimens from the vulnerable patients was significantly greater than that from patients with SAP (5.48 (2.70-10.43) versus 2.38 (1.19-4.32)ng/g tissue, median (interquartile range), P<0.05). There was no significant difference in total 8-iso-PGF(2)(alpha) content between de novo and restenotic lesions from patients with SAP (3.25 (1.48-5.05) versus 1.57 (0.62-2.47)ng/g tissue, respectively, P=0.895). Total 8-iso-PGF(2)(alpha) content in apparently normal peripheral artery specimens was only 0.34 (0.26-0.46)ng/g tissue. In conclusion, 8-iso-PGF(2)(alpha) was enriched in the DCA specimens from vulnerable patients, suggesting a crucial role of free radicals in formation of vulnerable plaques and a putative benefit of anti-oxidant therapy on these patients. 相似文献
38.
S Sardari Y Mori K Horita R G Micetich S Nishibe M Daneshtalab 《Bioorganic & medicinal chemistry》1999,7(9):1933-1940
Angelicin, a naturally occurring furanocoumarin, that showed antifungal activity, was considered as a lead structure for a group of synthetic coumarins. Antifungal activities of the synthesized coumarins and angelicin derivatives were reported against Candida albicans, Cryptococcus neoformans, Saccharomyces cerevisiae and Aspergillus niger. Human cell line cytotoxicity of several coumarins was evaluated against KB cells. Angelicin and several potent antifungals showed to be non-toxic in this assay. 相似文献
39.
Glutamate decarboxylase (GAD) catalyzes the synthesis of gamma-aminobutyric acid (GABA), an inhibitory neurotransmitter, from glutamate. An expression of GAD protein has been reported for brain and pancreas, but not for skin. In this study, we present evidence that GAD67 mRNA and protein are expressed in mouse skin and in human dermal fibroblasts. The expression of GAD67 gene is weaker in aged mouse than the young one. To further explore the function of GAD in skin, we have examined a potential role(s) of GABA in human dermal fibroblasts. We have observed that GABA stimulates the synthesis of hyaluronic acid (HA) and enhances the survival rate of the dermal fibroblasts when fibroblasts are exposed to H(2)O(2) an oxidative stress agent. Also observed were lowering the levels of HA and collagen in the embryonic skin from GAD67 deficient mouse as compared to those from the wild-type (WT) mouse. In this study, we have presented the evidences that GAD67 is localized in the dermis and is potentially involved in variety of skin activities. 相似文献
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