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排序方式: 共有1023条查询结果,搜索用时 15 毫秒
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N E Houtia J C Mazière C Mazière M Auclair L Mora J Gardette J Polonovski 《Biochemical and biophysical research communications》1987,142(1):120-127
The effect of dibutyryl-cyclic AMP (dbcAMP) and theophylline was investigated on oleic acid incorporation into cholesteryl esters and triacylglycerols in the mouse monocyte-macrophage cell line J 774. 24h pretreatment of macrophages with dbcAMP decreased cholesteryl ester formation in a dose-dependent manner (about 4 fold reduction for dbcAMP 10(-4)M + theophylline 10(-3)M), while oleic acid incorporation into triacylglycerols was markedly (2 to 3 fold) enhanced. The catabolism of acetylated LDL was only slightly affected (about 15-20% reduction with dbcAMP 5 X 10(-4)M + theophylline 10(-3)M). Acyl Coenzyme A: cholesterol-O-acyl-transferase activity, measured in vitro on cell homogenates, was reduced in dbcAMP-treated cells, whereas diacylglycerol acyltransferase activity was increased. These results suggest that cyclic AMP can modulate cholesteryl ester and triacylglycerol formation in macrophages, and that these metabolisms are inversely regulated. Agents which increase cyclic AMP intracellular level could be of interest for reducing cholesteryl ester accumulation in macrophages. 相似文献
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Introduction of the Escherichia coli gdhA gene into Rhizobium phaseoli: effect on nitrogen fixation. 总被引:1,自引:1,他引:0 下载免费PDF全文
Rhizobium phaseoli lacks glutamate dehydrogenase (GDH) and assimilates ammonium by the glutamine synthetase-glutamate synthase pathway. A strain of R. phaseoli harboring the Escherichia coli GDH structural gene (gdhA) was constructed. GDH activity was expressed in R. phaseoli in the free-living state and in symbiosis. Nodules with bacteroids that expressed GDH activity had severe impairment of nitrogen fixation. Also, R. phaseoli cells that lost GDH activity and assimilated ammonium by the glutamine synthetase-glutamate synthase pathway preferentially nodulated Phaseolus vulgaris. 相似文献
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Ammonium assimilation in Rhizobium phaseoli by the glutamine synthetase-glutamate synthase pathway. 总被引:8,自引:7,他引:1 下载免费PDF全文
Evidence from in vitro and in vivo studies showed that in Rhizobium phaseoli ammonium is assimilated by the glutamine synthetase (GS)-glutamate synthase NADPH pathway. No glutamate dehydrogenase activity was detected. R. phaseoli has two GS enzymes, as do other rhizobia. The two GS activities are regulated on the basis of the requirement for low (GSI) or high (GSII) ammonium assimilation. When the 2-oxoglutarate/glutamine ratio decreases, GSI is adenylylated. When GSI is inactivated, GSII is induced. However, induction of GSII activity varied depending on the rate of change of this ratio. GSII was inactivated after the addition of high ammonium concentrations, when the 2-oxoglutarate/glutamine ratio decreased rapidly. Ammonium inactivation resulted in alteration of the catalytic and physical properties of GSII. GSII inactivation was not relieved by shifting of the cultures to glutamate. After GSII inactivation, ammonium was excreted into the medium. Glutamate synthase activity was inhibited by some organic acids and repressed when cells were grown with glutamate as the nitrogen source. 相似文献
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Nitrogen Source Regulates Glutamate Dehydrogenase NADP Synthesis in Neurospora crassa 总被引:8,自引:4,他引:4 下载免费PDF全文
Georgina Hernndez Ray Snchez-Pescador Rafael Palacios Jaime Mora 《Journal of bacteriology》1983,154(1):524-528
Neurospora crassa glutamate dehydrogenase-NADP (EC 1.3.1.3) has a higher activity when mycelium is grown on ammonium or nitrate as nitrogen source than when grown on glutamate or glutamine. Quantitative immunoelectrophoresis established that, under all conditions, enzyme activity corresponded to enzyme concentration. Isotope incorporation studies demonstrated that the nitrogen source exerts its regulation at the level of de novo enzyme synthesis. 相似文献
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A.S.C. Wan T.L. Ngiam S.L. Leung M.L. Go P.W.S. Heng P.N. Natarajan A. Shafiee M. Vossoghi F. Savabi C.G. Francisco R. Freire R. Hernandez J.A. Salazar E. Suarez G.A.Garcia De La Mora Y.Grillasca R. O. Jimeno 《Steroids》1983,41(3):309-320
The synthesis of esters of norethisterone (17α-ethynyl-17β-hydroxy-estr-4-en-3-one) with acids containing a benzene ring is described, two methods of esterification being compared in terms of yield and convenience. The activities of these esters as long-acting contraceptive agents have been evaluated. 相似文献
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C G Francisco R Freire R Hernandez J A Salazar E Suarez G A García de la Mora J A Noguez A Acosta O Jimeno 《Steroids》1983,41(3):267-275
The synthesis of nine new esters of norethisterone (17 alpha-ethynyl-17 beta-hydroxyestr-4-en-3-one) is described, with the esterifying acids bearing an acetylenic or olefinic function in a chain of eight or nine carbon atoms, for evaluation as long-acting contraceptive agents. 相似文献
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1. Carbamoyl phosphate synthetase, ornithine transcarbamoylase, the arginine-synthetase system and arginase were measured in the livers of ammoniotelic, ureotelic and uricotelic animals. The chelonian reptiles, whose nitrogen excretory patterns vary according to the habitat, and the Mexican axolotl, a neotenic species, were also studied. 2. The levels of the activities of the first three enzymes mentioned correlate with the amount of nitrogen excreted as urea. 3. The terrestrial turtle, which excretes mainly uric acid, maintains a high arginase activity but has very low levels of the activities of the other three enzymes. 4. The first three enzymes of the urea cycle vary in the phylogenic scale in a co-ordinated manner, which suggests that they are under the same regulatory mechanism. 5. Urea formation from endogenous arginine in vitro has a low efficiency in the Mexican axolotl. 6. The induction of metamorphosis in the Mexican axolotl by the administration of l-tri-iodothyronine, which causes a shift from ammonio-ureotelism to complete ureotelism, is accompanied by an increase mainly in carbamoyl phosphate synthetase and also by an improvement in the efficiency of hydrolysis of endogenous arginine in vitro to give urea. 7. The results obtained by differential centrifugation of the urea-cycle enzymes in rat and Mexican-axolotl livers are presented. The location requirements for the integration of a metabolic cycle are discussed. 相似文献