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811.
812.
Calcium control of glycogen synthase activities in mouse diaphragms, rat adipocytes and rat hepatocytes 总被引:1,自引:0,他引:1
The following article provides evidence that cellular calcium controls the activity of glycogen synthase in all three major glycogen storage tissues; muscle, fat, and liver. Depletion of cellular calcium resulted in a moderate increase of glycogen synthase %I activities in intact mouse diaphragms, in isolated rat adipocytes, and in rat hepatocytes. The increase in %I activity of glycogen synthase was more pronounced when the uridine di-phosphoglucose concentration in the glycogen synthase assay was lowered from 4.4 mM to 0.2 mM. Calcium depletion resulted in an approximately two-fold decrease in the Ka values for glucose-6-phosphate in all three tissues. The activities of glycogen synthase also correlated well with the content of cell-associated calcium in rat hepatocytes. The glucose-6-phosphate independent activities of glycogen synthase in extracts of calcium-replete and calcium-depleted tissue approached the same value following the exposure to crude phosphoprotein phosphatase. The activities of glycogen phosphorylase decreased in calcium-depleted tissues and cells. Insulin stimulated the activity of glycogen synthase in muscle and fat in the absence of added sugar and in the absence of extracellular calcium. It is concluded that glycogen synthase is under the control of calcium in the three main glycogen storage tissues. The actions of calcium are probably mediated through the actions of calcium-sensitive protein kinase(s). 相似文献
813.
Z A Wojciechowski J Zimowski J G Zimowski A Lyznik 《Biochimica et biophysica acta》1979,570(2):363-370
1. Sinapis alba L. seedlings contain glycosyltransferase catalyzing the synthesis of sterol glucosides in the presence of UDPglucose as sugar donor. The major activity occurs in the membranous fraction sedimenting at 300--9000 x g. Successive treatment of the particulate enzyme fraction with acetone and Triton X-100 affords a soluble glucosyltransferase preparation which can be partly purified by gel filtration on Sephadex G-150. Molecular weight of the glucosyltransferase is 1.4 . 10(5). Apparent Km values for UDPglucose and sitosterol are 8.0 . 10(-5) M and 5.0 . 10(-6) M, respectively. 2. Comparison was made of the S. alba glucosyltransferase with a similar sterol-glucosylating enzyme isolated from non-photosynthesizing organism Physarum polycephalum (Myxomycetes). UDPglucose was the most efficient glucose donor in both cases but the enzyme from Ph. polycephalum can also utilize CDPglucose and TDPglucose. Glucose acceptors are, in case of both enzymes, sterols containing a beta-OH group at C-3 and a planar ring system (5 alpha-H or double bond at C-5). The number and position of double bonds in the ring system and in the side chain, as well as the presence of additional alkyl groups in the side chain at C-24 are of secondary importance. 3. The present results indicate that both enzymes can be regarded as specific UDPglucose:sterol glucosyltransferases. Certain differences in their specificity towards donors and acceptors of the glucosyl moiety suggest, however, a different structure of the active sites in both enzymes. 相似文献
814.
Sequential medical trials involving paired data 总被引:2,自引:0,他引:2
815.
816.
Through the work of U. J. Lewis and E. V. Cheever (1967, Endocrinoloyg81, 1338–1348) and U. J. Lewis, E. V. Cheever, and B. K. Seavey (1968, J. Biol. Chem.243, 260–267) it has been known for a number of years that human growth hormone (hGH), and many other proteins, reacts with unsaturated fatty acids to give rise to species with enhanced electrophoretic mobility. In view of the possible importance of this reaction in the genesis of charge isomeric protein artifacts, and for the understanding of hGH as a system of multiple isomers with distinct, and in some cases enhanced, specific activities, the nature of this reaction was investigated further. It was found that (1) the positions of oleic acid and growth hormone on polyacrylamide gel electrophoresis (PAGE) are coincident, indicating that the reaction leads to binding of the fatty acid to the protein: (2) the increment in molecular net charge on growth hormone is proportional to the molar ratio between the reactants, oleic acid and hGH; (3) the binding is noncovalent since it reverses under conditions of isoelectric focusing; (4) the reaction product has a molecular size indistinguishable from that of the reactant, hGH, by the criteria of “quantitative” PAGE (however, the reaction product exhibits an elevated negative molecular net charge in PAGE at pH 10.2); (5) the apparent isoelectric points of the hormone and its reaction products with oleic acid are indistinguishable in isoelectric focusing; (6) the interaction does not seem to involve the carboxyl charges on oleic acid since it is independent of ionic strength; (7) a noncovalent hydrophobic interaction with the protein is indicated since the range of electrophoretic mobilities exhibited by the hGH-oleic acid complex is smaller in the presence of benzyl alcohol in the gel than that exhibited by controls in it absence; (8) the reaction does not seem to involve free radical derivatives of the unsaturated fatty acid since it is not altered when the polyacrylamide gel is in a nonoxidative state; (9) the effect of the reaction with oleic acid on the tryptophan spectrum reflects only nonspecific interaction of the hormone-concomitant tryptophan perturbation. 相似文献
817.
A selective and diagnostic medium for ammonia oxidising bacteria 总被引:2,自引:0,他引:2
818.
J. Vlasák 《Biologia Plantarum》1981,23(6):406-413
Cell nuclei have been released from various plant tissues (barley leaves, roots and embryos, tobacco leaves and tissue cultures,Vicia faba roots,Arabidopsis thaliana leaves) by several homogenization methods and the optimal method was established for each tissue. The effect of the composition
of isolation medium on the yield and appearance of isolated nuclei was also studied. Longer incubation withn-octanol increases the yield considerably in most cases. Low concentrations of osmoticum increase the yield and their adverse
effect on the integrity of nuclei is of little significance. Gum arabic has a favourable effect on nuclei isolation from roots
only. 相似文献
819.
820.
A method for enzyme immunoassay of thyroid-stimulating hormone (TSH) is described, TSH was conjugated with horseradish peroxidase according to periodate oxidation method. Separation of the bound and free was obtained by double-antibody solid-phase technique using Sepharose 4B-anti-rabbit immunogiobulin G (IgG)-geat IgG. The fluorescence reaction using tyramine and hydrogen peroxide as substrates was used for the determination of enzyme activity in order to increase the sensitivity of enzyme immunoassay. The standard curve for serum TSH was satisfactory to recognize TSH concentrations as 0.06 μU/tube. TSH values obtained by this method correlated well with those obtained by radioimmunoassay (r, 0.96). The coefficients of variation were 1.8 to 5.3% (within assay) and 5.1 to 10.5% (between assay). The method is about equal to radioimmunoassay with respect to sensitivity. Since it requires minimal equipment and is less expensive than radioimmunoassay, it is possible to perform routine assays even in laboratories with limited facilities. 相似文献