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91.
The role of uptake hydrogenase in providing reducing power to nitrogenase was investigated in Rhizobium leguminosarum bacteroids from nodules of Pisum sativum L. (cv. Homesteader). H2 increased the rate of C2H2 reduction in the absence of added substrates. Malate also increased nitrogenase (C2H2) activity while decreasing the effect of H2. At exogenous malate concentrations above 0.05 mM no effect of H2 was seen. Malate appeared to be more important as a source of reductant than of ATP. When iodoacetate was used to minimize the contribution of endogenous substrates to nitrogenase activity in an isolate in which H2 uptake was not coupled to ATP formation, H2 increased the rate of C2H2 reduction by 77%. In the presence of iodoacetate, an ATP-generating system did not enhance C2H2 reduction, but when H2 was also included, the rate of C2H2 reduction was increased by 280% over that with the ATP-generating system alone. The data suggest that, under conditions of substrate starvation, the uptake hydrogenase in R. leguminosarum could provide reductant as well as ATP in an isolate in which the H2 uptake is coupled to ATP formation, to the nitrogenase complex. 相似文献
92.
Nanosecond laser flash photolysis has been used to produce and identify the vitamin K semiquinone (radical) from vitamin K dihydroquinone and to observe its formation and decay in the presence of vitamin K-dependent carboxylase (epoxidase). The activity of vitamin K-dependent carboxylase is not decreased by exposure to the laser. Absorbance of the semiquinone is proportional to enzyme concentration and is stimulated by a synthetic substrate, PheLeuGluGluIle. Stabilization of the semiquinone is observed in the presence of the enzyme. The semiquinone is rapidly destroyed in the presence of inhibitors of vitamin K-dependent carboxylase and vitamin K epoxidase. 相似文献
93.
Ronald I. Clyman Louise Wong Michael A. Heymann Abraham M. Rudolph 《Prostaglandins & other lipid mediators》1978,15(2):325-331
The relative potencies of the prostaglandins A1, A2, E1, E2, F2α and their 15-keto-, 15-keto-13,14-dihydro-, and 13,14-dihydro-metabolites were investigated on isolated lamb ductus arteriosus preparations contracted by exposure to elevated PO2. All the prostaglandins (except PGF2α and its 15-keto-metabolites) relaxed the tissue. However, only PGE1, E2, and their 13,14-dihydro-metabolites, were effective at concentrations below 10−8 M. Therefore, events that alter metabolism of circulating PGs in the perinatal period may have significant effects on the relative patency or closure of the ductus arteriosus. 相似文献
94.
Increased Spontaneous Mitotic Segregation in Mms-Sensitive Mutants of SACCHAROMYCES CEREVISIAE 下载免费PDF全文
Methyl methanesulfonate (MMS)-sensitive mutants of Saccharomyces cerevisiae belonging to four different complementation groups, when homozygous, increase the rate of spontaneous mitotic segregation to canavanine resistance from heterozygous sensitive (canr/+) diploids by 13-to 170-fold. The mms8-1 mutant is MMS and X-ray sensitive and increases the rate of spontaneous mitotic segregation 170-fold. The mms9-1 and mms13-1 mutants are sensitive to X rays and UV, respectively, in addition of MMS, and increase the rate of spontaneous mitotic segregation by 13-fold and 85-fold, respectively. The mutant mms21-1 is sensitive to MMS, X rays and UV and increases the rate of spontaneous mitotic segregation 23-fold. 相似文献
95.
D A Carson S Lawrance M A Catalano J H Vaughan G Abraham 《Journal of immunology (Baltimore, Md. : 1950)》1977,119(1):295-300
Although IgG rheumatoid factor may play a central role in the pathogenesis of rheumatoid arthritis, previously there have been no precise methods for its specific measurement in serum and synovial fluid. This paper describes a solid phase radioimmunoassay for the independent quantification of IgM and IgG rheumatoid factor reacting with the Fc fragment of human IgG. As measured by this assay, serum IgG rheumatoid factor levels differed significantly between patients with seropositive and seronegative rheumatoid arthritis and normal control subjects. In addition, several sera and joint fluids from patients with seropositive rheumatoid arthritis, even without vasculitis, were shown by gel chromatography to have acid-dissociable complexes of IgG rheumatoid factor suggestive of IgG-IgG dimer or trimer formation. 相似文献
96.
Properties of particulate and solubilized phosphatidylserine synthase activity from Saccharomyces cerevisiae. Inhibitory effect of choline in the growth medium 总被引:14,自引:0,他引:14
When radiolabeled serine is incubated with a particulate fraction from Saccharomyces cerevisiae, radioactivity is incorporated initially into phosphatidylserine and gradually appears in phosphatidylethanolamine. Because decarboxylation of phosphatidylserine is blocked by hydroxylamine, phosphatidylserine synthase can be assayed separately. The yeast phosphatidylserine synthase activity 1) exhibits a divalent cation requirement; 2) is stimulated by exogenous CDP-diolein (apparent Km = 0.17 mM); 3) has an apparent Km = 4 mM for L-serine; 4) has a neutral pH optimum; 5) is inhibited by p-hydroxymercuribenzoate; and 6) is reversible in the presence of 5'-CMP, but not 2'-CMP, 3'-CMP, or 5'-AMP. The phospholipid-synthesizing activity is solubilized with Triton X-100 and the enzymatic parameters have been compared with the particulate form of the enzyme. Detergent extracts catalyze the conversion of exogenous purified [31P]CDP-diglyceride to [32P]phosphatidylserine in the presence of Mn2+ and L-serine. Enzyme preparations from cells grown in the presence of choline, that have reduced phospholipid methylation activity (Waechter, C. J., Steiner, M. R., and Lester, R. L. (1969) J. Biol. Chem. 244, 3419-3422), also have substantially less phosphatidylserine synthase activity compared to identical preparations grown in the absence of choline. When choline, phosphocholine, CDP-choline, and phosphatidylcholine are present in vitro, there is no direct inhibitory effect on phosphatidylserine synthase activity. While the inclusion of choline in the growth medium caused a significant reduction in phosphatidylserine synthase activity, it did not appreciably effect the apparent Km values for L-serine and CDP-diglyceride. These results are consistent with choline-grown cells containing less phosphatidylserine synthase activity because of lower amounts of enzyme present or perhaps less active enzyme due to covalent modification. 相似文献
97.
Influence of free fatty acid anion on the binding of warfarin to cytoplasmic proteins from rat liver
Louise Charest-Boule Saroj Chakrabarti Jules Brodeur 《Chemico-biological interactions》1980,29(1):85-94
In vitro binding studies have shown that warfarin binds strongly to both ligandins (Y) and Z protein obtained from rat liver cytosol with dissociation constants of 11.7 and 10.1 μM respectively. Increasing concentrations of oleate ion significantly increased the dissociation constant of warfarin with either protein, whereas laurate ion showed the same behavior only with Z protein. On the other hand, the binding of warfarin to liver cytoplasmic proteins in vivo was decreased in 72-h-pre-fasted rats, although such fasting failed to produce any increase in the in vivo levels of the cytoplasmic free fatty acids (FFA). However, based on the results of the in vitro binding study, it is suggested that changes in the composition of hepatic cytoplasmic free fatty acids as a result of fasting could reduce the in vivo binding of warfarin to Y and Z proteins and hence could lead to an increase of unbound warfarin in liver cytosol. 相似文献
98.
99.
Michel Roberge Gilles Grondin Louise Larose Adrien R. Beaudoin 《Cell and tissue research》1981,220(4):781-786
Summary Stimulation of the exocrine pancreas by the secretagogue urecholine causes degranulation of the acinar cells. Under in vivo conditions, this degranulation is not uniform throughout the tissue. Indeed some of the acini are almost completely depleted of their granules while others display the appearance of resting acini. A noticeable feature is that all the cells of the same acinus display a comparable degree of degranulation. Moreover, groups of neighbouring acini seem to respond simultaneously suggesting that the secretory stimulus is propagated from one acinus to the other. In vitro stimulation of dispersed acini also showed that some of the acini are more responsive than others indicating that this phenomenon can not be attributed to accessibility of the secretagogue to its receptor. These observations lead us to the concept that the response of the pancreatic acinar cell is controlled at the level of the acinus. 相似文献
100.