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551.
A rapid and sensitive microbial assay was developed to detect lethal products of aflatoxin B metabolism by rainbow trout (Salmon gairdneri) Mt. Shasta strain. Bacillus subtilis GSY 1057 (hisA1, uvr-1, metB4), a DNA repair deficient strain, was incubated for 20 min in the 20,000 times g supernate from trout liver homogenates which had been preincubated for 10 min with various levels of aflatoxin B. Serial dilutions of the incubation mixture were plated in triplicate on tryptose blood agar base plates and colonies were counted after 12 hr at 37 degrees C. One mumole aflatoxin B in 3.2 ml incubation mixture reduced viability 60%. 相似文献
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The uridine 5'-diphosphate-N-acetyl-d-glucosamine oxidoreductase activity of Citrobacter freundii ATCC 10053 was found to be located in the soluble cytoplasmic fraction of lysed spheroplasts. 相似文献
554.
The effect of pO2 on the monoamine oxidase activity of mitochondria from rabbit brain and liver was investigated using the substrates tyramine, dopamine, tryptamine and serotonin. The effect of the second substrate (oxygen) was dependent upon the concentration of the first substrate (the amine). At amine concentrations below 50 micronM, the reaction rate as measured by a radiometric assay, was not affected by variations in the pO2. It was found that both phenazine methosulfate (PMS) and chlorpromazine (CPZ) are reversible inhibitors of monoamine oxidase, the former was a potent inhibitor (Ki=3X10(-6) M) and the latter relatively weak (Ki=5X10(-4) M). Inhibition by both compounds was non-competitive with respect to the amine substrate. Imipramine was a weak inhibitor of purified MAO from beef kidney and of the MAO activity of mitochrondria from brain and liver. Using tyramine or dopamine as the substrate (0.5-1.0 mM), inhibition ranging from 6-30% was observed at 5X10(-4) M imipramine. With tryptamine or serotonin (0.5-1.0 mM) as the substrate in the presence of 5X10(-4) M imipramine the drug seemed to have no net effect on MAO activity since the average value in the presence of imipramine for a number of experiences was the same as the average for control experiments. For p-iodo-phenyl-3-p-nitrophenyl tetrazolium chloride, a Ki of 43X10(-6) M was found using dopamine as the substrate and oxygen as the gas phase. 相似文献
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The organization of the actin cytoskeleton can be regulated by soluble factors that trigger signal transduction events involving the Rho family of GTPases. Since adhesive interactions are also capable of organizing the actin-based cytoskeleton, we examined the role of Cdc42-, Rac-, and Rho-dependent signaling pathways in regulating the cytoskeleton during integrin-mediated adhesion and cell spreading using dominant-inhibitory mutants of these GTPases. When Rat1 cells initially adhere to the extracellular matrix protein fibronectin, punctate focal complexes form at the cell periphery. Concomitant with focal complex formation, we observed some phosphorylation of the focal adhesion kinase (FAK) and Src, which occurred independently of Rho family GTPases. However, subsequent phosphorylation of FAK and paxillin occurs in a Rho-dependent manner. Moreover, we found Rho dependence of the assembly of large focal adhesions from which actin stress fibers radiate. Initial adhesion to fibronectin also stimulates membrane ruffling; we show that this ruffling is independent of Rho but is dependent on both Cdc42 and Rac. Furthermore, we observed that Cdc42 controls the integrin-dependent activation of extracellular signal-regulated kinase 2 and of Akt, a kinase whose activity has been demonstrated to be dependent on phosphatidylinositol (PI) 3-kinase. Since Rac-dependent membrane ruffling can be stimulated by PI 3-kinase, it appears that Cdc42, PI 3-kinase, and Rac lie on a distinct pathway that regulates adhesion-induced membrane ruffling. In contrast to the differential regulation of integrin-mediated signaling by Cdc42, Rac, and Rho, we observed that all three GTPases regulate cell spreading, an event that may indirectly control cellular architecture. Therefore, several separable signaling pathways regulated by different members of the Rho family of GTPases converge to control adhesion-dependent changes in the organization of the cytoskeleton, changes that regulate cell morphology and behavior. 相似文献
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Maarit H. Lahtinen Emma Kynkäänniemi Ching Jian Anne Salonen Anne-Maria Pajari Kirsi S. Mikkonen 《Molecular nutrition & food research》2023,67(20):2300201