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991.
Herpes virus aotus: a latent herpesvirus from owl monkeys (Aotus trivirgatus) isolation and characterization 总被引:3,自引:0,他引:3
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Effect of rifampicin on stability and transfer of R-factors 总被引:1,自引:0,他引:1
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Homoserine kinase from Escherichia coli K-12: properties, inhibition by L-threonine, and regulation of biosynthesis 总被引:4,自引:1,他引:3 下载免费PDF全文
We have partially purified homoserine kinase from a genetically derepressed strain of Escherichia coli K-12. The optimum pH of the enzyme-substrate reaction was 7.8 and the K(m) values for l-homoserine and adenosine 5'-triphosphate were both 3 x 10(-4) M. K(+) (or NH(4) (+)) as well as Mg(2+) were required for its activity. The sedimentation coefficient determined by ultracentrifugation in a sucrose density gradient was 5.0 +/- 0.25S. l-Homoserine was an excellent protector against heat inactivation of homoserine kinase. l-Threonine was a competitive inhibitor of homoserine kinase, suggesting that end-product inhibition of this enzyme plays a role in vivo in the overall regulation of threonine biosynthesis. The specific activity of aspartokinase I-homoserine dehydrogenase I and of homoserine kinase showed a strong positive correlation in extracts from strains under widely varying conditions of genetic or physiological derepression; it was concluded that these two enzymes are coordinately regulated in E. coli K-12. 相似文献
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Summary A direct immunohistochemical method of high specificity is presented for the demonstration of sites of cathepsin B1. Antisera were raised in rabbits against pure enzyme preparations. The specific antibodies were subsequently isolated and labelled according to methods previously published. Sections from tissues specially rich in this enzyme like liver, kidney, intestinal epithelia and the active macrophages of talcum granulomas were studied. The results suggest a localization of this enzyme mainly to lysosomal organelles and phagocytic vacuoles, which are known from chemical data to contain this enzyme. The prerequisite for a positive tissue reaction is that the enzyme must be present in a form available for antigen-antibody interaction. 相似文献