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Summary: The supernatant extracts from disrupted Escherichia coli had only low hydrolytic activity towards diglycine, divaline and prolylglycine, but latent peptidases were activated by Co2+ or Mn2+. The cations K+, Mg2+, Zn2+, Fe2+, Ni2+, Cu2+ Ca2+ and Cd2+ caused no increase in peptidase activity while Cd2+, Zn2+ and Cu2+ antagonized the effects of Co2+ and Mn2+. Measurements of optimum cation concentration, of pH optimum and of effects of various buffers led to the conclusion that the main peptidase activity towards these three peptides, and towards a broad spectrum of other dipeptides, resided in a single Co2+ activated enzyme. The activity of this peptidase was enhanced by phosphate and inhibited by veronal. Similar measurements with Mn2+ suggested the presence of several enzymes with lower activities and narrower substrate specificity than the Co2+ activated peptidase. Procedures were devised for the assay, under optimum conditions, of the main peptidase activities of a crude extract.
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