Action of human pancreas alanine aminopeptidase on biologically active pep tides: kinin converting activity

Abstract

A group of 15 biologically active peptides were studied with respect to their susceptibility to chain shortening by human pancreas alanine aminopeptidase. Those susceptible were somatostatin, melanocyte stimulating hormone, fibrinopeptide A, eosinophilotactictetrapeptide, lysyl-bradykinin, and methionyl-lysyl-bradykinin. The latter two were selected for further study. Direct identification and determination of the reaction products, lysine and/or methionine, were undertaken to establish unequivocally the kinin-converting activity of human pancreas alanine aminopeptidase, which exhibited a pH optimum at pH 7.9. The K m and k cat values for this enzyme for lysyl-bradykinin were 57 μmol/l and 3000 min −1, respectively. The corresponding values for this enzyme for methionyl-lysyl-bradykinin were calculated to be 49 μmol/l and 16000 min −1, respectively. Bradykinin itself is extremely resistant to hydrolysis by this pancreatic enzyme.