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

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 Km and kcat values for this enzyme for lysyl-bradykinin were 57 mumol/l and 3000 min-1, respectively. The corresponding values for this enzyme for methionyl-lysyl-bradykinin were calculated to be 49 mumol/l and 16000 min-1, respectively. Bradykinin itself is extremely resistant to hydrolysis by this pancreatic enzyme.