AN AMINOPEPTIDASE ACTIVITY FROM PORCINE KIDNEY THAT HYDROLYZES OXYTOCIN AND VASOPRESSIN - PURIFICATION AND PARTIAL CHARACTERIZATION

An aminopeptidase from porcine kidney, hydrolyzing oxytocin and vasopr essin in vitro, was purified by chromatography on hydroxyapatite, DEAE -cellulose and nickel ion chelate gel and gel filtration on Sephadex G -100. The enzyme appeared to be a high molecular mass (M(r) 105 000) m onomeric protein. It was sensitive to inhibition by metal chelator, o- phenanthroline. Cobalt ion and sulfhydryl activator, 2-mercaptoethanol , had activating effects, while p-chloromercuribenzoate, amino acids w ith large hydrophobic side chains, L-cystine and aminopeptidase inhibi tors, bestatin and amastatin, had inhibitory effects on the enzyme act ivity. The enzyme hydrolyzed several aminoacyl p-nitroanilides, and ha d the highest specificity against S-benzyl-L-cysteine p-nitroanilide. The properties of the enzyme were distinct from those of well-characte rized leucyl aminopeptidase (EC 3.4.11.1), membrane alanyl aminopeptid ase (EC 3.4.11.2) and primate placental cystinyl aminopeptidase (EC 3. 4.11.3).