Purification and characterization of an enkephalin-degrading aminopeptidase from guinea pig serum

An enkephalin-degrading aminopeptidase using Leu-enkephalin as a substrate was purified about 4100-fold from guinea pig serum. The purified preparation was apparently homogenous, showing one band on polyacrylamide gel electrophoresis. The molecular weight of the enzyme was approx. 92 000. The aminopeptidase had a pH optimum of 7.0 with Km values of 0.12 mM and 0.18 mM for Leu- and Met-enkephalin, respectively. The enzyme hydrolyzed neutral, basic and aromatic amino acid beta-naphthylamides, but did not the acidic one. The enzyme was inhibited strongly by metal-chelating agents, bestatin and amastatin and weakly by puromycin. Among several biologically active peptides, angiotensin III and substance P strongly inhibited the enzyme.