A membrane-bound aminopeptidase isolated from monkey brain and its action on enkephalin

A membrane-bound aminopeptidase which cleaves the tyrosine-glycine bond of enkephalin was purified about 1600-fold from monkey brain. This aminopeptidase hydrolyzed Leu-enkephalin with a Km value of 35 microM and also hydrolyzed basic, neutral and aromatic amino acid beta-naphthylamides. An apparently homogeneous enzyme consisted of a single polypeptide chain with a molecular weight of approx. 100 000. The optimum pH was in the neutral region. From the analysis of the reaction products, only aminopeptidase activity was detected. The enzyme was inactivated by metal chelators, but the activity could be restored by the addition of divalent cations, such as Co2+, Mg2+ and Zn2+. Puromycin, bestatin and amastatin, which are aminopeptidase inhibitors derived from microorganism, showed strong competitive inhibition of the enzyme, the most potent being amastatin, with a Ki value of 0.02 microM.