Isolation and characterization of an enkephalin-degrading aminopeptidase from rat brain

An enkephalin-degrading aminopeptidase from rat brain extracts has been purified to apparent homogeneity. This enzyme cleaves the N-terminal tyrosine from Leu-enkephalin and hydrolyzes some beta-naphthylamides and p-nitro-anilides of neutral, basic and aromatic, but not acidic, amino acids. The enzyme requires a free amino group on the substrate and has a neutral pH optimum. After dialysis against EDTA, the enzyme requires a divalent cation (Zn2+, Co2+ greater than Mn2% greater than Mg2+) for activity. The enzyme is inhibited by puromycin, o-phenanthroline, p-chloromercuribenzoate and EDTA, but not by puromycin, methylsulfonyl fluoride or a specific peptide inhibitor of leucine amino-peptidase. The aminopeptidase consists of two subunits and has a molecular weight of about 100 000.