A new aminopeptidase in monkey cerebral membrane fraction: hydrolysis of enkephalin

A new aminopeptidase, which cleaves the Tyr1-Gly2 bond of enkephalin, was partially purified from the monkey brain membrane fraction. The molecular weight of the enzyme was estimated to be about 53,000, and the optimum pH was in the neutral region (pH 6.5). The enzyme hydrolyzed Leu-enkephalin with a Km value of 238 microM. It strongly hydrolyzed L-tyrosine and L-leucine beta-naphthylamide, but showed only weak affinity for L-arginine or L-alanine beta-naphthylamide. The enzyme was much more potently inhibited by bestatin (IC50: 2 x 10(-8) M) than the other specific aminopeptidase inhibitors examined, while it showed low sensitivity to puromycin and actinonin, inhibitors of cerebral enkephalin-degrading aminopeptidase and aminopeptidase M, respectively. These results indicate that the new enkephalin-degrading aminopeptidase is clearly distinct from aminopeptidase M, which has been reported to be a key enzyme in enkephalin inactivation.