An opiate receptor-associated aminopeptidase that degrades enkephalins

During the purification of opiate receptor by affinity chromatography on wheat germ agglutinin-agarose, an aminopeptidase is coeluted with the receptor. Virtually all of both the enzyme and the receptor is retained on the hydroxylapatite column. The aminopeptidase functions optimally at neutral pH and is activated by Mn2+. The enzyme is sensitive to dithiothreitol, is inhibited by amastatin and bestatin, and is insensitive to puromycin. The enzyme seems to be linked to the receptor, since its activity is enhanced by D-Ala2-Met-enkephalinamide or naltrexone. The properties of this aminopeptidase indicate that it is distinct from neutral arylamidase, leucine-aminopeptidase, aminopeptidases A and B, brain acidic aminopeptidase, and the membrane aminoenkephalinase that we purified recently (4).