Chemical modification of the monkey brain cytosolic aminopeptidase that cleaves enkephalin to its constituent amino acids. Evidence for essential tyrosine residue (residues)

Abstract

A cytosolic monkey brain aminopeptidase is known to cleave amino acids sequentially from the amino termini of peptides like enkephalins, angiotensins, and tuftsin. This enzyme is stimulated by ATP-Mg2+ and inactivated by cyclic AMP-dependent phosphorylation. Chemical modification of this aminopeptidase by several amino acid-modifying agents indicated essential lysine, histidine, arginine, cysteine, and tyrosine residues. The involvement of tyrosine residues in the catalytic activity was confirmed by modification by N-acetylimidazole and acetic anhydride, hydroxylamine treatment, and absorbance studies. Moreover, acetic-1-14C anhydride could label the enzyme that was inhibited by ATP or by bestatin, a competitive inhibitor of the enzyme.