An Aminopeptidase from Mouse Brain Cytosol That Cleaves N‐Terminal Acidic Amino Acid Residues

Abstract: An aminopeptidase with specificity directed toward peptides with acidic N‐terminal amino acid residues has been isolated from mouse brain cytosol. Purification by ion‐exchange chromatography and gel filtration resulted in an enzyme that hydrolyzed aspartyl‐phenylala‐nine methyl ester at a rate of 13.2 μu,mol/min/mg protein at pH 7.5, an increase in specific activity of 1000‐fold over that of brain homogenate. Its apparent molecular weight, determined by gel filtration, is ˜450,000. Dipeptides with N‐terminal aspartyl residues are cleaved preferentially to glutamic‐containing analogs, and a neutral amino acid (or histidine) is necessary in the adjacent position. For pep‐tides of the form aspartyl‐X, relative activity was 100, 81, 71, 66, 19, or 0, where X was alanine, serine, leucine, phenylalanine, histidine, or proline, respectively. Tripep‐tides were more rapidly hydrolyzed than dipeptides; however, activity tended to decline with increasing chain length. The acidic aminopeptidase can account for almost all of the activity of brain cytosol toward the N‐terminal aspartyl residue of angiotensin II, aspartyl‐phenylalanine methyl ester or aspartyl‐alanine, and the N‐terminal glu‐tamyl residue of adrenocorticotropin(5‐10). The enzyme was unaffected by bestatin or amastatin. It was inhibited by o ‐phenanthroline and EDTA. The latter effect could be reversed completely by Zn 2+ and partially by Mn 2+ or Mg 2+ ; Co 2+ and Fe 2+ had no effect; Ca 2+ was inhibitory. These properties distinguish the brain acidic aminopeptidase from aminopeptidase A isolated from human serum or pig kidney and the aspartyl aminopeptidase of dog kidney.