PROLYL AMINOPEPTIDASES FROM PIG INTESTINAL-MUCOSA AND HUMAN LIVER - PURIFICATION, CHARACTERIZATION AND POSSIBLE IDENTITY WITH LEUCYL AMINOPEPTIDASE

Prolyl aminopeptidase (EC 3.4.11.5) has been assumed to be an enzyme catalyzing specifically the removal of unsubstituted NH2-terminal L-prolyl residues from various peptides. We purified the enzyme to apparent homogeneity from pig intestinal mucosa and human liver using L-prolyl-L-leucylglycinamide (melanostatin) as a substrate. Each purified enzyme appeared to be a 300 K dalton metalloenzyme, and to consist of six identical subunit polypeptides with a molecular weight of about 55,000 each, associating noncovalently. The intestinal enzyme had a pH optimum at about 10(4) and its kinetic study with various peptide substrates revealed a broad substrate specificity. The k(cat)/K(m) values for peptides with an NH2-terminal leucyl residue were about 10(4) times greater than those for peptides with an NH2-terminal prolyl residue. These molecular and enzymatic properties were essentially the same with those of leucyl aminopeptidase (EC 3.4.11.1), suggesting that prolyl aminopeptidase is identical with leucyl aminopeptidase.