Characterization of a Dipeptidyl Aminopeptidase from Bovine Adrenal Medulla

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Abstract
A dipeptidyl aminopeptidase was partially purified from a supernatant fraction of bovine adrenal medulla by gel filtration and anion-exchange chromatography. From gel filtration, the apparent molecular weight of the enzyme was 68,100 and its pH optimum was 9.5. Its Km for hydrolysis of the synthetic substrate arginylarginine-.beta.-naphthylamide was 5.5 .times. 10-6 M. The enzyme was inhibited by metal ion chelating agents and thiol blocking agents, suggesting the requirement for both a metal ion and an active cysteine residue for its activity. Several peptides were cleaved by the dipeptidyl aminopeptidase involving the sequential removal of dipeptides from the N-terminus. Biologically active peptides, such a leucine-enkephalin, methionine-enkephalin, and angiotensin II, were hydrolyzed by the dipeptidyl aminopeptidase although opioid peptides with a length greater than five amino acid residues were not susceptible to hydrolysis. Other peptides with a blocked N-terminus (neurotensin, bombesin) or a proline residue adjacent to a potential cleavage site (substance P) were not hydrolyzed. The ability of this dipeptidyl aminopeptidase to degrade certain neuropeptides suggests that it could be involved in neuropeptide degradation.

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