Bacillus subtilis aminopeptidase: Specificity toward amino acid amides, dipeptides, and oligopeptides

Bacillus subtilis aminopeptidase hydrolyzed amino acid amides with a specificity similar to that determined using amino acyl-β-naphthylamides, but at much greater catalytic rates. Neutral and basic amino acid amides were the best substrates. A series of Leu and Lys NH 2-terminal dipeptides hydrolyzed by Co 2+-activated aminopeptidase showed that the k cat K m ratios for the Lys substrates were fourfold greater than the corresponding Leu substrates and that catalytic differences reflected the identity of COOH terminal residues. Greatest catalytic rates were obtained when aromatic residues were in the COOH terminal position of the substrate (Trp, Tyr, Phe); but, significant hydrolysis was achieved when aliphatic residues were COOH-terminal in the dipeptide. The Co 2+-activated enzyme would not hydrolyze peptide bonds composed of the imide nitrogen of Pro, thus, bradykinin was not a substrate. However, the Co 2+-activated enzyme removed sequentially the first four residues from eledoisin-related peptide and the A chain of bovine insulin.