Substrate specificity of aminopeptidase Ey from hen's (Gallus domesticus) egg yolk

1. Aminopeptidase Ey, purified from the egg yolk of the hen (Gallus gallus domesticus), was studied for its specificity against oligopeptides at pH 7.5. The enzyme has a broad specificity for amino acid residues at P1 position. 2. The enzyme hydrolyzed N-terminal Xaa-Pro bonds in chicken brain peptide (Leu-Pro-Leu-Arg-PheNH2), substance P fragment 1-4 (Arg-Pro-Lys-Pro) and bradykinin fragment 1-5 (Arg-Pro-Pro-Gly-Phe), but did not hydrolyze substance P (Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-MetNH2) or bradykinin (Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg). 3. The enzyme released proline from Pro-Phe-Gly-Lys, while it was unable to release proline from melanocyte, stimulating the hormone release-inhibiting factor (Pro-Leu-GlyNH2) and schistoFMRF-amide (Pro-Asp-Val-Asp-His-Val-Phe-Leu-Arg-PheNH2).