The enzyme stability of dehydro-enkephalins

Dehydro-enkephalins [delta Ala2]-, [delta Ala3]-, [delta Phe4]-, and [delta Leu5]enkephalins, were examined for their stability to enzymatic hydrolysis by carboxypeptidase Y [EC 3.4.16.1]. The successively liberated amino acids were determined quantitatively by amino acid analyses. The saturated leucine-enkephalin was rapidly hydrolyzed from the COOH-terminus. However, peptide linkages with alpha, beta-dehydroamino acid residues placed in the enkephalin molecule were strongly resistant to the enzyme at the carboxyl side and completely resistant at the amino side of the dehydro residue.