Studies on the enzymatic degradation of beta-casomorphins

beta-Casomorphins (beta-CMs), although known to be highly resistant to proteolytic enzymes, are demonstrated to be rapidly degraded in bovine or rat plasma. Degradation of these peptides consisting of the amino acid sequence TYR-PRO-PHE-PRO-GLY-PRO-ILE and C-terminally shortened fragments thereof, may be due to an enzyme identical with or similar to the dipeptidyl-peptidase IV (DP IV) which is known to cleave dipeptide fragments from the N-terminus of peptides after proline residues. This assumption is compatible with the finding that beta-casomorphin (beta-CM) analogues in which the proline residue in position two has been replaced by D-alanine, seem to be completely resistant to enzymatic attack in the plasma.