Demonstration of a beta-casomorphin immunoreactive material in the plasma of newborn calves after milk intake.

Blood was collected from newborn calves before and after their first milk intake after birth; extracts of plasma were assayed by radioimmunoassay for the presence of beta-casomorphin-7 immunoreactive materials. No beta-casomorphin immunoreactivity was found in samples collected before milk ingestion; however, in samples collected after milk ingestion a beta-casomorphin-7 immunoreactive material was detected. Chromatographic characterization showed that this material was not identical with beta-casomorphin-7 but might rather represent a precursor thereof. The material proved resistant to enzymatic attack during a 30-min incubation period at 37 degrees C in the plasma of newborn calves, whereas beta-casomorphin-7 was degraded under these conditions. A physiological significance of beta-casomorphin-7 eventually cleaved from such a precursor material at any site in the newborn mammal is suggested.

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compatible with the finding that beta-casomorphin (beta-CM) analogues in which the proline residue in position two has been replaced by D-alanine, seem to be completely resistant to enzymatic attack in the plasma.