PURIFICATION AND CHARACTERIZATION OF ENKEPHALIN-RELATED PEPTIDES RELEASED BY IN-VITRO PEPTIC DIGESTION OF BOVINE PLASMA-PROTEINS

In vitro pepsin treatment of plasma proteins generates biologically ac tive peptides such as enkephalin-related peptides. These peptides were characterized using chromatographic techniques along with a radioimmu noassay procedure involving the use of Leu-enkephalin and Met-enkephal in antisera. Serum albumin is the only existing source of Met-enkephal in-immunoreactive peptides. One of these peptides consists of nine res idues with the sequence NH2-Glu-Lys-Leu-Gly-Glu-Tyr-Gly-Phe-Gln; a sec ond immunoreactive peptide might be the hexapeptide NH2-Gly-Glu-Tyr-Gl y-Phe-Gln, which has been already identified in a rat serum albumin hy drolysate. Our results indicate that immunoglobulins constitute the ma in source of Leu-enkephalin-immunoreactive peptides. Immunoreative NH2 -Tyr-Phe-Leu was isolated from pepsin-treated bovine immunoglobulins. Binding experiments and cyclic nucleotide measurements suggested that this peptide was an enkephalin-related peptide. Similar experiments co uld be carried out to identify the proteins that contain enkephalin-li ke peptide sequences with the view to investigating the various biolog ical processes occurring in enzymatically treated proteins.