Isolation, sequence and biosynthetic significance of a novel fragment of gastrin-releasing peptide from chicken proventriculus.

The isolation of bombesin-related peptides in chicken proventriculus was monitored by radioimmunoassay using a C-terminal specific bombesin antibody. Two peptides were identified, one corresponded to the 27-residue, chicken gastrin-releasing peptide (GRP-27) previously identified; the other corresponded to its C-terminal hexapeptide. Chicken GRP-27 stimulated pancreatic and gastric acid secretion in anaesthetized turkeys, but the hexapeptide was inactive. No evidence could be found to suggest that the hexapeptide was an artifact of degradation generated during extraction or isolation. It is proposed that the hexapeptide is produced either by chymotryptic-like cleavage of GRP-27 or by trypsin-like cleavage followed by two cycles of dipeptidylaminopeptidase cleavage. This type of biosynthetic processing may be more common than formerly supposed.