Isolation and characterization of a 60-residue intestinal peptide structurally related to the pancreatic secretory type of trypsin inhibitor: influence on insulin secretion.

We have isolated from pig intestine a 60-residue polypeptide initially identified by its inhibition of glucose-induced insulin secretion from perfused pancreas. The amino acid sequence of this porcine polypeptide was determined and found to be markedly similar to that of the pancreatic secretory trypsin inhibitor (41% residue identities). Furthermore, the disulfide arrangements of these two proteins appear identical, suggesting related overall conformations. However, the polypeptide, now named PEC-60 (peptide with N-terminal glutamic acid, C-terminal cysteine, and a total of 60 residues), was found not to inhibit trypsin. The amino acid sequence is also similar to that of a peptide recently isolated from rat bile/pancreatic juice which stimulates the release of cholecystokinin. The biological role of PEC-60 is not known, but the effect on insulin secretion and the homologies observed suggest important biological activities and interesting structural relationships.