Human pancreatic icosapeptide: Is immunocytochemical localization ol fragment of the pancreatic polypep

In dogs, the COOH-terminal part of the pan- creatic polypeptide precursor gives rise to a stable icosapeptide product against which an antiserum has been raised. By im- muhohistochemistry, icosapeptide immunoreactivity was lo- calized in human pancreas exclusively to cells that also stored pancreatic polypeptide. Analytical peptide chemistry demon- strated that a peptide corresponding to the canine icosapeptide could be extracted from the pancreatic polypeptide-rich duo- denal part of the human pancreas. The human pancreatic ico- sapeptide was isolated by acid ethanol extraction, gel filtta- tion, anion-exchange chromatography, and reverse-phase' high-performance liquid chromatography. The COOH-termi- nal sequence of the human icosapeptide is very similar to that of the canine icosapeptide, whereas none of the first nine ami- no acid residues are identical. When the primary structure of peptides from three different species are compared, it is appar- ent that the pancreatic polypeptide part of the common pre- cursor is a. ell-conserved sequence as compared to the icosa- peptide part, although 8 out of 11 residues in the COOH-ter- minal sequence of the icosapeptide are identical in all three