Structure of Porcine Cholecystokinin‐Pancreozymin

TLDR

Cholecystokinin‑pancreozymin is a peptide whose partial amino‑acid sequence (Lys‑Arg‑Val‑Lys‑Asn‑Arg‑Ile‑Arg‑Asp‑Phe‑NH₂) is largely identical to the corresponding region of caerulein, with a methionine replacing a threonine and its sole tyrosine esterified with sulphuric acid. Trypsin cleaves all four peptide bonds of cholecystokinin‑pancreozymin except the arginyl‑valine bond, which is cleaved by thrombin, yet both the resulting C‑terminal heptacosapeptide and the tryptic octapeptide retain strong cholecystokinin and pancreozymin activity.

Abstract

Cholecystokinin‐pancreozymin has been found to have the partial structure Lys (Ala 1 , Gly 1 , Pro 1 , Ser 1 ) · Arg · Val (Ile 1 , Met 1 , Ser 1 ) Lys · Asn (Asx 1 , Glx 1 , His 1 , Leu 2 , Pro 1 , Ser 2 ) Arg. Ile (Asp 1 , Ser 1 ) Arg · Asp [Gly 1 , Met 2 , Trp 1 , Tyr (SO 3 H)] Asp · Phe · NH 2 . Of the four peptide bonds in this polypeptide, three arginyl and one lysyl, that are cleaved by trypsin only the arginyl‐valine bond is cleaved by thrombin, with retention of the cholecystokinin and pancreozymin activities of the original molecule in the C‐terminal heptacosapeptide. The C‐terminal tryptic octapeptide too has strong cholecystokinin and pancreozymin activity. Except for the replacement of a threonine with methionine the eight amino acid units of this peptide are the same as those that comprise the corresponding part of the molecule of caerulein. Also like that in caerulein, the phenolic group of the only tyrosine of cholecystokinin‐pancreozymin is esterified with sulphuric acid.