Structure Antigenicity Relationships of Glucagon and Related Peptides

Abstract

Antisera specific for pancreatic glucagon and cross-reacting antisera have been used to characterise specific antigenic determinants in pancreatic glucagon, and those which are shared with gut glucagon-like substances (gut GLI). The reactions of glucagon, gut GLI, glucagon tryptic peptides 1-17 and 18-29, the related peptides Secretin and Cholecystokinin-pancreozymin (CCK-PZ) and Caerulein, were compared.

Glucagon-specific antisera react weakly with the N-terminal (1-17) and C-terminal (18-29) portions of pancreatic glucagon. Equimolar mixture of these two peptides results in greater immunoreactivity than the individual peptides but does not restore total immunoreactivity, suggesting an antigenic determinant in the region of the 17-18 aminoacid sequence.

Antiserum which cross-reacts with gut GLI also recognises glucagon peptides 1-17 and 18-29 and various other gut peptides assayed have structural similarities with the N-terminal and C-terminal peptide portions of glucagon. Equimilar mixture of the tryptic peptides restores total activity to that of pancreatic glucagon, suggesting that there are critical requirements in the peptide configuration for complete reaction with the pancreatic glucagon specific antiserum.

Key words

Immunoassay - Pancreatic Glucagon - Gut GLI - Tryptic Peptides and Secretin