Heterogeneity of the gastrins in blood and tissue.
The forms of gastrin which have been isolated from antral mucosa or Zollinger-Ellison tumour tissue (or both) and characterized chemically are as follows: little gastrin (G17) (LG); big gastrin (G34) (BG); minigastrin (G13); the NH2-terminal 1-13 fragment of G17. All these exist as pairs of peptides which have an identical amino acid sequence and differ solely in that the single tyrosyl residue present may be sulphated. The proportions of the pairs of each peptide show species variation where isolation has been accomplished (e.g. from hog, dog, cat, cow, sheep and man in the case of LG, and hog and man for BG). All these forms of the hormone have been identified immunologically in serum; LG and BG have been identified in duodenal mucosa. Two larger forms of the hormone have been identified immunologically in serum; component I (CI) and 'big big gastrin' (BBG). Material corresponding in size to BBG and CI has been identified in extracts of antral and jejunal mucosa and Zollinger-Ellison tumour. Neither BBG nor CI has been characterized chemically to date and their physiological significance is uncertain. Recent studies suggest that the heterogeneity of gastrins in serum and tissues may be considerably greater than is indicated by the list of components given above.