Additional Studies on the Nature of Big Big Gastrin

Abstract

Analyses by electrophoresis, ultracentrifugation, and gel filtration extend our previous finding of a new form of immunoreactive gastrin, designated as big (BBG). This component elutes in the void volume of Sephadex G-50 gel filtration, has the same ultracentrifugal sedimentation velocity as human growth hormone, and an electrophoretic mobility on starch gel just in advance of serum albumin. Trypsin converts BBG to smaller hormonal forms down to and including heptadecapeptide-like gastrin. BBG is a major fraction of total gastrin immunoreactivity in normal human, canine, and porcine plasmas in the nonstimulated state and is the only form detectable in a gastrectomized patient post-Billroth II. It is not detectably stimulated by feeding and comprised less than about 2% of the total immunoreactivity in a Zollinger-Ellison tumor or in the plasma of patients with Zollinger-Ellison syndrome, pernicious anemia, or who were gastrin hypersecretors. The biologic significance of BBG has not as yet been evaluated. A family of immunoreactive gastrins with elution volumes between BBG and the previously described big gastrin has been detected as a minor component of an extract of a Zollinger-Ellison tumor as well as after tryptic digestion of BBG. It has not been determined whether this family of gastrins is significant in vivo or simply represents degradation products of BBG.