Complementary peptide to the carboxyl-terminal tetrapeptide of gastrin

Codons of noncoding DNA strands for peptides have been found to code for amino acids with hydropathic properties opposite to those of the native peptides. Synthetic peptides, designated as complementary peptides, with amino acid sequences coded by noncoding DNA strands of several peptide hormones have been shown to bind the native peptides. In some instances, antibodies to these complementary peptides have shown agonist or antagonist properties of the native hormones. In this study a peptide was synthesized based on codons complementary to messenger RNA for the carboxyl-terminal gastrin tetrapeptide. This complementary peptide bound radiolabeled human gastrin (G17). Antibodies to the complementary peptide competitively inhibited the binding of 125I-gastrin by canine fundic mucosal membrane preparations. These antibodies also showed gastrin agonist properties in that they stimulated canine gastric mucosal parietal cell [14C]aminopyrine uptake, used as an index of stimulation of gastric acid secretion. Competitive inhibition of 125I-gastrin binding by membrane receptors for gastrin and stimulation of [14C]-aminopyrine uptake by antibodies to the complementary peptide for the gastrin tetrapeptide are consistent with their recognition, binding, and occupancy of gastrin receptors.