IDENTIFICATION BY SPECIFIC RADIOIMMUNOASSAY OF 2 NOVEL PEPTIDES DERIVED FROM THE C-TERMINUS OF PORCINE PREPROGASTRIN

A radioimmunoassay was developed using antibodides to a synthetic analog of the C-terminal hexapeptide sequence of the porcine gastrin precursor. Boiling H2O extracts of porcine antral mucosa contained immunoreactive material that diluted in parallel with standard peptide. Concentrations of immunoreactivity were 5.5 .+-. 0.8 nmol .cntdot. g-1 in antral mucosa and were closely similar to those of C-terminal heptadecapeptide gastrin immunoreactivity (5.0 .+-. 9.6 nmol .cntdot. g-1); .apprx. 30-fold lower concentrations were found in porcine duodenum. A similar distribution was found in ferret, but human, rat and chicken antrum did not contain significant quantities of immunoreactivity. Gel filtration of porcine antral extracts of Sephadex G-50 revealed a single peak of immunoreactivity eluting in a similar position to G17, but on anion-exchange chromatography 2 peaks of immunoreactive material were separated. These also differed in their retention time on reverse phase HPLC. Both peptides are probably derived by tryptic cleavage at the C-terminus of porcine preprogastrin. No evidence suggested that there are significant quantities of unprocessed preprogastrin in hog antral mucosa. The precise chemical difference between the 2 immunoreactive peptides identified here remains to be established; together, however, they provide specific markers for progastrin synthesis.