Measurement of precursors for alpha-amidated hormones by radioimmunoassay of glycine-extended peptides after trypsin-carboxypeptidase B cleavage.

Using fragment 5-17 of human gastrin-17 extended with glycine at the C-terminus as hapten, three of six rabbits produced high-titer, high-avidity antisera specific for glycine-extended gastrins. In combination with trypsin and carboxypeptidase B cleavage, radioimmunoassays based on these antisera measured progastrins in some extra-antral tissues and certain malignant tumors. The results show that sequential cleavage with trypsin and carboxypeptidase B followed by radioimmunoassay of glycine-extended peptides is a rapid and accurate procedure for measurement of biosynthetic precursors of alpha-amidated peptide hormones. Moreover, the procedure seems promising in the search for tumor markers.