NH2-terminal monoiodination of hexadecapeptide gastrin: a simple procedure for preparation of 125I-gastrin for radioimmunoassays and receptors studies

A simple procedure has been developed for monoiodination of gastrin to a high specific radioactivity. The COOH-terminal hexadecapeptide fragment of gastrin-17 was coupled at the NH2-terminal glycine residue to iodinated 3-(4-hydroxyphenyl) propionic acid N-hydroxysuccinimide ester. The labelled hexadecapeptide was then efficiently separated from unlabelled hexapeptide and other reagents by chromatography on Sephadex G-50 superfine columns. The mean specific radioactivity was 560 microCi/nmol (n = 5). The tracer was stable and useful for three to four months. The present NH2-terminal monoiodination procedure is a valuable supplement to our previous technique for monoiodination of gastrin at tyrosine-12, in that the NH2-terminal labelled gastrin is well bound also to antisera and receptors specific for the tyrosine containing sequence of gastrin. In addition the present procedure requires only simple gel filtration instead of ion-exchange chromatography in order to achieve adequate separation of labelled from unlabelled gastrin.