This report describes a method of radiodination and use of synthetic human (15Leu)gastrin in radioimmunoassay for synthetic or naturally occurring human gastrin. Specific activity of the [Y]monoiodo( 15Leu)gastrin was 45% higher than that obtained with conventional gastrin. Radioimmunoassay using a radiolabeled (15-Leu)gastrin trace was reliable between lo-i2 and 10e9 molar concentrations of synthetic human or naturally occurring gastrin.
Synthetic human (15Leu)gastrin
l-17-1, referred to as SH (15Leu)gastrin, differs from synthetic human gastrin l-17-1, referred to as SH gastrin, by the replacement of the methionine in position 15 by a leucine residue. SH (15Leu)gastrin has been shown to be at least as effective as SH gastrin in binding to a specific gastrin receptor (1) and in stimulating acid secretion (2). Since the radioiodination of the SH gastrin molecule with chloramine-T may result in a change in the antigenicity of the molecule by oxidation at the methionine residue (3), there is some theoretical advantage to radiolabeling SH (15-Leu)gastrin rather than SH gastrin. In addition there is a practical advantage to using radiolabeled SH (15-Leu)gastrin trace for radioimmunoassays of gastrin: it is less expensive and easier to obtain.3 METHODS AND MATERIALS Hormones. SH (15-Leu)gastrin was purchased from Research Plus Labs, N. J., and SH gastrin was purchased from Imperial Chemical Industries, England.
Antisera. Two antisera produced in rabbits were used. Antiserum 1802,