Preparation of ¹²⁵I-Labelled Synthetic Human Gastrin I for Radioimmunoanalysis

Abstract

A reproducible procedure for labelling of synthetic human gastrin has been developed. An excess of hormone was iodinated with [¹²⁵I]NaI by a modification of the chloramine T method. The reaction was performed at a low concentration of chloramine T (0.6 mmol/1) and at a low level of radioactivity (200 μCi). Purification and separation of labelled from unlabelled hormone was carried out by gradient elution chromatography on an AE-41 cellulose column. Synthetic human gastrin was heterogeneous, but only one purification step was needed. The labelled preparation was found to be homogeneous and of high specific radioactivity (702 + 28 μCi/nmol, mean ± S.E.M.). The immunoreactivity was considerably improved. The tracer was stable and employable for at least three months, while gastrin labelled by conventional modifications of the chloramine T technique could be used for only three to four weeks.

Key Words:

• Gastrin
• radioimmunoassay
• radioiodination