125I-LABELLING OF ANGIOTENSIN I AND II

Abstract

ABSTRACT A simple procedure for a reproducible preparation of radioiodinated angiotensin analogues is described. The iodination is performed at a low level of radioactivity – 200 μCi per 10 μg peptide – with low concentrations of chloramine-T and sodium metabisulphite. No destruction of the peptide occurs during the iodination. The yield is high, and the only purification step needed is a separation of iodinated peptide from non-labelled peptide. This separation is performed by means of column chromatography on DEAE-Sephadex A 25. The specific activity of labelled angiotensin I or II prepared by this method was about 500 μCi/μg. The homogeneity of the radioiodinated angiotensin analogues was established by means of paper chromatography and enzymatic degradation studies, including experiments on the enzymatic conversion of 125I-angiotensin I to 125I-angiotensin II. Radiochromatograms obtained after storage for various periods showed perfect stability of the labelled compounds. Immunological characteristics, as evaluated by standard displacement curves with selected antisera and maximal binding to excess antibody, were reproducible from batch to batch.