DIRECT RADIOIODINATION OF ESTRADIOL FOR A SENSITIVE RADIOIMMUNOASSAY

17 β-estradiol (E2) was iodinated with the chloramine-T method. The125I-labelled material was purified with thin-layer chromatography. The major fraction was applied to a radioimmunoassay with an antiserum against estradiol-6-(O-carboxymethyl)oxime-BSA. The sensitivity of the assay was comparable to assays with 3H-E2 or125I-nistamine-E2 as tracers. The working antiserum dilution (1:1 000 000) was the same with125I-E2 and3H-E2 but lower than that with125I-histamine-E2. The results indicate that iodination of the A-ring of estrogens will not cause significant reduction of the immunoreactivity when combined with an antiserum to a B-ring conjugate. © 1979 by The Endocrine Society.