The molecular heterogeneity and instability of radioiodinated human chorionic gonadotrophin.

Gel chromatographic studies on radioiodinated HCG have shown that a polymer and fragmented materials are associated with the radiolabelled product which interfere in the RIA of HCG in serum. Scatchard plots of experimental data indicated that the polymer material (fraction I) has two species of antigenic determinants that recognize two species of binding sites on the anti-HCG-beta. The use of purified 125I-HCG (gel chromatographic fraction II) for radioligand improved the reliability of the RIA. It was further demonstrated that a labelled preparation of HCG could be used for RIA tests for periods of five weeks or longer provided that chromatographic purification was carried out immediately prior to the assay.