Labeling of proteins with 125I and experimental determination of its specific activity

Abstract

The purpose of the present work consists in the standardization of the labeling technique of proteins with 125I and the control of the obtained products, principally their specific activities, in order to utilize them correctly in radioimmunoassays. The quantities of Chloramine-T and sodium metabisulphite were lowered, with regard to the original method, to 3.6 and 9.6 I.tg respectively. Under these conditions, optimal yields and radioiodinated proteins with good immunological activities were obtained. It was found that the specific activity calculated, as usual, from the yield obtained by electrophoresis, is higher than the real value. In fact, radioiodine not bound to the protein remains in the zone corresponding to the labeled protein, when analyzed by electrophoresis. This complication did not occur when chromatographic analysis was carried out.