Procedures were examined for labeling immune globulins with radioactive iodine using chloramine-T as the oxidizing agent. The chloramine-T method was critically evaluated to establish the optimal conditions for preparing iodinated globulins with high specific radioactivities without impairing their immunospecificities for use in in vitro radioimmunoassays. The results showed that the use of 100 μg of chloramine-T per ml, 500 to 1,000 μCi of Na 125I per mg of protein, and a 10-min oxidation reaction time produced globulins of both high specific radioactivities and immunospecificities. Criteria were established for evaluating and determining optimal concentrations of iodine-labeled globulin for use in radioimmunoassays. The results of this investigation indicated that the amount of labeled indicator globulin used in radioimmunoassays should be based upon protein concentration rather than radioactivity.
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