Tritium (3H) radiolabeling of protein A and antibody to high specific activity: application to cell surface antigen radioimmunoassays.

Staphylococcal protein A and several different immunoglobulins have been radiolabeled to high specific activities (greater than 10(6) cpm/microgram) by reductive methylation with tritiated (3H) sodium borohydride. The proteins retain excellent functional and antigenic properties. The utility of these reagents in a variety of assays for cell surface antigens is illustrated. The results indicate that this radiolabeling procedure may become the method of choice for many cell surface and solution immunoassays.