Maintenance of biological activity of pertussis toxin radioiodinated while bound to fetuin-agarose

We developed a method to produce radioiodinated pertussis toxin (PT) which was active in the goose erythrocyte agglutination and CHO cell assay systems. The procedure used fetuin coupled to agarose to prevent inactivation of the toxin during the iodination reaction. Analysis of the labeled PT by affinity chromatography on fetuin-agarose and wheat germ agglutinin-agarose and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that there were minimal amounts of labeled fetuin or other contaminants in the labeled PT preparations. All five of the subunits of the toxin appeared to be labeled by the procedure. The labeling method will facilitate further investigations into the nature of the interaction and activity of PT in host tissues.