Radioiodination of Enterotoxin from Clostridium perfringens Type A using Chloramine T

Procedures were examined for labelling enterotoxin isolated from Clostridium perfringens type A. with 125 I using chloramine T as the oxidizing agent. The iodination method was evaluated critically to establish the optimal conditions for the preparation of iodinated enterotoxin with a high specific radioactivity and without impairing the immunospecificity and biological activity. The use of 250 μg/ml of chloramine T in the reaction mixture. 500–1000 μCi of Na 125 I/10 μg of enterotoxin and a reaction time of 40 s at pH 7–0 produced 125 I‐enterotoxin of both high specific radioactivity and immunospecificity which retained its biological activity. No damage or aggregate formation due to the iodination process was observed. Enterotoxin labelled with high specific activity (135 μCi μg) showed extensive dissociation of 125 I when stored at 4°C and—20°C. In contrast, toxin labelled with low specific activity (7 μgCi/μg) was stable for as long as two months. The immunoreactivity of all labelled preparations was essentially unchanged after storage for one month.