Toxicity and Immunochemical Properties of I131 Trace Labeled Diphtheria Toxin

Diphtheria toxin was labeled with I131 by methods currently in use. Trace iodination was found to induce changes in the properties of diphtheria toxin. These changes were due to at least two factors: introduction of large quantities of iodine into the toxin or to the method by which toxin was labeled. Methods of iodination which exposed the toxin to extremes of pH, either acid or alkaline, were found to be as significant as overiodination in altering diphtheria toxin. Loss of toxicity for guinea pigs was found to be the most sensitive index for studying the effects of trace iodination and flocculation the least sensitive. The use of the tri-iodide method at pH 7.5 with about one mole of iodine per mole of toxin was effective in labeling diphtheria toxin with I131 with no significant loss or alteration in toxicity or immunochemical behavior.