A new solid-state reagent to iodinate proteins: I. Conditions for the efficient labeling of antiserum

A new solid-state reagent for iodinating polypeptides and proteins was used to radiolabel antiporcine insulin antiserum. Reaction conditions of pH, temperature, buffer, reactant concentration, and the type of reaction vessel were optimized to achieve almost quantitative incorporation of radioiodide (99%), good recovery of protein (92%), and a moderate specific activity (9.9 μCi/μg of antiserum). A second set of conditions was found to produce antiserum of high specific activity (161 μCi/μg) which retained its immunological ability to recognize insulin. The nature of the actual iodinating species and the effects on the reaction of sodium azide, detergents, and chaotropic reagents such as urea and high salt were investigated.