Effect of the insulin iodination on the reactivity of the inter-chain disulphide bonds towards sodium sulphite

Abstract

Insulin iodination interferes with the ability of the interchain S-S bonds to react with sulfite at pH7. In insulin samples containing more than 5 iodine atoms/monomer unit, only one S.S bond/molecule reacts. The effect must be related to the substitution of the iodine into the tryosyl groups, which probably causes a conformational rearrangement resulting in a steric hindrance of one of the interchain S-S bonds. The effect is removed by increasing the pH or by adding urea (8 [image]) to the reaction mixture. The unreactivity of the S.S bond and the biological inactivation occur at the same "critical" iodination level, suggesting that a same primary alteration of the molecule is responsible for both the effects.