Changes in the secondary structure of proteins labeled with 125I. CD spectroscopy and enzymatic activity studies

Bovine serum albumin (BSA) and lysozyme (LSZ) were radiolabeled with 125I. Three different methods for protein iodination with 125I were optimized. Parameters like incubation time and ratio of oxidizing agent and amount of protein were established. During protein iodination with 125I, structural damages caused by the introduction of iodine into the protein may occur. These damages depend on the oxidizing agent used and may lead to considerable changes in the protein structure and, hence, their biological activity. Changes in secondary structure of LSZ and BSA were examined by circular dichroism (CD). Enzymatic activity tests were performed with lysozyme to check its biological activity. The Iodo Bead was found the best oxidizing agent for protein iodination. (author)