On the chemical iodination of tyrosine with protein sulfenyl iodide and sulfenyl periodide derivatives the behaviour of thiol protein-iodine systems

Abstract

Aqueous I 2 reacted rapidly with the thiol groups of β-lactoglobulin and bovine serum albumin to form protein sulfenyl iodide derivatives. This reaction was faster than the direct iodination of protein by the reagent. When β-lactoglobulin was titrated with aqueous I 2, a well-defined equivalence point corresponding to the complete conversion of all thiol groups to their sulfenyl iodide derivative was observed. No equivalence point was observed with bovine serum albumin because the sulfenyl iodide groups produced upon titration of this protein with I 2 react rapidly with more I 2 to form sulfenyl periodide derivatives. Under the present experimental conditions protein sulfenyl iodide derivatives did not iodinate tyrosine. However, the sulfenyl periodides of both β-lactoglobulin and bovine serum albumin were able to iodinate tyrosine. This iodination was slow in comparison to direct iodination of tyrosine by I 2. A particulate preparation, isolated from bovine thyroid glands, behaved like bovine serum albumin.