Physical and chemical studies of a limited reaction of iodine with proteins.

Although iodine is generally regarded as having two main effects on proteins, oxidation of sulfhydryl groups and substitution on the conjugated aromatic rings of tyrosine and histidine, conditions have been known for many years that apparently permitted only the oxidative reactions to occur (l-3). Investigations carried out under these conditions have generally been interpreted as suggesting oxidation to the level of disulfide, though sulfenyl iodide and higher states of oxidation of sulfur have been reported (4, 5). The structural implications of this postulated creation of new disulfide bonds in proteins led us to investigate the effects of treatment with small quantities of iodine upon the physical behavior of ovalbumin, &lactoglobulin, and serum albumin. It would appear now that sulfenyl iodide formation is more common than previously supposed, that intermolecular disulfide formation does not occur with these proteins, and that intramolecular disulfide formation is not a major factor, though it cannot be completely excluded. Stoichiometry of the reaction as it relates to iodine-iodide-protein-substituted iodine is complicated by the appreciable spontaneous hydrolysis of the sulfenyl iodide group.