Liberation of Hydrogen Ions and pH Dependence of a Protein-Iodine Reaction

In earlier communications (1, 2), we described a specific reaction of iodine with the sulfhydryl groups of proteins, and presented evidence that the initial product of this reaction is the sulfenyl iodide group. Part of this evidence involved spectrophotometric determination of the stoichiometry of the iodineprotein reaction. In this communication, we describe the measurement of a second product of this reaction, hydrogen ion, since the ratio of iodine consumed to hydrogen ion liberated is characteristic of the level of oxidation of iodine in this system. The establishment of this ratio has provided a further confirmation of the formation of stable sulfenyl iodide groups in native proteins.