Enzymatic iodination of salivary proteins by the 125I-lactoperoxidase system.

Purified milk lactoperoxidase and endogenous human salivary peroxidase were used to label the proteins of whole mouth saliva with [125I]iodide. The proteins were then analyzed by isoelectric focusing or they were subjected to one-dimensional polyacrylamide gel electrophoresis at pH 8.4. The radioactivity of the resolved protein fractions was determined. There were three to four major and four to five minor areas of radioactivity which were carried together with more or less distinctive protein fractions. Amylase and albumin were shown to be the most effective in binding [125I]iodide. No significant differences were observed in the iodination patterns of salivary proteins iodinated in the presence of endogenous saliva peroxidase and those iodinated in the presence of added milk lactoperoxidase. Hydrogen peroxide was necessary for iodination to take place. The significance of iodoproteins and the role of salivary peroxidases in the nonthyroidal metabolism of iodine are discussed.