Studies of the Biosynthesis of Thyroxine. I. Purification and Properties of a Particulate Iodide Peroxidase from Thyroid Tissue.

Previously, a number of workers have described preparations of thyroid tissue which catalyze the iodination of free or proteinbound tyrosine (l-7). It was demonstrated that the enzymatic activity was mitochondrial in location, and depending upon the method of preparation or assay, various metals and cofactors were implicated in the reaction. Serif and Kirkwood (1, 2) found that addition of certain metals increased activity, whereas Chaikoff, Taurog, Potter, and Tong (3, 4) reported that flavin mononucleotide and manganese ions stimulated enzymatic catalysis. Alexander (5) suggested that the oxidation of iodide is a peroxidation and found that the addition of hematin to preparations of thyroid tissue stimulated activity (6). In each of these studies, the activity of the enzymes was followed by measuring the production of iodinated tyrosines with radioactive iodine. The present paper describes the purification and properties of a highly active particulate enzyme system isolated from beef thyroid tissue which catalyzes the peroxidation of iodide to iodine.