A STUDY OF THE CHARACTERISTICS OF THYROIDAL AND EXTRATHYROIDAL ENZYME SYSTEMS WHICH CATALYZE THE ORGANIC BINDING OF IODINE

Abstract

An iodide oxidizing enzyme system has been discover in extracts of thyroid and certain salivary gland tissues which promotes the formation of elemental iodine. This enzyme system appears to function as a part of the previously reported tyrosine iodinaso system which catalyzes the formation of monoiodotyrosine, a precursor of thyroxine, from tyrosine. A mitochondrial enzyme system, which iodinates tyrosine residues in protein chains and which was previously reported to occur solely in the thyroid gland, has been detected in a number of extrathyroidal centers. Similarities in behaviour towards substrates and the co-existence of the mitochondrial and tyrosine iodinase systems in tissues may indicate that the systems are basically the same. The tyrosine iodinase system has boon used to distinguish between two mechanisms developed to explain the anti-thyroid action of excess iodide ion.