The Role of Intermediary Carbohydrate Metabolism in Regulating Organic Iodinations in the Thyroid Gland*

As pointed out in recent reviews (1, 2), the synthesis of hormonally active materials by the thyroid gland proceeds via a sequence of seemingly discrete reactions.These may be categorized as follows: concentration of inorganic iodide from the extracellular fluid, oxidation and organic binding of iodine to yield iodotyrosines, and coupling of iodotyrosines to form the hormonally active iodothyronines.The latter two groups of reactions occur within the matrix of the thyroglobulin molecule, a large molecular protein for whose synthesis and storage the thyroid gland is especially adapted.It seems clear that ultimately the energy for these synthetic processes, as well as for the main- tenance of glandular architecture, must derive from metabolic sources.However, little is known of how the energy released during intermediary metabolism is imparted to those reactions involved in hormonal biosynthesis.Previous studies have indicated that the iodide-concentrating function of the thyroid is dependent on oxidative processes leading to the formation of high energy phosphate bonds (3, 4).The present studies were under- taken to determine whether a comparable link to metabolic events could be delineated in the case of the next stage in hormonal synthesis, the oxi- dation of iodide and formation of monoiodotyrosine.From the results obtained, a metabolic sequence is postulated whereby the oxidation of * This investigation was supported in part by Re- search Grant no.A-267 from the National Institute of Arthritis and Metabolic Diseases, Bethesda, Md., and in part by the Medical Research and Development Board, Office of the Surgeon General, Department of the Army, under Contract no.