Effect of Fluoride on the Biogenesis of Thyroid Hormones

Abstract

THE biogenesis of thyroid hormones occurs in several successive stages. Accumulation of iodine in the thyroid may be considered as the first of these, while the second is represented by the binding of ‘active iodine’ on the tyrosine radical, 3-monoiodo-tyrosine being formed in the process. It would seem that a further enzymatic system¹ is responsible for the production of 3 : 5-diiodotyrosine, and a fourth phase in this biogenesis consists in the synthesis of iodinated thyronines into thyroxine, 3 : 5 : 3′-triiodothyronine, 3 : 3′ : 5′-triiodothyronine and 3 : 3′-diiodothyronine. In addition to these biosynthetic enzyme systems intervening in the thyroid, it is necessary to mention also the deiodinating enzyme, acting selectively on iodinated tyrosines and the proteolytic enzymes which liberate amino-acids from the thyroglobulin.