Recent Knowledge of the Biochemistry of the Thyroid Gland

Abstract

Publisher Summary This chapter reviews recent work on the three main functions of the thyroid gland—the collection of iodide from the plasma, the transformation of iodide into organically bound iodine, and the release of the hormone into the circulation. In the chapter, various factors controlling thyroid hormone synthesis are discussed and evidence is presented on the nature of the reactions involved in its synthesis, whether they are enzymic or simple chemical reactions. The influence of the pituitary gland on thyroid hormone synthesis is discussed in the chapter, with especial regard to the recent evidence of the action of thyrotropin independently on the iodide-concentrating mechanism and the organic binding of iodine. Monoiodotyrosine and di-iodotyrosine do not leave the thyroid gland after proteolytic hydrolysis of thyroglobulin but are enzymically deiodinated with the formation of iodide; this iodide is available for re-utilization in hormone synthesis. Thyroxine and triiodothyronine are released into the circulation. The part played by 3,5,3'-triiodothyronine in thyroid hormone action and the nature of thyroid hormone are discussed in the chapter. Tri-iodothyronine exhibits greater hormonal activity than thyroxine and can be shown to be derived from thyroxine in the extra-thyroidal tissues.