Formation of Thyroid Hormones

Abstract

Publisher Summary This chapter discusses the formation of thyroid hormones. The metabolic pathway that allows the synthesis of thyroid hormones from inorganic iodide has been extensively documented at the physiological level, the investigations being greatly facilitated by the use of the iodine isotopes. However, only the phenomenology of this process can be easily studied in these conditions, not the mechanism. In vivo the situation is complicated by the asymmetry of the thyroid cell (with its apical and basal membranes); by the morphology of the thyroid vesicles and their variability in size and in activity; by large variations in iodide fluxes, which depend not only on changes in dietary intake but also on the regulatory status of the gland; and by the secretion process, which seems to remove preferentially from the colloid either the newly iodinated thyroglobulin or older molecules depending on the physiological situation, etc. In vitro, with the isolated and purified enzyme, these difficulties are eliminated: the system that can be used consists only of a mixture of the enzyme, thyroid peroxidase, H2O2, iodide, and thyroglobulin.