Chemical Biology of Thyroid Hormones

Thyroid hormones (THs) are synthesized in thyroid follicular cells and secreted by the thyroid gland. These hormones play crucial roles in regulating the body metabolism and temperature, heart rate, neuronal growth, cardiovascular, renal and brain functions. Thyroid gland mainly produces the iodine-containing prohormone L-thyroxine (T4), which undergoes monodeiodination or 5’-deiodination by the selenium- containing iodothyronine deiodinases (DIOs) to generate the biologically active hormone T3. In this general review, the chemical biology aspects of thyroid hormone actions in various organs, biochemical synthesis of T4 in thyroid gland, the role of iodine, thyroglobulin, and thyroid peroxidase in the chemical pathways of hormone synthesis, the transport of hormones by various transport proteins in the blood stream, and various metabolic pathways. The regioselective deiodination of T4 by three isoforms of DIOs to produce active and inactive metabolites and the receptor binding of thyroid hormones are also discussed.