Iodine and GPXs involved in Thyroid Hormones Biosynthesis.

<p>The serum sodium iodide is transported into the thyrocyte and then iodine is incorporated into the thyroglobulin molecule (Tg) in a reaction catalyzed by the hemoprotein thyroid peroxidase (TPO). In this reaction, H₂O₂ generated by the NADPH-dependent thyroxidase (ThOx) is required as substrate by TPO for the iodination and coupling of tyrosyl residues in Tg. Then, thyroid hormones triiodothyronine (T3) and tetraiodothyronine (T4) are released into the bloodstream. H₂O₂ used in this reaction decreases the amount of H₂O₂ that would otherwise be available for damaging oxidation reactions. Selenium-dependent glutathione peroxidase 1 (<i>GPX 1</i>) and other GPX s remove H₂O₂ from the tissues, also decreasing oxidative damage. (Modified from: J. Köhrle <i>et al</i>. Selenium, the thyroid, and the endocrine system. Endocrine Reviews, December 2005, 26(7):944–984; Lyn Patrick, ND. Iodine: deficiency and therapeutic considerations. Alternative Medicine Review, 2008, 13(2):116–127).