| Section2 = | Section3 = }} Thyroxine, or 3,5,3',5'-tetra­iodothyronine (often abbreviated as T4), a form of thyroid hormones's the major hormone secreted by the follicular cells of the thyroid gland. Thyroxine's synthesized via the iodination and covalent bonding of the phenyl portions of tyrosine residues found in an initial peptide, thyroglobulin, which's secreted into thyroid granules. These iodinated diphenyl compounds are cleaved from their peptide backbone upon being stimulated by… (More on Thyroxine)