The
major form of thyroid hormone in the blood is thyroxine (T4, see left).
This prohormone is converted to the active T3 within cells by
deiodinases.
Thyroxine (3,5,3',5'-tetraiodothyronine) is produced by follicular
cells of the thyroid gland by attaching four iodine atoms to the ring
structures of tyrosine molecules
