T4 is transported in blood, with 99.95% of the secreted T4 being protein bound, principally to thyroxine-binding globulin (TBG), and, to a lesser extent, to transthyretin and serum albumin. T4 is involved in controlling the rate of metabolic processes in the body and influencing physical development.
Note: Thyroxine is a prohormone and a reservoir for the active thyroid hormone triiodothyronine (T3). T4 is converted in the tissues by deiodinases to T3. The "D" isomer is called "Dextrothyroxine"[1] and is used as a lipid modifying agent.[2] The half-life of thyroxine once released into the blood circulatory system is about 1 week.
The hormone was synthesised in 1927 by British chemists Charles Robert Harington and George Barger.