Question: what is the nature of thyroid hormone?
Answer: Thyroid hormones are derivatives of the the amino acid tyrosine bound covalently to iodine. The two principal thyroid hormones are: thyroxine (also known as T4 or L-3,5,3',5'-tetraiodothyronine) triiodothyronine (T3 or L-3,5,3'-triiodothyronine)