Thyroxine is synthesized from:

In dopaminergic cells in the brain, tyrosine is conveed to levodopa by the enzyme tyrosine hydroxylase (TH).TH is the rate-limiting enzyme involved in the synthesis of the neurotransmitter dopamine.In the adrenal medulla, tyrosine is conveed into the catecholamine hormones norepinephrine (noradrenaline), and epinephrine.The thyroid hormones triiodothyronine (T3) and thyroxine (T4) in the colloid of the thyroid also are derived from tyrosine.