Tyrosine is a non-essential amino acid. It is synthesized from essential phenylalanine. Food products such as chocolate, milk and eggs contain phenylalanine. In blood, tyrosine circulates as a part of thyreoglobuline(protein carrier). Triiodothyronine(T3) and Thyroxine(T4) hormones of thyroid gland are synthesized by reaction of tyreoglobuline and iodine with tyrosine. Catecholamines such as adrenaline, noradrenaline and dopamine are also tyrosine derivatives.