<prompt> Which of the following is the precursor for adrenaline and thyroxine synthesis?PhenylalanineTyrosineTryptophanNone of the above  <response>: Harper 267, 446Tyrosine is the precursor for triiodothyronine and thyroxine. It is also an immediate precursor for the catecholamines adrenaline and tyrosine hydroxylase is the rate limiting enzyme in the catecholamine biosynthesis. 