Description phenylalanine is an essential amino acid and the precursor the amino acid tyrosine like tyrosine it is the precursor of catecholamines which consist of dopamine epinephrine otherwise known as adrenalin and tyramine it is metabolised primarily in the liver normal metabolism of phenylalanine requires iron niacin vitamin b 6 copper and vitamin c phenylalanine is the starting material of several catecholamines and also of ubiquinone co enzyme q10 it also plays a role in lea