the intermediate enzyme in the metabolism of catecholamines from the dietary amino acid tyrosine. Tyrosine is transformed to L-dopa by tyrosine hydroxylase. L-dopa is in turn converted to dopamine by dopa decarboxylase, which also transforms a number of other aromatic amino acids. Dopamine is the final product in dopaminergic neurons; in adrenergic neurons, dopamine is transformed by the enzyme dopamine beta-hydroxylase to norepinephrine and subsequently—in specialized cells in the adrenal medulla and other sites, via the action of the enzyme phenylethanolamine N-methyltransferase—to epinephrine. Also called aromaticL-amino acid decarboxylase.