The Catecholamine Biosynthesis pathway depicts the synthesis of the the catecholamine neurotransmitters. Catecholamines are sympathomimetic hormones that are released by the adrenal glands in response to stress. They are part of the sympathetic nervous system. They are called catecholamines because they contain a catechol group, and are derived from the amino acid tyrosine. The most abundant catecholamines are epinephrine (adrenaline), norepinephrine (noradrenaline) and dopamine, all of which are produced from phenylalanine and tyrosine. They are synthesized in catecholaminergic neurons by four enzymes, beginning with tyrosine hydroxylase (TH), which generates L-DOPA from tyrosine. The L-DOPA is then converted to dopamine via aromatic L-amino acid decarboxylase (AADC), which is then converted to norepinephrine via dopamine beta-hydroxylase (DBH); and finally to epinephrine via phenylethanolamine N-methyltransferase (PNMT).