Dopamine β-hydroxylase [DBH; dopamine β-monooxygenase; EC l.14.17.1 3, 4-dihydroxyphenylethylamine; ascorbate: oxygen oxidoreductase (hydroxylation)] is a copper-containing monooxygenase that catalyzes hydroxylation of a phenylethylamine (mainly dopamine in vivo) at the β-C of the side chain to a phenylethanolamine [noradrenaline (NA) from dopamine], using molecular oxygen and ascorbic acid as an electron donor. DBH localizes in noradrenergic and adrenergic neurons of the brain, in noradrenergic neurons of peripheral sympathetic nerves, and in NA and adrenaline (A) cells of the adrenal medulla, and synthesizes NA and A, which are important neurotransmitters and hormones (Nagatsu, 1973 ) (Fig. 1 ).