Dopamine-4-O-sulfate: a possible precursor of free norepinephrine.

Incubation of dopamine-4-O-sulfate with purified bovine dopamine-beta-hydroxylase led to the formation of free norepinephrine. The production of free norepinephrine was completely inhibited in the presence of 5.6 mM of fusaric acid, an inhibitor of dopamine-beta-hydroxylase. No sulfatase activity was detected in the incubation medium. The reaction of dopamine-4-O-sulfate with dopamine-beta-hydroxylase followed Michaelis-Menten kinetics, showing an apparent Km of 2.6 mM.