Localization and characterization of phenol sulfotransferase in human platelets

Phenol sulfotransferase was localized as a soluble enzyme in platelets from human blood. The enzyme was found to esterify a variety of endogenous phenolic biogenic amines including tyramine, dopamine, norepinephrine and 5-hydroxytryptamine as well as phenol. Of the substrates tested dopamine was found to be most rapidly conjugated when present at a concentration of 30 μM while tyramine was found to be the best substrate at a concentration of 100 μM. The Km value for tyramine was 59 μM and tyramine concentrations of 400 μM or greater resulted in apparent substrate inhibition. The possible clinical implications of of these findings are discussed.