Human Phenol Sulfotransferase: Correlation of Brain and Platelet Activities

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Abstract
Phenol sulfotransferase (PST; EC 2.8.2.1) catalyzes the sulfate conjugation of phenolic and catechol neurotransmitters and drugs. The human blood platelet has been the most thoroughly studied source of PST because of the possibility that the regulation of the enzyme in this easily accessible tissue might reflect the regulation of PST in the CNS. The human brain and platelet contain at least two forms of PST, forms designated as thermostable (TS) and thermolabile (TL) PST. TS PST catalyzes the sulfate conjugation of micromolar concentrations of phenol and p‐nitrophenol and TL PST catalyzes the sulfate conjugation of dopamine and other monoamines. This study was performed to determine whether individual variations in the activities of human platelet TS and TL PST reflect individual variations in cerebral cortical PST activities. PST activities were measured in platelets and in cerebral cortical tissue obtained from 15 patients with epilepsy during clinically indicated neurosurgery. There was a highly significant correlation between the activities of the TS form of PST in cerebral cortex and platelets of these patients (r = 0.940, p < 0.001), but there was not a significant correlation between activities of the TL form of PST in the two tissues (r = 0.396, p > 0.14). In addition to variations in the level of enzyme activity, there are also wide individual variations in the thermal stability of platelet TS PST. When the thermal stabilities of platelet and cerebral cortical TS PST were compared in these same patients, the slopes calculated from semilogarithmic plots of thermal inactivation data were strongly correlated for cerebral cortex and platelet samples (r = 0.9598, p < 0.001). Therefore, individual variations in both basal enzyme activity and the thermal stability of platelet TS PST activities directly reflect individual variations in cerebral cortical TS PST activities and thermal stability in patients with epilepsy who were undergoing neurosurgery.