Sulfate conjugation is an important pathway in the metabolism of drugs, xenobiotic compounds, neurotransmitters and hormones. The experiments proposed in this application are designed to enhance our understanding of biological mechanisms responsible for individual variations in sulfation in humans. Special emphasis is placed on the role of inheritance i.e., on pharmacogenetics. Phenol sulfotransferase (PST, E.C. 2.8.2.1) is the most important of the drug metabolizing enzymes which catalyzes sulfate conjugation. All human tissues that have been studied contain at least two forms of PST which differ in their substrate specificities, inhibitor sensitivities, physical properties and regulation. These two forms of PST differ in their thermal stability and will be referred to subsequently as the thermostable (TS) and thermolabile (TL) forms of the enzyme. We have found that both forms of PST in the human platelet are regulated by genetic polymorphisms, and that genetically controlled levels of activity and physical properties of TS PST in the platelet reflect those of TS PST in other human tissues. We now propose to use photoaffinity labeling of the active site and amino acid sequencing of purified TS and TL PST to study the molecular basis for the genetic control of this enzyme in human tissue. Our recent discovery that another important sulfate conjugating activity, estrogen sulfotransferase (EST, E.C. 2.8.2.4), is found in the human platelet will make it possible to determine whether inheritance also plays a role in the regulation of EST activity levels or physical properties in the platelet as it does for PST. In addition, it will be determined whether the biochemical properties and regulation of EST in an easily accessible human tissue, the platelet, are similar to and correlated with those of EST in the human liver. EST will be purified from both human platelet and liver, and photoaffinity labeling and amino acid sequencing will be performed to study the possible relationship of EST to PST. The results of these studies will enhance our understanding of biological mechanisms responsible for individual variations in the sulfate conjugation of drugs, xenobiotics, neurotransmitters and hormones in humans.
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