Bacterial expression and kinetic characterization of the human monoamine- sulfating form of phenol sulfotransferase

The cDNA for the human monoamine-sulfating form of phenol sulfotransferase (hM-PST) was isolated from a T47D human breast carcinoma λgt10 cDNA library, and the active enzyme was expressed in Escherichia coli. Expressed hM-PST was very similar to the brain, intestinal, and platelet forms of the enzyme in its physical, immunological, and kinetic properties. The ability of hM-PST to sulfate a number of xenobiotics was examined and compared with the bacterially expressed human phenol-sulfating form of PST (hP-PST). The translation product of the T47D hM-PST cDNA was 92% identical to that of liver hP-PST. Monoamine neurotransmittors, such as epinephrine and dopamine, were maximally conjugated at lower concentrations by expressed hM-PST (2 and 20 μM, respectively) than by hP-PST (1 and 1 mM, respectively). In contrast, simple phenols-such as p-nitrophenol, acetaminophen, and α-naphthol-were maximally conjugated at lower concentrations (4 μM, 20 μM, and 0.5 μM, respectively) by hP-PST than by hM-PST(1 mM, 1.5 mM, and 50 μM, respectively). Minoxidil was sulfated at similar rates and concentrations (7 mM) by both forms of PST. None of the estrogens or related compounds, such as β-estradiol, 17α-ethinylestradiol, diethylstilbestrol, equilenin, or genistein tested as substrates were sulfated by hM-PST; however, all of these compounds were substrates for hP-PST. As with hP-PST, the hydroxysteroids dehydroepiandrosterone and cortisol were not sulfated by hM-PST. In addition, inhibition studies suggest that the amino acid differences between hM-PST and hP-PST are of adequate significance to prevent compounds with a sterol-like structure from binding the active site of hM-PST. These results indicate that there are important differences in the substrate reactivities of the two PSTs and that expression of the individual human STs in bacteria is a valuable tool for the investigation of differences in drug and xenobiotic metabolism.