Partial purification and some properties of rat liver sulfotransferase I,a glucocorticoid sulfotransferase usually restricted to female rats

Three rat liver enzymes, sulfotransferases I, II, and III, sulfate glucocorticoids. This report describes the purification of sulfotransferase I, the glucocorticoid sulfotransferase usually restricted to females, 227 ± 63-fold from cytosol. As shown, this represents a probable 1000- to 1250-fold enrichment compared to liver homogenates. Highly purified sulfotransferase I exhibits a molecular weight of approximately 156,000, determined by sedimentation velocity experiments. Its pH optimum is pH 6.0 ± 0.1. However, its properties are routinely measured at pH 6.8 for reasons enumerated in the text. At this pH it exhibits a sequential mechanism for cortisol sulfation. Its K_m values for cortisol and its coenzyme, 3′-phosphoadenosine-5′-phosphosulfate, are 7.09 ± 0.65 and 10.6 ±1.1 μm, respectively. Sulfotransferase I also appears to contain essential sulfhydryl groups, shown by p-hydroxymercuribenzoate inhibition studies. Furthermore, it is activated by divalent Co, Cr, Mg, or Mn and inhibited by 100 μm Cd²⁺ or 50 μm Zn²⁺. Comparison of the ability of purified sulfotransferase I to sulfate 40 μm cortisol, dehydroepiandrosterone, deoxycorticosterone, estradiol-17β, and testosterone showed that sulfotransferase I is not as specific a glucocorticoid sulfotransferase as is sulfotransferase III (described earlier). Sulfotransferase I was inhibited strongly by a variety of steroids and diethylstilbestrol at 1.0 μm concentrations. Extensive comparisons of the properties of sulfotransferases I and III and their potential significance are made throughout the text.