Enzymatic sulfation of steroids. V. Partial purification and some properties of sulfotransferase III, the major glucocorticoid sulfotransferase of liver cytosols from male rats

Abstract

This manuscript describes purification of sulfotransferase III (STIII), the major hepatic glucocorticoid sulfontransferase of male rats, 77.8 +/- 16 fold from cytosol. This represents a probable 250--345 fold enrichment, compared with homogenates. Purified STIII has a molecular weight of 61 500 +/- 2500 from Sephadex G-100 chromatography. It is markedly activated by 5 mM divalent Ba, Ca, Co, Cr, Mg, Mn, and Ni salts; inhibited stronlgy by 5 mM divalent Zn and Cd; and unaffected by 8 mM ADP, ATP, and AMP. Comparison of the ability of purified STIII to sulfate equimolar cortisol, estradiol-17beta, testosterone, and dehydroepiandrosterone suggests that the enzyme may sulfate glucocorticoid preferentially. However, its cortisol sulfotransferase activity is inhibited by a variety of steroids. Of these, dehydroepiandrosterone, dexamethasone, and progesterone were tested extensively. They were found to be competitive inhibitors. STIII has a sharp pH optimum at pH 6.0 +/- 0.1. However, it is routinely assayed at pH 6.8, as explained in the text. It exhibits a sequential mechanism and Km values of 6.82 +/- 1.2 and 6.28 +/- 0.64 micron for cortisol and 3'-phosphoadenosine-5'-phosphosulfate, respectively. It also possesses essential sulfhydryl groups, as shown by p-hydroxymercuribenzoate inhibition studies.