Enzymatic sulfation of steroids. XI. The extensive purification and some properties of hepatic sulfotransferase III from female rats.

Our earlier studies showed that livers from female rats contained three glucocorticoid sulfating enzymes we named sulfotransferases I, II, and III, (STI, STII, and STIII, respectively). In this report STIII from female Charles River CD rats was purified 1010- to 1300-fold compared with liver homogenates. The most highly purified STIII fraction electrophoresed as a single protein band. The molecular weight of STIII was 68 300 +/- 4900. Its pH optimum for cortisol sulfation was pH 6.0 +/- 0.1. However, it was routinely assayed at pH 6.8 for reasons enumerated in the text. Cortisol sulfation by STIII proceeded by either an ordered sequential mechanism or by an Iso Theorell-Chance mechanism at pH 6.8. The Km's for cortisol and the reaction coenzyme, 3'-phosphoadenosine-5'-phosphosulfate were 6.48 +/- 0.78 and 6.78 +/- 1.26 microM, respectively. Comparison of the ability of the enzyme to sulfate 40 microM cortisol, estradiol-17 beta, testosterone, deoxycorticosterone, and dehydroepiandrosterone, showed that the glucocorticoid was sulfated preferentially. Interestingly, its cortisol sulfotransferase activity was inhibited by a number of steroids. p-Hydroxymercuribenzoate inhibition studies indicated the presence of essential sulfhydryl groups in STIII. The enzyme was activated by divalent Ba, Ca, Co, Cr, Mg, Mn, and Ni salts. It was inactivated by Zn2+ and Cd2+ salts. The text compares STIII from female rats with other steroid sulfotransferases including the major glucocorticoid sulfotransferase from male rats.