Identification and partial purification of a unique phenolic steroid sulphotransferase in rat liver cytosol

Abstract

Phenolic steroid sulphotransferase activity for both oestradiol and oestrone was identified in male rat liver cytosol in the 30 000-40 000 Mr fractions on gel filtration when activity was assayed at pH 5.5 (pH optimum 5.5-6.0). Activity for oestradiol but not oestrone was found in the 60 000-70 000-Mr range when assayed at pH 8.0 (pH optimum biphasic, 5.5-6.0 and 7.0-8.0). Km for oestradiol (1.3 microM) was lower than published values for hydroxysteroid sulphotransferases (15-35 microM) and previously reported oestradiol sulphotransferases (71-85 microM). At above 2 microM-oestradiol phenolic sulphotransferase activity exhibited substrate inhibition. The phenolic steroid sulphotransferase activity was found to be distinct in chromatofocusing from organic-anion-binding and bile acid-binding proteins previously identified in this Mr range. Further purification on hydroxyapatite yielded a 44-fold enriched fraction that contained two monomeric bands, Mr 32 500 and 29 500.