Endocrine steroid sulfotransferases: Steroid alcohol sulfotransferase from human breast carcinoma cell line MCF-7

Abstract

Steroid alcohol sulfotransferase (SAS) has been isolated from the cytosol of a human breast carcinoma cell line, MCF-7. This enzyme from Sephadex G-200 chromatography displayed a mol. wt of 118 KDa. The conditions for optimal enzymic activity of SAS were determined to be 20 min incubations at 45°C in 0.2 M Tris buffer (pH 7.5) containing 0.06 M Mg 2+. Chromatofocusing chromatography also yielded a single peak of SAS with a pI of 5.8. Results from the incubations of a series of androstane analogues revealed that SAS required a 3β-hydroxyl on a steroid with the trans bridge between the A and B rings. Neither the 3β-allylic hydroxyl group nor the A-ring phenolic 3-hydroxyl accepted the sulfate group from 3'-phosphoadenosine-5'-phosphosulfate. d-ring β-hydroxyl groups were tolerated by the enzyme, however, α-hydroxyl groups on the d-ring appeared to interfere with the reaction. Sulfurylation of steroids by SAS was related inversely to the sum of the displacements of the 3-hydroxyl plus that of the 17-hydroxyl groups relative to the plane of symmetry of the dehydroepiandrosterone nucleus. This enzyme was also capable of sulfurylating short chain aliphatic alcohols, although at greatly reduced rates. 3β-Chloro-5-androstene-17-one and 2-nitroestradiol.17β proved to be the best inhibitors of SAS.