Enzymatic sulfation of bile salts. II. Studies on bile salt sulfotranferase from rat kidney

Abstract

An enzyme system which catalyzes the transfer of the sulfate group from 3′-phosphoadenosine-5′-phosphosulfate to bile salts has been isolated and characterized from rat kidney. The enzyme is present in the cytosol fraction of kidney cells. It was purified by DEAE-Sephadex A-50, agarose-hexane-adenosine 3′,5′-diphosphate affinity chromatography and isoelectrofocusing electrophoresis. The apparent K m values of the enzyme are 2 · 10 −6 M for 3′-phosphoadenosine-5′-phosphosulfate, and 4 · 10 −5 M for taurolithocholate. Sulfation occurred with conjugated as well as with unconjugated bile salts. The enzyme reacts with both primary bile salts (cholate, chenodeoxycholate and their conjugates), and secondary bile salts (lithocholate and its conjugates). The rates of reaction in decreasing order are monohydroxylated > dihydroxylated > trihydroxylated and glycoconjugates > tauroconjugates > unconjugates. The enzyme activity is inhibited by p-chloromercuri benzoate and iodoacetate indicating the possible requirement of a sulfydryl group for activity. A molecular weight of 80 000 was estimated by gel filtration techniques which is significantly smaller than the liver enzyme (130 000). The purified enzyme does not react with estrone or dihydroepiandrosterone.