Enzymic sulfation of bile salts. Partial purification and characterization of an enzyme from the liver of the shark Heterodontus portusjacksoni that catalyses the sulfation of the shark bile steroid 5β-scymnol

Abstract

An enzyme system which catalyses the transfer of the sulfate group from 3′-phosphoadenosine-5′-phosphosulfate to the bile steroid 5β-scymnol has been isolated and characterized from the liver of the shark Heterodontus portusjacksoni (Meyer 1793). The enzyme is present in the cytosol fraction of liver cells. It was partially purified by hydroxylapatite chromatography, molecular sizing by G100-Sephadex and isoelectrofocusing electrophoresis. The apparent K m value for 3′-phosphoadenosine-5′-phosphosulfate was 4μM and that for 5β-scymnol, 14μM. The enzyme activity is inhibited by iodoacetate and p-chloromercuribenzoate indicating the possible requirement of a sulfhydryl group for activity. The molecular weight of the enzyme was estimated to be 40 kDa by gel filtration. This was verified by running the partially purified material on a native gel and electrophoretically separating two major bands corresponding to molecular weights of 40 and 45 kDa, respectively. Isoelectric focusing of the purified material resulted in two major bands with pI values of 5.0 and 5.85. Enzymatic activity was found to be optimal at a pH of 6.5 with little activity recorded at pH 5.0 and 8.0.