5 beta-Scymnol sulfotransferase isolated from the tissues of an Australianshark species

The enzyme system involved in the sulfation of 5 beta-scymnol [(24R)-5 beta -cholestane-3 alpha,7 alpha,12 alpha,24,26,27-hexol] has been investigated in the shark species Heterodontus portusjacksoni. The liver enzyme was part ially purified by column chromatography and chemically characterized. In it s partially purified form the enzyme showed typical Michaelis-Menten kineti cs for 5 beta-scymnol and the sulfonate donor 3'-phosphoadenosine 5'-phosph osulfate (PAPS) with an apparent K-m of 3.04 mu M for 5 beta-scymnol and 4. 35 mu M for PAPS. The reaction product adenosine-3',5'-diphosphate and the substrates tested all inhibited the liver enzyme at concentrations above 10 mu M. Substrate specificity of the enzyme was investigated using 5 alpha-c yprinol, dehydroepiandrosterone, 17 beta-estradiol and testosterone. Only 5 alpha-cyprinol was as efficiently sulfated as 5 beta-scymnol and suggests that the presence of the chiral alcohol group at C-24 is not essential for binding of the C-27 bile steroids in the active site of the enzyme. A surve y of tissue cytosolic fractions revealed that sterol sulfotransferase activ ity was present in the liver, kidney and testis; however, it was absent fro m the spleen, pancreas, brain, duodenum, heart and ovary. (C) 1998 Elsevier Science Inc. All rights reserved.