3alpha hydroxysteroid reductase

Rat Y' bile acid binders (33 kD) have been previously recognized as cytosolic bile acid binding proteins (Sugiyama, Y., T. Yamada, and N. Kaplowitz, 1983, J. Biol. Chem., 258:3602-3607). We have now determined that these Y' binders are 3 alpha-hydroxysteroid dehydrogenases (3 alpha-HSD), bile acid-metabolizing enzymes. 3 alpha-HSD activity copurified with lithocholic acid-binding activity after sequential gel filtration, chromatofocusing, and affinity chromatography. Three peaks of 3 alpha-HSD activity (I, II, III) were observed in chromatofocusing and all were identified on Western blot by a specific Y' binder antiserum. 3 alpha-HSD-I, the predominant form, was purified and functioned best as a reductase at pH with a marked preference for NADPH. Michaelis constant values for mono- and dihydroxy bile acids were 1-2 microM, and cholic acid competitively inhibited the reduction of 3-oxo-cholic acid. Under normal redox conditions, partially purified 3 alpha-HSD-I and freshly isolated hepatocytes catalyzed the rapid reduction of 3-oxo-cholic to cholic acid without formation of isocholic acid, whereas the reverse reaction was negligible. The Y' bile acid binders are therefore 3 alpha-HSD, which preferentially and stereospecifically catalyze the reduction of 3-oxo-bile acids to 3 alpha-hydroxy bile acids.

This gene encodes a member of the aldo/keto reductase superfamily , which consists of more than 40 known enzymes and proteins. These enzymes catalyze the conversion of aldehydes and ketones to their corresponding alcohols by utilizing NADH and/or NADPH as cofactors. The enzymes display overlapping but distinct substrate specificity. This enzyme catalyzes the reduction of prostaglandin (PG) D2, PGH2 and phenanthrenequinone (PQ), and the oxidation of 9alpha,11beta-PGF2 to PGD2. It may play an important role in the pathogenesis of allergic diseases such as asthma, and may also have a role in controlling cell growth and/or differentiation. This gene shares high sequence identity with three other gene members and is clustered with those three genes at chromosome 10p15-p14. [7]

3alpha hydroxysteroid reductase

3alpha hydroxysteroid reductase

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