title: The substrate specificity and stereochemistry, reversibility and inhibition of the 3-oxo steroid delta 4-delta 5-isomerase component of cholesterol oxidase.
abstract: 1. 5-Cholesten-3-one was shown to be an intermediate in the conversion of cholesterol into 4-cholesten-3-one by Nocardia cholesterol oxidase. 2. The absence of a C-17 side chain from 5-androstene-3,17-dione slightly increased the Vmax. of the isomerase activity relative to 5-cholesten-3-one (1.7-fold), but greatly increased the Km. 3. Incubations of [4alpha-2H]-and [4beta-2H]-cholesterol with cholesterol oxidase showed that the 4beta-hydrogen atom can be transferred to the 6beta-position. However, incubations of cholesterol, 5-cholesten-3-one and 4-cholesten-3-one with the enzyme in 2H2O led to some incorporation of 2H into the 4-cholesten-3-one products, mostly at position 6beta. 4. Both the isomerase and the oxidase activities of cholesterol oxidase were inhibited by 5,10-seco-19-nor-5-cholestyne-3,10-dione.
mesh_terms: D015096:3-Hydroxysteroid Dehydrogenases / Q000378:metabolism*; D002783:Cholestenones / Q000096:biosynthesis / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism; D002789:Cholesterol Oxidase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007535:Isomerases / Q000037:antagonists & inhibitors*; D007700:Kinetics; D011487:Protein Conformation; D012632:Secosteroids / Q000494:pharmacology; D013251:Steroid Isomerases / Q000037:antagonists & inhibitors*; D013379:Substrate Specificity; D014316:Tritium
chemical_list: C016097:5,10-seco-19-nor-5-cholestyne-3,10-dione; D002783:Cholestenones; D012632:Secosteroids; D014316:Tritium; D002784:Cholesterol; D015096:3-Hydroxysteroid Dehydrogenases; D002789:Cholesterol Oxidase; D007535:Isomerases; D013251:Steroid Isomerases