title: Isolation of 3 beta,20 alpha-hydroxysteroid oxidoreductase from sheep fetal blood.
abstract: 3 beta,20 alpha-Hydroxysteroid oxidoreductase has been isolated from ovine fetal blood by a 2,370-fold purification scheme of ammonium sulfate fractionation, calcium phosphate gel adsorption, affinity chromatography, and fast performance liquid chromatography. A new high performance liquid chromatography-based assay for measuring 20 alpha-reductase activity is described. The enzyme is a monomer with a molecular weight of 35,000 and uses NADPH as a cofactor for reductase activity. It reduces progesterone to 4-pregnen-20 alpha-ol-3-one or 5 alpha-dihydrotestosterone to 5 alpha-androstan-3 beta,17 beta-diol with kinetic characteristics of Km = 30.8 microM and Vmax = 0.7 nmol min-1 (nmol of enzyme)-1 or Km = 74 microM and Vmax = 1.3 nmol min-1 (nmol of enzyme)-1, respectively. 5 alpha-Dihydrotestosterone competitively inhibits 20 alpha-reductase activity with a Ki value of 102 microM.
mesh_terms: D000818:Animals; D002417:Cattle; D004912:Erythrocytes / Q000201:enzymology; D005312:Fetal Blood / Q000201:enzymology*; D006913:Hydroxysteroid Dehydrogenases / Q000097:blood*; D007700:Kinetics; D008970:Molecular Weight; D012756:Sheep; D013045:Species Specificity
chemical_list: D006913:Hydroxysteroid Dehydrogenases; C036177:3 beta,20 alpha-hydroxysteroid oxidoreductase