title: Subcellular localization and properties of mouse adrenal C19-steroid 5beta-reductase.
abstract: The localization and some characteristics of mouse adrenal C19-steroid 5 beta-reductase were determined by the incubation of subcellular fractions of mouse adrenal tissue with [7 alpha-3H]androst-4-ene-3,17-dione. This enzyme was present only in the soluble fraction and was NADPH-dependent, although a small activity in the presence of NADH was also detected. The soluble fraction also contained 3alpha-, 3beta- and a small amount of 17 beta-hydroxy steroid dehydrogenase. These and other steroid-metabolizing enzymes present in the remaining subcelluar fractions are also described briefly. To measure 5 beta-androstane-3,17-dione production by the mouse adrenal soluble fraction, all 5 beta products first had to be oxidized to 5 beta-androstane-3,17-dione, and the recovery of radio-activity between the substrate androst-4-ene-3,17-dione and product 5 beta-androstane-3,17-dione of 96.1 +/-3.2% validated this technique. C19-steroid 5 beta-reductase has a pH optimum of 6.5 and at low substrate concentrations the Km and Vmax. for 5 beta reduction of [7 alpha-3H]androst-4-ene-ene-3,17-dione was 2.22 times 10(-6) "/- 0.48 times 10(-6) M and 450+/- 53 pmol/min per mg of protein respectively. At high substrate concentration, inhibition of the reaction occurred, which was shown to be due to increasing product concentration.
mesh_terms: D000311:Adrenal Glands / Q000201:enzymology* / Q000648:ultrastructure; D000731:Androstanes / Q000378:metabolism; D000735:Androstenedione / Q000378:metabolism; D000818:Animals; D006913:Hydroxysteroid Dehydrogenases / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D009243:NAD; D009249:NADP; D013250:Steroid Hydroxylases / Q000378:metabolism*; D013347:Subcellular Fractions / Q000201:enzymology; D013739:Testosterone
chemical_list: D000731:Androstanes; D009243:NAD; D013739:Testosterone; D000735:Androstenedione; D009249:NADP; D006913:Hydroxysteroid Dehydrogenases; D013250:Steroid Hydroxylases