title: Rat Leydig cell and granulosa cell 17-ketosteroid reductase activity: subcellular localization and substrate specificity.
abstract: The potent gonadal steroids testosterone and estradiol are synthesized from the biologically weak precursors, androstenedione and estrone, by enzymatic reduction of the ketone group at carbon-17 of the steroid nucleus (17-ketosteroid reductase). To test the hypothesis that Leydig and granulosa cells may contain a distinct 17-ketosteroid reductase enzyme, the subcellular localization and the substrate specificity of the enzyme was examined in each cell type. In Leydig cells, the 17-ketosteroid reductase activity was concentrated in the microsomal fraction of the cell. In granulosa cells, the 17-ketosteroid reductase activity was concentrated in the cytosolic fraction of the cell. In Leydig cell microsomes, the apparent Michaelis-Menten constant for the conversion of androstenedione to testosterone was 0.41 mumol/L and for the conversion of estrone to estradiol it was 12 mumol/L. In granulosa cell cytosol, the apparent Michaelis-Menten constant for the conversion of estrone to estradiol was 1.1 mumol/L and for the conversion of androstenedione to testosterone it was 15 mumol/L. These results demonstrate that rat Leydig and granulosa cells each contain a 17-ketosteroid reductase enzyme with unique subcellular localization and substrate specificity.
authors.affiliation: Department of Obstetrics, Gynecology and Reproductive Biology, Brigham and Women's Hospital, Boston, MA 02115.
authors.forename: R L
authors.initials: RL
authors.lastname: Barbieri
authors.forename: M S
authors.initials: MS
authors.lastname: Rein
authors.forename: M D
authors.initials: MD
authors.lastname: Hornstein
authors.forename: K J
authors.initials: KJ
authors.lastname: Ryan
mesh_terms: D015067:17-Hydroxysteroid Dehydrogenases / Q000378:metabolism*; D000735:Androstenedione / Q000378:metabolism; D000818:Animals; D004958:Estradiol / Q000096:biosynthesis; D004970:Estrone / Q000378:metabolism; D005260:Female; D006107:Granulosa Cells / Q000201:enzymology*; D007985:Leydig Cells / Q000201:enzymology*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013347:Subcellular Fractions / Q000201:enzymology; D013379:Substrate Specificity; D013739:Testosterone / Q000096:biosynthesis; D014018:Tissue Distribution
chemical_list: D004970:Estrone; D013739:Testosterone; D000735:Androstenedione; D004958:Estradiol; D015067:17-Hydroxysteroid Dehydrogenases