title: Subcellular localization of 3 beta hydroxysteroid dehydrogenase isomerase in testis of Bufo arenarum H.
abstract: 3 Beta-hydroxysteroid dehydrogenase 5-ene isomerase (3 beta HSD/I) catalyzes an essential step in the biosynthesis of steroid hormones and is usually considered to be mainly microsomal, although there is a dual distribution of the enzyme in toad interrenals. The present study demonstrates that in the testicular tissue, as in interrenals of Bufo arenarum H., 3 beta HSD/I is both mitochondrial and microsomal. The conversion of dehydroepiandrosterone to androstenedione takes place only in microsomes while pregnenolone is converted to progesterone in both microsomes and mitochondria. Kinetic constants of 3 beta HSD/I were determined by the oxidation of pregnenolone and dehydroepiandrosterone. The preferred substrate of the microsomal 3 beta HSD/I enzyme was dehydroepiandrosterone (K(m) = 0.17 microM and 0.53 microM for dehydroepiandrosterone and pregnenolone, respectively) not only during the breeding season but also in the non-breeding period (K(m) = 0.49 microM and 2.9 microM for dehydroepiandrosterone and pregnenolone, respectively).
authors.affiliation: PRHOM-CONICET, Departamento de Ciencias Biológicas, Universidad de Buenos Aires, Argentina.
authors.forename: A G
authors.initials: AG
authors.lastname: Pozzi
authors.forename: C P
authors.initials: CP
authors.lastname: Lantos
authors.forename: N R
authors.initials: NR
authors.lastname: Ceballos
mesh_terms: D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase / Q000378:metabolism; D000818:Animals; D002022:Bufo arenarum; D003687:Dehydroepiandrosterone / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008861:Microsomes / Q000201:enzymology; D008928:Mitochondria / Q000201:enzymology; D009097:Multienzyme Complexes / Q000032:analysis*; D011284:Pregnenolone / Q000378:metabolism; D011374:Progesterone / Q000378:metabolism; D011375:Progesterone Reductase / Q000032:analysis*; D011506:Proteins / Q000032:analysis; D012098:Reproduction; D013251:Steroid Isomerases / Q000032:analysis*; D013347:Subcellular Fractions / Q000201:enzymology; D013737:Testis / Q000201:enzymology*
chemical_list: C021425:3 beta-hydroxysteroid oxidoreductase-delta(5) 3-ketosteroid isomerase; D009097:Multienzyme Complexes; D011506:Proteins; D003687:Dehydroepiandrosterone; D011374:Progesterone; D011284:Pregnenolone; D011375:Progesterone Reductase; D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase; D013251:Steroid Isomerases