Subcellular localization of 3ß hydroxysteroid dehydrogenase 5-ene isomerase in testis of Bufo arenarum H

POZZI AG; LANTOS CP; CEBALLOS N

GENERAL AND COMPARATIVE ENDOCRINOLOGY

Elsevier

Lugar: Londres; Año: 1997 vol. 106 p. 400 - 406

0016-6480

3b-hydroxysteroid dehydrogenase 5-ene isomerase (3bHSD/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., 3bHSD/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 3bHSD/I were determined by the oxidation of pregnenolone and dehydroepiandrosterone. The preferred substrate of the microsomal 3bHSD/I enzyme was dehydroepiandrosterone (Km 5 0.17 mM and 0.53 mM for dehydroepiandrosterone and pregnenolone, respectively) not only during the breeding season but also in the nonbreeding period (Km 5 0.49 mM and 2.9 mM for dehydroepiandrosterone and pregnenolone, respectively).b-hydroxysteroid dehydrogenase 5-ene isomerase (3bHSD/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., 3bHSD/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 3bHSD/I were determined by the oxidation of pregnenolone and dehydroepiandrosterone. The preferred substrate of the microsomal 3bHSD/I enzyme was dehydroepiandrosterone (Km 5 0.17 mM and 0.53 mM for dehydroepiandrosterone and pregnenolone, respectively) not only during the breeding season but also in the nonbreeding period (Km 5 0.49 mM and 2.9 mM for dehydroepiandrosterone and pregnenolone, respectively).