Endocrinology, Vol 132, 1971-1976, Copyright © 1993 by Endocrine Society

ARTICLES

Enzyme characteristics of two distinct forms of mouse 3 beta- hydroxysteroid dehydrogenase/delta 5-delta 4-isomerase complementary deoxyribonucleic acids expressed in COS-1 cells

TR Clarke, PA Bain, L Sha and AH Payne
Department of Biological Chemistry, University of Michigan, Ann Arbor 48109-0278.

The enzyme 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4- Isomerase (3 beta HSD) catalyzes the conversion of delta 5-3 beta- hydroxysteroids to delta 4-3-ketosteroids, an essential step in the biosynthesis of all biologically active steroid hormones. We previously reported the isolation of three distinct mouse cDNAs for 3 beta HSD (3 beta HSD I, II, and III) and tissue-specific expression of their mRNAs. 3 beta HSD I is expressed only in gonads and adrenal glands, and 3 beta HSD II and III are expressed in both liver and kidneys. In the current study, we present data which demonstrate that transiently expressed 3 beta HSD I and 3 beta HSD III proteins can catalyze the conversion of the delta 5-steroids, pregnenolone and dehydroepiandrosterone, to their respective delta 4-3-ketosteroids, progesterone and androstenedione. They also can dehydrogenate the 3 beta-hydroxy group of the 5 alpha- reduced steroid 5 alpha-androstanediol to yield dihydrotestosterone in the presence of the cofactor NAD+. The Km values of the expressed 3 beta HSD I (for each of these substrates) were all below 0.2 microM. Km values of 3 beta HSD III were greater for all substrates, with the greatest increase observed for pregnenolone, which was over 10-fold greater. Both forms of expressed protein can catalyze the reduction of dihydrotestosterone to 5 alpha-androstanediol in the presence of the cofactor NADH, but with considerably higher Km values (5.5 microM for form I and 6.8 microM for form III). The observed maximum velocity of form I was much higher for all substrates examined. RNase protection and immunoblot analysis of expressed 3 beta HSD I and III indicate that the difference in maximum velocity reflect differences in the steady state levels of mRNA and amounts of protein. In addition, the expressed 3 beta HSD III protein analyzed by Western blot has a lower mobility than the 3 beta HSD I protein, both similar in mol wt to the 3 beta HSD proteins detected in mouse liver and adrenal glands, respectively. These data demonstrate that an isoform of 3 beta HSD expressed in liver and kidney has the capacity to convert delta 5-3 beta-hydroxysteroids to delta 4-3-ketosteroids. The data suggest that a homologous human 3 beta HSD isoform could play an important role in cases of genetic deficiency of the gonadal and adrenal isoform.

This article has been cited by other articles:

				J. Simard, M.-L. Ricketts, S. Gingras, P. Soucy, F. A. Feltus, and M. H. Melner Molecular Biology of the 3{beta}-Hydroxysteroid Dehydrogenase/{Delta}5-{Delta}4 Isomerase Gene Family Endocr. Rev., June 1, 2005; 26(4): 525 - 582. [Abstract] [Full Text] [PDF]

				A. H. Payne and D. B. Hales Overview of Steroidogenic Enzymes in the Pathway from Cholesterol to Active Steroid Hormones Endocr. Rev., December 1, 2004; 25(6): 947 - 970. [Abstract] [Full Text] [PDF]

				I. G. Abbaszade, J. Arensburg, C.-H. J. Park, J. Z. Kasa-Vubu, J. Orly, and A. H. Payne Isolation of a New Mouse 3{beta}-Hydroxysteroid Dehydrogenase Isoform, 3{beta}-HSD VI, Expressed During Early Pregnancy Endocrinology, April 1, 1997; 138(4): 1392 - 1399. [Abstract] [Full Text] [PDF]

				P. L. Pettersson and B. Mannervik The Role of Glutathione in the Isomerization of Delta 5-Androstene- 3,17-dione Catalyzed by Human Glutathione Transferase A1-1 J. Biol. Chem., April 6, 2001; 276(15): 11698 - 11704. [Abstract] [Full Text] [PDF]