Solubilization and separation of delta5,3beta-hydroxysteroid dehydrogenase and 3-oxosteroid-delta4-delta5-isomerase from bovine adrenal cortex microsomes

3 beta-Hydroxysteroid dehydrogenase in human placental microsomes and mitochondria: co-solubilization of androstene and pregnene activities

3 beta-Hydroxysteroid dehydrogenase (3 beta-HSD) was solubilized from human term-placental microsomes and mitochondria using the non-ionic detergent, polyoxyethylene 20 cetyl ether (BrijR-58). Electron photomicrographs showed microsomes and mitochondria well disrupted by the detergent. The pregnene (C-21) and androstene (C-19) activities co-solubilized over a range (0.04-0.44) of BrijR-58/protein (B/P) concentration ratios (w/w). Optimal solubilization of the C-19 and C-21 activities were 63.3 +/- 2.6% (mean +/- SEM) from mitochondria (B/P ratio 0.37) and 71.8 +/- 2.1% from microsomes (B/P ratio 0.34). Detergent treatment of microsomes and mitochondria--varying time (5-90 min, pH 7.4) or varying pH (6.0-7.8, 90 min)--yielded C-19 activities identical with C-21 activities. The C-21/C-19 specific activity ratios of 3 beta-HSD in particulate, solubilized and chromatographed preparations were 2.28 +/- 0.16 (mean +/- SEM) for mitochondria and 1.97 +/- 0.07 for microsomes. 3 beta-HSD molecular weight estimates were 208,000 (microsomes) and 220,000 (mitochondria). These studies argue that a single protein is responsible for both the C-19 and C-21 activities of 3 beta-HSD and that this protein is the same in microsomes and mitochondria.

Effect of membrane lipid environment on the activity of bovine adrenal 3-oxo-delta 5-steroid isomerase

The 3-oxo-delta 5-steroid isomerase (EC 5.3.3.1) activity from bovine adrenal cortex microsomes can be extracted in soluble form by the use of appropriate detergents, although recovery of enzyme activity is low (ca. 2%). Activity is restored upon removal of detergent and reconstitution of the enzyme into phospholipid vesicles. Both Km and Vmax of 3-oxo-delta 5-steroid isomerase of intact microsomes increase as the pH is raised from 7.5 to 9.5, with a particularly sharp increase (6- to 8-fold) above pH 8.5. The kinetic parameters of a detergent-solubilized isomerase preparation show little increase from pH 7.5 to 9.0, but isomerase reconstituted into artificial phospholipid vesicles demonstrates a 6- to 10-fold increase in both Km and Vmax over this pH range. Addition of Ca++ (1 mM) enhances the pH dependence of both Km and Vmax of the membrane-bound isomerase, causing a slight rise in Vmax/Km.

Characterization of a nonenzymatic component in the isomerization of 5-pregnene-3,20-dione catalyzed by human placental microsomes in vitro

When human placental microsomes were heated in boiling water or exposed to trypsin, 30 to 40% of the 5-ene,3-ketosteroid isomerase activity was stable. Aqueous suspensions of chloroform:methanol extracts of microsomes also catalyzed isomerization of 5-pregnene-3,20-dione, activity being associated with the polar lipid fraction. The trypsin- and heat-stable activities, as well as that of resuspended microsomal lipids, showed a dependence on buffer composition and concentration. Little activity was detected in water at pH 7.0. Relative activities in various buffers were Hepes (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) greater than Pipes (1,4-piperazinediethanesulfonic acid) greater than potassium phosphate greater than Mes(4-morpholineethanesulfonic acid). The data suggest that the occurrence of membrane lipid-dependent nonenzymatic catalysis could contribute to the isotope exchange with solvent observed in previous studies of the mechanism of isomerization catalyzed by placental microsomes. The ability of the membrane lipid phase to catalyze steroid isomerization under certain conditions and the fact that this activity is subject to modifications by exogenous agents may have more general implications for an understanding of possible effects of xenobiotics on steroid hormone formation and action in vivo.

Microsomal 5-ane-3 beta-hydroxysteroid oxidoreductase from pubertal rat Leydig cells: partial purification and characterization

A 3 beta-hydroxysteroid oxidoreductase which acts on 5 alpha (beta)-reduced C19 and C21 steroids (5-ane-3 beta-hydroxysteroid oxidoreductase; 5-ane-3 beta-HSO) has been solubilized from pubertal rat Leydig cell microsomes and purified 300-fold by ion exchange and gel filtration chromatography. The partially purified enzyme is stable only in the presence of 0.4 M NaCl and appears to exist as a molecule having a molecular weight of 35,000 or as aggregates with a molecular weight in excess of 150,000. NAD+ and NADH+ are used exclusively as cofactors. The velocity of the steroid oxidation reaction was unaffected by either Ca2+ or Mg2+. The steroid oxidation reaction has a pH optimum between 8.0 and 8.5, a temperature optimum at 35 degrees C and an activation energy of 12,850 cal/mol. The pH optimum of the steroid reduction reaction is 6.6. A variety of 5 alpha-reduced C19 and C21 steroids can be utilized as substrates. Treatment of microsomes with phospholipase A2 resulted in a 26 to 90% loss of enzyme activity, paralleling decreased microsomal phospholipid content, and suggesting a role for phospholipids in 5-ane-3 beta-HSO activity. Assays with combined substrates indicate that one enzyme is responsible for activities observed with 5 alpha- and 5 beta-reduced C19- and 5 alpha-reduced C21-3 beta-hydroxysteroids. Purification data indicate that the 5-ane-3 beta-HSO and the 5-ene-3 beta-hydroxysteroid oxidoreductase:isomerase are distinct enzymes.

Properties of 5-ene-3 beta-hydroxysteroid dehydrogenase in granulosa tissue from the domestic fowl (Gallus domesticus)

Microsomal 5-ene-3 beta-hydroxysteroid dehydrogenase activity from fowl preovulatory granulosa tissue was solubilised by treatment with 2.0 M KCl. The efficiency of the solubilisation procedure was assessed by measuring the amount of activity remaining in the supernatant after centrifugation at 105,000 g for 8 h. The microsomal activity was resolved into two components: a fraction solubilised by the salt treatment and a fraction remaining membrane bound. The results indicate that the enzyme exists in two different environments within the membrane. The time course for the thermal inactivation of the microsomal enzyme supported this conclusion. The properties of the solubilised enzyme were compared with the untreated microsomal preparation, with respect to steroidal inhibition. Progesterone, 4-androstene-3,17-dione and oestradiol-17 beta all inhibited the enzyme and no difference was observed between the two preparations. The results are discussed in relation to the involvement of 5-ene-3 beta-hydroxysteroid dehydrogenase in the control of progesterone production in fowl granulosa tissue.