Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0338671 (Steroids)
 9,479 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Delta5-3beta HSDH activity has been assayed either by spectrophotometric method or by use of radioactive substrates. The enzymatic activity is equally distributed between mitochondrial and microsomal fractions verified by electronic microscopy. The specific activity is comparable in both fractions, as well as the optimal pH and the Km for NAD and for the substrates. The delta5-3beta Hut optimal pH, specific activity and sensitivity to the inhibitory action of various steroids are different when C19 and C21 steroids are used as substrates. Estrogens and cyclic AMP have also an inhibitory action on the oxidation of C21 steroids. Treatment of microsomal or mitochondrial membranes with phospholipase A releases fatty acids (mainly arachidonic) and decreases the enzymatic activity. "Adsorbtion" of the fatty acids on bovine serum albumin partially reactivates the delta5-3beta HSDH.
Steroids 1975 Nov
PMID:Human placental delta5-3beta hydroxysteroid dehydrogenase activity (delta5-3beta HSDH): intracellular distribution, kinetic properties, retroinhibition and influence of membrane delipidation. 0 79

Stoll specimens from 3 healthy volunteers were cultured under an-aerobic conditions in brain heart infusion broth with and without the addition of cholate, deoxycholate of chenodeoxycholate. The initial pH of the medium was adjusted to 5.5, 6.3, 7.3 (unadjusted), 8.0, and 9.0. Cell-free extracts prepared from the resulting bacterial growth contained increased levels of NAD- and NADP-dependent 3alpha-, 7alpha-, and 12alpha-hydroxysteroid oxidoreductases when the initial pH was 8.0 or 9.0 and depressed levels of these activities when the initial pH was 5.5 or 6.3 (as compared to control values obtained at 7.3). At pH 5,5 all activities except NAD-dependent 7alpha-hydroxysteroid oxidoreductase were absent. A powerful selective effect was imposed on NAD-dependent 7alpha-hydroxysteroid oxidoreductase when deoxycholate or chenodeoxycholate were incorporated into or chenodeoxycholate were incorporated into the medium. Thin-layer chromatography of either extracts of cholate-containing, acidified spent bacterial medium showed alkaline or neutral (optimal at pH 8). The precent hydroxyl group estimations at the 3alpha-, 7alpha-, and 12alpha-positions revealed an increase in disappearance of OH groups at all three positions with increasing initial pH value. The order of extent of bioconversion was 7alpha-OH greater than 3alpha-OH; at pH 8 AND 9, approximately 90% 7alpha-OH bioconversion was observed. Spent bacterial media and a number of commercial secondary bile salts were all negative in the Ames' assay for mutagenicity.
Steroids 1978 Sep
PMID:Effect of pH on bile salt degradation by mixed fecal cultures. 3 Oct 16

A 3beta-hydroxysteroid dehydrogenase (3betaHSD) was demonstrated in term human fetal membranes (chorion and amnion) with both dehydroepiandrosterone (3beta-hydroxy-5-androsten-17-one) and pregnenolone (3beta-hydroxy-5-pregnen-20-one as substrates, and the subcellular distribution substrate and nucleotide specificity of the enzyme was studied. In both membranes the microsomal fraction (particles which sedimented at 105,000 g after 90 min) had the highest specific activity. The chorion was more active than the amnion but the enzyme in both tissues had similar substrate and nucleotide specificity. NAD was the preferred cofactor, and pregnenolone was a better substrate than dehydroepiandrosterone in the presence of NAD. However, with NADP as cofactor both steroids were equally good substrates. When the 3beta-hydroxysteroid dehydrogenase activity of chorion microsomes was compared with that of placental microsomes, the specific activities were found to be of the same order of magnitude, and the substrate, nucleotide specificity and steroid binding properties were almost identical.
Steroids 1978 Oct
PMID:3beta-Hydroxysteroid dehydrogenase activity in human fetal membranes. 3 Oct 18

The properties of 5-ene-3 beta hydroxysteroid oxidoreductase (3 beta-HSD) from human placental homogenates were studied in vitro. The apparent Michaelis constants for 3 beta-HSD with the substrates pregnenolone (delta 5P) and dehydroepiandrosterone (DHA) were 170 nM and nM respectively. The optimal pH for both these substrates was between 10 and 12. With NAD as the substrate, the Km for the pregnenolone was 20 microM and for DHA, 17 microM. The activity of 3 beta-HSD was inhibited by various steroids. Competitive inhibitors (pregnenolone substrate) included: ethynylestradiol (inhibition constant Ki=7.3 nM), DHA (Ki=46 nM), estradiol-17 beta (Ki=46 nM), cholesterol (Ki=0.68 microM) and 16 alpha-hydroxydehydroepiandrosterone (16 alphaOHDHA) (Ki=2.2 microM). When the substrate was DHA, competitive inhibition occurred with the following steroids: ethynylestradiol (Ki=6.4 nM), estradiol-17 beta (Ki=69 nM), pregnenolone (Ki=91 nM), cholesterol (Ki=1.3 microM) and 16 alphaOHDHA (Ki=1.9 microM). 4-Ene-3-ketosteroids such as androstenedione, progesterone (delta 4P), norethindrone and chlormadinone acetate acted as noncompetitive inhibitors towards both substrates.
Steroids 1979 Jan
PMID:Steroid specificity of human placental 5-ene-3 beta-hydroxysteroid oxidoreductase. 3 90

After addition of estrone to rat liver slices, a quotient of estradiol/estrone of ca. 0.1 is reached within 1 - 2 min. By additional application of 17 beta-hydroxysteroids this quotient is changed in the direction of estradiol, although the applied concentrations of both steroids are far below the concentration of the cytoplasmic redox couple NADH/NAD. Of all the steroids tested, testosterone had the strongest influence on the quotient, especially in the liver of female rats. This influence is smaller in the livers of male rats and infantile animals. The changing of the E2/E1 quotient by testosterone can be inhibited by the antiandrogen cyproteron acetate. Steroids with hydroxy groups at C-3 or C-20 or high concentrations of non-steroids, which can be oxidized by NAD, change the E2/E1 quotient only minimally. The experiments demonstrate that in liver, the redox couple estradiol/estrone is not in equilibrium with the main redox couple of the cytoplasmic NADH/NAD. Only on account of this fact it is possible that relatively low concentrations of testosterone change the E2/E1 quotient via the C-17 leads to C-17 hydrogen transfer between steroids. Biological consequences are discussed.
 ...
PMID:[Increased estradiol-estrone quotient in rat liver by hydroxysteroids: an effect of the specific hydrogen transfer between steroids]. 16 43

The biotransformation of estradiol (E2) and estrone (E1) in the uterus of rabbits treated with norgestrel (NG), norethindrone (NET), norethindrone acetate (NETA), progesterone (P4), and E2 either by subcutaneous injection in oil or by intrauterine steroid-releasing silastic implants was carried out under an in vitro short-term incubation system. The studies have shown that E2 stimulates 17 beta-hydroxysteroid dehydrogenase (17 beta-OHSD) much more than P4 as compared to untreated controls. The kinetic studies on E2 metabolism in the presence of added coenzyme NAD showed an initial rapid estrone formation and a gradual reconversion of E1 to E2. The addition of NADPH, ATP, and glucose-6-phosphate facilitates the reconversion of E1 to E2. The interconversion of E2 and estrone in the presence of coenzymes was five- to ten-fold higher in the endometrium than in the myometrium per milligram protein. Both E2 and progestins stimulate the uterine 17 beta-OHSD activity in rabbit uterus. This study further suggested that the hormone-induced metabolism of estradiol and estrone in the rabbit uterus is essentially modulated by the availability of coenzymes.
Steroids 1989 Jun
PMID:Effect of progestins, estradiol, and coenzymes NAD and NADPH on the interconversion of estradiol and estrone in rabbit uterus in vitro. 255 42

A novel A-ring pyrazole steroid, 2,3-bisaza-A-nor-1,5(10)-estradien-17 beta-ol (3), was synthesized as a potential inhibitor of steroidal NAD(P)H-dependent oxidoreductases. Compound 3 proved to be a potent inhibitor of 3(17)beta-hydroxysteroid dehydrogenase (from P. testosteroni) exhibiting a Ki of 90 +/- 20 nM. The activities of 3 alpha,20 beta-hydroxysteroid dehydrogenase (from S. hydrogenans), steroid-5 alpha-reductase (from rat prostate), and 3 alpha-hydroxysteroid dehydrogenase (from rat liver) were unaffected by pyrazole 3. Dead end inhibition studies indicate an ordered binding of cofactor prior to substrate or pyrazole inhibitor.
Steroids
PMID:Inhibition of pyridine-nucleotide-dependent enzymes by pyrazoles. Synthesis and enzymology of a novel A-ring pyrazole steroid. 348 87

A rapid, precise, and accurate photometric method for determining free and esterified fecal 3 alpha-hydroxy bile acids is described. Feces are homogenized and (a) extracted with boiling absolute ethanol, or (b) lyophilized and extracted with chloroform:methanol 2:1 (v/v). Hydrolyzed and nonhydrolyzed crude extracts are prepared and aliquots treated with a reagent containing nitro blue tetrazolium (NBT), 3 alpha-hydroxysteroid oxidoreductase, beta-nicotinamide adenine dinucleotide (beta-NAD) and diaphorase. The reagent first oxidizes bile acid 3 alpha-hydroxyls to 3-oxo groups and 3 beta-hydrogen is transferred to beta-NAD yielding beta-NADH. beta-NADH in turn reduces NBT (yellow) to its diformazan (blue). Absorbance is measured at 540 nm and is proportional to the 3 alpha-hydroxy bile acid titer of fecal extract aliquots. Fecal pigments present in crude extracts do not interfere with the assay since they absorb minimally at 540 nm.
Steroids 1983 Jun
PMID:Rapid photometric determination of free and esterified 3 alpha-hydroxy fecal bile acids. 666 19

The interconversion of estradiol-17 beta and estrone in the rat uterus is due to the action of 17 beta-hydroxysteroid dehydrogenase. Whole uteri or 800 x g supernatant fractions of the uteri were incubated in the presence of [3H] estradiol-17 beta and NAD at 37 degrees C for 3 h or 1 h, respectively. In the mature rat uterus the oxidation of estradiol-17 beta and estrone was dependent on the stage of the estrous cycle, suggesting hormonal control. The 17 beta-hydroxysteroid dehydrogenase activity was highest at estrus (200 fmol estrone) and lowest at diestrus (80 fmol estrone). An enhancement of activity occurred when adult rats at each stage of the estrous cycle were administered estradiol-17 beta, while progesterone administration at each stage resulted in decreased enzyme activity. The uterine 17 beta-hydroxysteroid dehydrogenase activity of estradiol-17 beta treated ovariectomized rats was time and dose dependent but decreased when progesterone was administered with or without estradiol-17 beta administration. These results suggest that estradiol-17 beta caused an increase in enzyme activity that was inhibitable by progesterone in the rat uterus. The increased 17 beta-hydroxysteroid dehydrogenase activity may reflect a specific response of the rat uterus to estradiol-17 beta.
Steroids 1980 Jul
PMID:Steroidal control of rat uterine 17 beta-hydroxysteroid dehydrogenase activity. 693 5

From rat liver microsomes a NAD: 3 alpha-hydroxy-5 alpha-pregnan-20-one oxidoreductase was isolated and purified up to a specific activity of 73 nmol/min . mg by affinity chromatography and DEAE-cellulose chromatography. Various Km-values have been determined. The enzyme exhibits highest affinity for 5 alpha-pregnane-3,20-dione and NADH. The 3-oxo group of 5 alpha-dihydrocortisone (17,21-dihydroxy-5 alpha-pregnane-3,11,20-trione) was not reduced by the purified enzyme preparation and NADH and no dehydrogenation with NAD was observed of 3 alpha,11 beta,17,21-tetrahydroxy-5 alpha-pregnan-20-one. The optimal pH for the hydrogenation of th 3-oxo group was at pH 5.3 and for the dehydrogenation at pH 8.9. Disc gel electrophoresis in presence of 0.1% sodium dodecylsulfate yielded a homogeneous preparation.
Steroids 1980 Aug
PMID:Purification and properties of a NAD: 3 alpha-hydroxy-5 alpha-pregnan-20-one-oxidoreductase from rat liver microsomes. 693 32


1 2 3 4 Next >>