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Results for “17-Hydroxysteroid Dehydrogenases”

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At least 19 recordsLinked to original sources
PubMed1978

The possible roles of membrane organization in the activity of androgen biosynthetic enzymes associated with normal or tumorous mouse Leydig cell microsomes.

The enzymes involved in conversion of pregnenolone to testosterone in Leydig cell tumors showed a wide distribution among smooth endoplasmic reticulum (SER), rough endoplasmic reticulum (RER), and cytosol, while these enzymatic activities in normal testes were associated primarily with smooth endoplasmic reticulum. Progesterone, used as a substrate in the presence of an NADPH-generating system, was metabolized to androstenedione and finally to testosterone by microsomes from some strains of tumor which did not form testosterone from exogenous labeled androstenedione. Treatment of microsomal membranes from normal testes with 0.1 M Ca++ and Mg++ caused a marked decrease in 17 beta-dehydrogenase activity, measured as conversion of exogenous [3H]androstenedione to [3H]-testosterone, without serious effects on activities of 3 beta-ol-dehydrogenase or 17 alpha-hydroxylase. Studies of initial velocity kinetics showed that treatment with magnesium ion resulted in a marked reduction in affinity of androstenedione for 17 beta-dehydrogenase while the maximum velocity was the same as in untreated microsomes. Also, experiments using [14C]progesterone and [3H]androstenedione simultaneously as substrates demonstrated that treatment with Mg++ ion made it more difficult for exogenous [3H]androstenedione to reach the active site of 17 beta-ol-dehydrogenase than [14C]androstenedione formed in the microsomal membrane from [14C]progesterone. Microsomal proteins were more easily solubilized and 3 beta-ol-dehydrogenase was more severely influenced by Mg++ ion in tumor membranes than in normal microsomes.

17-Hydroxysteroid Dehydrogenases↗
PubMed1979

Guinea pig liver aromatic aldehyde-ketone reductases identical with 17 beta-hydroxysteroid dehydrogenase isozymes.

Two NADPH-dependent aromatic aldehyde-ketone reductases purified from guinea pig liver catalyzed oxidoreduction of 17 beta-hydroxysteroids and 17-ketosteroids. One enzyme efficiently oxidized 5 beta-androstanes and reduced 17-ketosteroids of A/B cis configuration, whereas the other enzyme efficiently oxidized 5 alpha-androstanes and equally reduced both 5 alpha-and 5 beta-androstanes of 17-ketosteroids. However, aromatic aldehydes and ketones, and 3-ketosteroids were irreversibly reduced by the two enzymes. The two enzymes utilized NADP+ or NADPH as cofactor, but little activity with NAD+ or NADH was found. Phosphate ions enhanced the NAD+-dependent dehydrogenase activity and NADH-dependent reductase activity of the two enzymes, whereas the activities with NADP+ and NADPH were not affected. The ratios of the two activities of ketone reduction and 17 beta-hydroxysteroid oxidation of the two enzymes were almost constant during the purification steps after the two enzymes had been separated by DEAE-cellulose chromatography. By kinetic studies and electrophoresis and isoelectric focusing experiments it was confirmed that both of the two enzymes were responsile for the reduction aldehydes, ketones, and ketosteroids and for the oxidation of 17 beta-hydroxysteroids. These results indicate that 17 beta-hydroxysteroid dehydrogenases may play important roles in the metabolism of exogeneous aldehydes and ketones as well as steroids.

17-Hydroxysteroid Dehydrogenases↗
PubMed1979

Alkylation of estradiol 17 beta-dehydrogenase from human placenta with 3-chloroacetylpyridine--adenine dinucleotide phosphate.

3-Chloroacetylpyridine--adenine dinucleotide phosphate is both active as a hydride acceptor and inactivates estradiol 17 beta-dehydrogenase. This coenzyme analogue behaves like an affinity label. The inactivation kinetics are discussed in relation to those observed with 3-chloroacetylpyridine--adenine dinucleotide. The pH dependence of the rate of inactivation, in combination with determination of the number of reactive cysteine residues, pointed to the alkylation of one cysteine residue/subunit. The stoichiometry was one molecule of dinucleotide per subunit and no cooperativity was detected. When 14C-labeled dinucleotide was used, the 14C label was found mainly in one peptide, accounting for 90% of the incorporated radioactivity, whereas in previous work it had been shown that 3-chloroacetylpyridine--adenine dinucleotide is an affinity reagent which labels three peptides.

17-Hydroxysteroid Dehydrogenases↗
PubMed1978

Effects of 2-mercaptoethanol and aging in vitro on 17beta-hydroxysteroid oxidoreductase of guinea pig liver microsomes.

When microsomes were prepared in 2-mercaptoethanol Vmax for 17beta-hydroxysteroid oxidoreductase (17beta-HSD) was greater, the Km for NAD+ was greater and the Km for testosterone lower than in its absence. During storage at 4 degrees Vmax increased in the presence of 2-mercaptoethanol and decreased in its absence; Km values for testosterone and NAD+ increased during storage in both cases. The presence or absence of 2-mercaptoethanol did not affect the extent or time-course of inactivation of 17beta-HSD by trypsin or phospholipase A. Furthermore, no differences were detected in sedimentation properties on sucrose density gradients suggesting that the differences and changes in the kinetic behavior of 17beta-HSD reflect a conformational flexibility at the active site and are not due to extensive changes in the structure of the microsomes. 17beta-HSD exposed to 2-mercaptoethanol was subject to substrate inhibition by testosterone, a type of inhibition not previously reported for this enzyme.

17-Hydroxysteroid Dehydrogenases↗
PubMed1979

Some characteristics of 17 beta-estradiol dehydrogenase from bovine placenta.

The activity of 17 beta-estradiol dehydrogenase (E.C. 1.1.1.62) was measured, and its distribution in the subcellular fractions of bovine placenta was compared. Assay of activity was based on the formation of radioactive estrone from 17 beta[4(-14)C]-estradiol. Either NAD+ or NADP+ can serve as cofactor for the enzyme. The nuclear and microsomal fractions of the placental homogenate exhibited the highest specific enzymatic activities before and after treatment with Triton X-100. Electron micrographs of these two fractions prior to treatment with Triton X-100 showed satisfactory purity. 17 beta-estradiol dehydrogenase from bovine placenta exhibits a pH optimum of about 9.5-10.5, and is activated by 5 x 10(-6)M ZnCl2; comparable concentrations of CaCl2 and MgCl2 inactivate the enzyme. The apparent Michaelis constants, Km, for 17 beta-estradiol and NAD+ are 1.4 x 10(-6)M and 5.5 x 10(-5)M respectively. No 17 alpha-estradiol dehydrogenase activity was demonstrable when using 17 alpha-estradiol as substrate.

17-Hydroxysteroid Dehydrogenases↗
PubMed1977

Studies of the human testis. VIII. Product activation of 17beta-hydroxysteroid oxidoreductase for testosterone.

Cell-free homogenates prepared from human testis tissue were incubated with either 1.3 x 10(-5)M[4-14C]testosterone and 2 x 10(-4)M NADP or 1.3 x 10(-5) [4-14C]nadrostenedione and 2 x 10(-4)M NADPH. Addition of non-radioactive androstenedione and testosterone to the incubation medium increased the formation of [14C]androstenedione from [4-14C]testosterone and [14C]testosterone from [4-14C]androstenedione, respectively, while addition of product nucleotide NADPH or NADP, respectively, decreased the conversions. The addition of androstenedione to the incubation medium changed the apparent optimal pH of 17beta-hydroxysteroid oxidoreductase for testosterone from 8.6 to 8.0. It appears likely that in a cell-free system human testicular 17beta-hydroxysteroid oxidoreductase not solubilized and still attached to membrane is activated by the product of the reaction catalyzed by the enzyme.

17-Hydroxysteroid Dehydrogenases↗
PubMedDate not supplied

[Metabolism of sex steroid hormones in neuroendocrine organs. I. In vitro androgen metabolism in the hypophyses and epiphyses of rats during the puberal period].

Metabolism of tritium-labeled testosterone, delta4-androstane-3, 17-dion, dihydrotestosterone. 5alpha-androstane-3alpha, 17beta-diod and 5alpha-androstane-3beta, 17beta-dion by the isolated hypophyses and epiphyses of male and female 30-day rats was studied. The glands were incubated in Eagle's medium containing the mentioned androgens with the concentration of 1-2.10(-8) M for 90 min at 37 degrees C. As revealed, restoration of testosterone and delta4 androstane-3, 17-dion by 5alpha-reductase occurred in the epiphyses and hypophyses; under conditions of incubation androgen hydroxylation was realized only in the 3alpha- and 17beta-positions. Organ and sexual specificity of the androgen metabolism in the hypophyses and the epiphyses was quantitative in character: the metabolism level of all the androgens was greater in female rats than in the male both in the hypophysis and in the epiphyses; the activity of 5-reductase was lower in the epiphyses of animals of the both sexes than in the hypophyses. It appeared that in the process of biotransformation androgens in the organs under study served as precursors of the polar unidentified metabolites poorly retained by the tissues and eliminated from the organs into the incubation medium during the incubation.

15-Oxoprostaglandin 13-Reductase↗