Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:Q8NEX9 (reductase)
 26,410 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Microsomal estrogen synthetase (cytochrome P-450ES), also known as aromatase, was purified from fresh human placenta microsomes by DEAE-Trisacryl and testosterone-agarose chromatography. Estrogen synthetase assays were done with androstenedione as substrate, NADPH as electron donor, and a partially purified P-450 reductase from human placenta as the electron carrier. The specific cytochrome P-450 content of the purified P-450 was 0.67 nmol mg-1 of protein, and the preparation contained no cytochrome P-420. The absorbance maximum was 448.5 nm. The specific estrogen synthetase activity of the purified P-450ES fraction was 35 nmol min-1 nmol-1 of cytochrome P-450 or 23.3 nmol min-1 mg-1 of protein. The latter value shows a 179-fold purification with a yield greater than 1% in the two-step procedure. Kinetic constants for the reaction were measured with androstenedione as the aromatizable substrate. The Km was 1.4 nM and the Vmax was 37 nmol min-1 nmol-1 of P-450. The purified enzyme aromatized androstenedione and testosterone at identical rates; androstenedione gave only estrone, and testosterone gave only estradiol-17 beta. Dehydroepiandrosterone was not detectably aromatized or otherwise metabolized. Neither 16 alpha-hydroxytestosterone nor 16 alpha-hydroxyandrostenedione was aromatized. No hydroxysteroid dehydrogenase or reductase was detected in direct assays. No free reaction intermediates were detected in aromatization assay incubation mixtures. The purity of the product and the simplicity of the preparation recommend it for use in further studies of the enzyme.
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PMID:Human placenta estrogen synthetase (aromatase) purified by affinity chromatography. 381

4-hydroxy-4-androstene-3,17-dione (4-OHA) has been shown to be a potent inhibitor of aromatase activity. It is effective in the control of estrogen-dependent processes in female subjects and may potentially be useful in the treatment of estrogen-dependent processes in men. Human foreskin fibroblasts grown in cell culture provide a model to investigate the effects of 4-OHA on extraglandular aromatase activity as well as the ability of the compound to influence androgen receptor binding and the 5 alpha-reduction of testosterone (T). Initial experiments were carried out to determine the potency of 4-OHA in genital skin fibroblasts by incubating cells with 4-OHA over a range of concentrations. When aromatase activity was determined at a substrate concentration close to the apparent Km of the enzyme, a 44% inhibition of enzyme activity occurred at a mean concentration of 5 nM 4-OHA. Enzyme kinetic studies analyzed by Eadie-Hofstee plots demonstrated competitive inhibition by 4-OHA with a mean apparent Ki of 2.7 nM. When 5 alpha-reductase activity was determined in the presence of 200 nM [3H]T, in the absence or presence of 4-OHA, a 50% inhibition of enzyme activity occurred at an inhibitor concentration of 3 microM. In androgen receptor binding studies, 4-OHA possessed 1% of the affinity of dihydrotestosterone (DHT) for [3H]DHT binding sites. In summary: 4-OHA is a potent and specific inhibitor of aromatase activity in human genital skin fibroblasts, the affinity of the enzyme for 4-OHA being greater than its affinity for the substrate, androstenedione. The influence of 4-OHA on 5 alpha-reductase activity and androgen receptor binding is minimal.
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PMID:The influence of 4-hydroxy-4-androstene-3,17-dione on androgen metabolism and action in cultured human foreskin fibroblasts. 382 Nov 1

The conversion of androstenedione (A) to estrogens, testosterone (T) and 5 alpha-reduced metabolites was studied in different phases of cell growth in 4 lines of cultured human breast carcinoma cells. Aromatase activity was 10-fold greater in MD and DM than in MCF7 cells and was undetectable in ZR75 cells. Estrogen formation in MD and DM lines increased during the phase of exponential growth and decreased to 20% of maximum during confluence. 5 alpha-Reductase activity was determined by the formation of 5 alpha-androstane-3,17-dione (5 alpha-A-dione) and androsterone (AND), and was 5-fold greater in ZR75 cells than MD cells and 2-fold greater than in MCF7 cells. This activity was relatively constant during exponential growth and decreased during confluence. T accumulation was inversely related to 5 alpha-reductase activity. The MCF7 and ZR75 cells which contain estrogen receptors had the highest levels of 5 alpha-reductase activity while the MD line which lacks estrogen receptors had the lowest 5 alpha-reductase activity. The assessment of aromatase and 5 alpha-reductase activity in addition to estrogen and progesterone receptors may be helpful in predicting hormone sensitivity in human breast tumours.
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PMID:The relationship between growth and androstenedione metabolism in four cell lines of human breast carcinoma cells in culture. 386 Apr 51

Androgen receptors and 5 alpha-reductase activity were studied previously in genital skin fibroblasts cultured from normal subjects and patients with abnormalities of sex differentiation. We have now identified and characterized the androgen receptor in cultured human testis fibroblasts (HTF). HTF possess specific receptor proteins for androgens and translocate the receptor-steroid complex to nuclei. Approximately 50% of total cell binding was within nuclei, and 60-70% of nuclear binding was extracted by 0.5 M KCl (1 h; 0 C). Specific binding of dihydrotestosterone (DHT) was absent in HTF cultured from three patients with receptor-negative complete androgen insensitivity. 5 alpha-Reductase activity was very low (less than 100 pg 5 alpha-reduced products/micrograms DNA X h) in HTF after incubation with 200 nM [3H] testosterone (T). Based on this finding, androgen receptor binding of T was studied and resulted in a maximum binding capacity similar to that for DHT, but with a slightly lesser binding affinity (Kd). Binding to the receptor in HTF was specific for androgens (DHT, T, and R1881). [3H]DHT (2 nM) binding in the presence of 100 nM radioinert steroid was decreased by DHT (87%), R1881 (82%), and T (72%), but less with estradiol (53%), progesterone (31%), androstanediol (23%), and dexamethasone (10%). The androgen receptor in HTF was characterized as a macromolecule which sedimented at 4-5S on 0.4 M KCl sucrose density gradients and eluted as three high mol wt peaks on Sephacryl S-300 chromatography. Low but detectable aromatase activity was present in HTF and had the characteristics of being induced by glucocorticoid and having a Km similar to that of aromatase activity for genital skin fibroblasts. In summary, specific androgen receptors are present in HTF, and their characteristics are similar to those previously described for genital skin fibroblasts.
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PMID:Androgen receptor in cultured human testicular fibroblasts. 387 68

Ketoconazole (K) is an antifungal imidazole derivative which has been shown to be a potent inhibitor of testosterone (T) biosynthesis in rodents and humans. To study the effect of K on rat testicular steroidogenesis we measured the activities of five testicular microsomal steroidogenic enzymes in K-treated rats and controls. Thirty male adult rats were given either 2 mg K or water every 12 hours by mouth during 5 days. Mean testicular weight was similar in both groups of animals. The K-treated group had a T serum concentration of 83 +/- 14 ng/dL whereas it was 94 +/- 16 ng/dL in the control group (NS). The K-treated animals had decreased activities of the 3 beta-hydroxysteroid dehydrogenase (830 +/- 48 vs 2,245 +/- 109 pmol/mg protein/min, P less than 0.001), 17-hydroxylase (243 +/- 5 vs 676 +/- 17 pmol/mg protein/min, P less than 0.001), 17-ketosteroid reductase (31 +/- 2 vs 169 +/- 7 pmol/mg protein/min, P less than 0.001), and aromatase enzymes (92 +/- 6 vs 123 +/- 7 pmol/mg protein/min, P less than 0.01). The 17,20-desmolase activity was similar in both groups of animals (210 +/- 4 vs 171 +/- 18 pmol/mg protein/min). We conclude that K given orally to rats inhibits the activity of several testicular steroidogenic enzymes.
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PMID:Effects of ketoconazole on rat testicular steroidogenic enzymatic activities. 387 79

The luteinizing hormone releasing hormone analog D-Trp6-Pro9-Net-LHRH (LHRHa) inhibits rat ovarian estradiol secretion. To determine whether LHRHa decreases serum estradiol concentrations solely by inhibiting gonadotropin secretion or, in addition, by influencing directly ovarian estradiol biosynthesis, we examined the effects of LHRHa on the activities of 5 key ovarian steroidogenic enzymes. Fifty hypophysectomized, gonadotropin-treated rats were given either LHRHa (1 microgram/day) or saline sc during 7 days. The LHRHa treated animals exhibited a significant decrease in serum estradiol when compared with the control group (461 +/- 30 vs 31 +/- 5 pg/ml, mean +/- SE, P less than 0.001). The changes in estradiol concentration were associated with decreases in ovarian weight (372 +/- 19 vs 185 +/- 11 mg, P less than 0.001) and in the microsomal enzyme activities of 3 beta-hydroxysteroid dehydrogenase (156 +/- 5 vs 53 +/- 4 nmol/mg prot/min, P less than 0.001), 17 hydroxylase (4.7 +/- 0.8 vs 3.7 +/- 0.7 nmol/mg prot/min, P less than 0.002), 17,20 desmolase (279 +/- 14 vs 50 +/- 7 pmol/mg prot/min, P less than 0.001), 17 keto-steroid reductase (132 +/- 11 vs 6 +/- 1 nmol/mg prot/min, P less than 0.001), and aromatase (19 +/- 1.5 vs 0.9 +/- 0.1 nmol/mg prot/min, P less than 0.001) in LHRHa treated animals. These findings indicate that LHRHa can inhibit directly rat ovarian estradiol biosynthesis.
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PMID:Direct effect of the luteinizing hormone releasing hormone analog D-Trp6-Pro9-Net-LHRH on rat ovarian steroidogenesis. 389 95

Miconazole and clotrimazole, members of a class of imidazole agents which have broad spectrum antimycotic activity, were shown to be potent inhibitors of steroid aromatase activity of human placental microsomes. The I50 values for the inhibition of aromatase activity by miconazole, clotrimazole, ketoconazole, and aminoglutethimide were 0.6, 1.8, 60 and 44 microM respectively. The most effective compound, miconazole, exhibited competitive kinetics with respect to androstenedione, the aromatase substrate. The apparent inhibitory constant (Ki) was 55 nM, under assay conditions where the apparent Km for androstenedione was 220 nM. The inhibition of aromatase activity by miconazole was shown to be reversible by dilution. Miconazole was a relatively poor inhibitor of the cholesterol side chain cleavage activity of a placental mitochondria-enriched fraction, while both clotrimazole and ketoconazole markedly inhibited this mitochondrial monooxygenase activity. Spectrophotometric studies revealed that miconazole bound to the cytochrome P-450 component of the placental microsomal aromatase complex and had negligible effect on NADPH-cytochrome c (P-450) reductase activity. These results strongly support direct interaction of miconazole with microsomal cytochrome P-450 in human placental microsomes with high affinity resulting in the inhibition of aromatase activity.
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PMID:Imidazole antimycotics: inhibitors of steroid aromatase. 392 Oct 30

The cross-reactivity of human placental microsomal NADPH-cytochrome c reductase antiserum, REDFBIV, against the endometrial reductase alone and as a component of the endometrial aromatase was investigated. Human endometrial particulate fractions were incubated with various amounts of REDFBIV for 1 h at 4 degrees C and both enzyme activities were measured at the end of incubation. The extent of inhibition of these endometrial enzymes was compared with the ability of this antiserum to inhibit the placental microsomal reductase and aromatase activities. The antiserum effectively inhibited the activities of both enzymes in both tissues in a dose dependent manner with aromatase activity inhibited to a greater extent than reductase activity. These results indicate the antiserum to the placental microsomal NADPH-cytochrome c reductase component of aromatase recognizes the reductase component of the aromatase enzyme system in endometrium.
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PMID:Inhibition of aromatase and NADPH cytochrome c reductase activities in human endometrium by the human placental NADPH cytochrome c reductase antiserum. 392 69

Human placental NADPH-cytochrome P-450 reductase, obtained by 2',5'-ADP-Sepharose affinity chromatography, was separated into two reductase-active peaks on a Pharmacia Mono-Q column. By this short, two-step chromatographic procedure, the two reductases were obtained in a homogeneous state with high retention of activity and in over 900-fold purification. Aromatase-reconstituting activity was present only in the higher-molecular-weight reductase (79 000 D), not in the smaller, 70 000 D reductase, which turned out to be a proteolysis product of the former. Both proteins were eluted as a single peak in reversed-phase high-performance liquid chromatography on a Protesil-diphenyl column. Similar results were obtained with bovine hepatic NADPH-cytochrome P-450 reductases. On the other hand, starting from a reductase-free preparation, we have obtained by high-performance ion-exchange chromatography and high-performance size-exclusion chromatography, only partial purification of the aromatase cytochrome P-450, which showed the following values: aromatase activity, 3.995 nmol/min/mg protein (60-fold purification); cytochrome P-450 content, 1.376 nmol/mg protein (23-fold purification); molecular weight, 165 000 D (estimated as an aggregate by size-exclusion chromatography). Although complete purification of the aromatase component has yet to be accomplished, our results suggest that high-performance ion-exchange chromatography on a Mono-Q column is very useful for the purification of acidic, membrane-bound enzymes with good retention of activity.
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PMID:Purification of oestrogen synthetase by high-performance liquid chromatography. Two membrane-bound enzymes from the human placenta. 392 64

The present study was designed to determine if stromal cells derived from human breast adipose tissue contain 5 alpha-reductase activity, and to study the effect of 5 alpha-reduced androgens on aromatase activity under basal and cortisol stimulated conditions. Stromal cells were prepared from breast adipose tissue obtained at the time of surgery from four patients. The cells were isolated after collagenase digestion and were cultured in alpha-minimum essential medium with 15% fetal calf serum. Studies were carried out between days 4 and 11 of the third subculture in the presence or absence of cortisol (10(-6) M). Metabolism of androstenedione (A) was studied over a period of 8 h after addition of medium containing 20 X 10(6) dpm (100 pM) [3H]A. The cells metabolized A to estrone (E1), testosterone (T), 5 alpha-androstane 3, 17-dione (5 alpha-A-dione), androsterone (AND), and dihydrotestosterone. On day 7 of culture, product formation expressed as percent conversion of A per 1 X 10(6) cells ranged as follows: E1, 0.02-0.13; T, 0.12-0.36; 5 alpha-A-dione, 2.05-9.91; and a fraction containing AND and dihydrotestosterone, 0.38-0.59. In the presence of cortisol the rate of cell growth was decreased by 25% to 50%. The formation of E1 increased 150- to 1500-fold and AND formation increased 2- to 8-fold. There was no consistent change in the formation of 5 alpha-A-dione and T. The addition of 5 alpha-A-dione (10(-6) M) to the culture medium at the time of assay resulted in greater than 90% inhibition of E1 formation under both basal and cortisol stimulated conditions. The studies indicate that adipose tissue is an important site for the formation of 5 alpha-reduced androgens.
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PMID:The formation of 5 alpha-reduced androgens in stromal cells from human breast adipose tissue. 394 Nov 60


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