Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.6.5.2 (NQO1)
 6,196 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Carbonyl reductase (NADPH: secondary-alcohol oxidoreductase; EC 1.1.1.184), a widely distributed NADPH-dependent enzyme considered as both an aldo-keto reductase and a quinone reductase, was cloned from a human liver genomic library and transiently expressed in COS7 cells. The gene contains 3142 bases comprising three exons and two introns. The absence of a CAAT and TATA box and the presence of a GC-rich island are characteristic of many "housekeeping" genes. Transient expression of the genomic gene in COS7 cells using an expression vector containing an SV40 origin of replication resulted in a greater than 50-fold increase in both menadione reductase activity and daunorubicin reductase activity, suggesting that both activities are derived from the same enzyme. Carbonyl reductase mRNA levels reflected enzyme activity levels in the transfected cells. Other parameters, such as pH profile, cofactor requirements, substrates, and inhibitors, were similar to those of carbonyl reductase purified by other investigators. Potential regulatory elements with consensus sequences for two GC boxes and the transcriptional activator protein AP-2 were present upstream of the transcriptional start site. Although the precise role of carbonyl reductase is unknown, the enzyme is involved in drug metabolism and in the reduction of activated carbonyl compounds. Its ability to act as a quinone reductase also implies a potential to modulate oxygen free radicals.
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PMID:Genomic sequence and expression of a cloned human carbonyl reductase gene with daunorubicin reductase activity. 192 84

The effect of HgCl2 on human term placental aryl hydrocarbon hydroxylase (AHH), quinone reductase (QR), catecholamine-O-methyltransferase (COMT), and glucose-6-phosphate dehydrogenase (G-6-PD) enzyme activities was studied after incubation of placental explants with the salt for either a 6 or 24 hr period. Mercury (Hg) increased the activities of AHH, QR and COMT, but decreased that of G-6-PD. The increases in enzyme activities, as well as the decrease in G-6-PD activity observed were in all cases time- and dose-dependent. The data suggest that Hg exerts an enhancing effect on the activity of placental phase I enzyme (AHH) and phase II enzymes (QR and COMT). This enhancement may be due to increased de novo synthesis, elimination of some suppressing agent(s), or the decreased breakdown of enzyme protein. Also, the inhibitory effect of Hg on G-6-PD activity appears to indicate that this enzyme is appreciably more sensitive to Hg than the other three enzymes. These findings may imply increased cellular resistance to Hg toxicity. The altered state of activity may also be used as a tool for monitoring exposure to this metal.
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PMID:In vitro effect of mercury on aryl hydrocarbon hydroxylase, quinone reductase, catecholamine-O-methyltransferase and glucose-6-phosphate dehydrogenase activities in term human placenta. 194 76

Indole-3-carbinol (I-3-C) and 5,10-dihydroindeno[1,2-b]indole (DHII) have been shown to be protective against carbon tetrachloride and other chemicals that cause hepatic toxicity. In part, this protection appears to be afforded by the ability of these compounds to act as antioxidants, with DHII having much the greater efficacy. In order to understand the mechanisms of chemoprotection, as well as the potential for therapeutic and pharmaceutical use in humans, the antioxidants I-3-C and DHII were examined for their intrinsic acute toxicity, and their hepatic enzyme inducing properties in mice. The results were compared with those of the well characterized agent phenobarbital. Following treatment by gavage for 10 days with 50 mg compound/kg body weight, I-3-C produced modest (10-50%) increases in hepatic cytochrome P-450, aminopyrine N-demethylase, UDP-glucuronosyl transferase (UDPGT) and glutathione S-transferase (GST), and a four-fold increase in NAD(P)H: (quinone acceptor) oxidoreductase (quinone reductase) activity. DHII did not alter oxidative enzyme activities, but increased GST and UDPGT by about 50%, and quinone reductase over five-fold. In the acute toxicity studies, DHII produced no observable 24-hr acute toxicity up to 4 g/kg body weight, except for a slight decrease in haematocrit. However, I-3-C exhibited a dose-dependent toxicity above 100 mg/kg body weight, including a decrease in hepatic reduced glutathione after 2 hr and severe neurological toxicity, and the release of liver enzymes to the plasma at 24 hr. We conclude, on the basis of the superior antioxidation efficacy of DHII, its enzyme-inducing properties, and intrinsic toxicity, that DHII or cogeners thereof have great potential as chemoprotective or therapeutic agents. However, I-3-C does not have such potential.
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PMID:Intrinsic acute toxicity and hepatic enzyme inducing properties of the chemoprotectants indole-3-carbinol and 5,10-dihydroindeno[1,2-b]indole in mice. 204 Apr 85

The effect of dietary intake of butylated hydroxytoluene (BHT) (0.6%) on the in vivo distribution, metabolism and DNA-binding of intragastrically administered 7,12-dimethylbenz[a]anthracene (DMBA) was evaluated. Urinary excretion of DMBA increased, blood content of metabolized DMBA increased and blood content of non-metabolized DMBA decreased for rats fed the diet containing BHT as compared to rats fed the control diet. The binding of DMBA to both liver and mammary DNA decreased for rats fed the diet containing BHT as compared to controls. The liver activities of glutathione-S-transferase (GST), epoxide hydrolase (EH) and NAD(P)H-quinone reductase (QR) increased in response to BHT feeding. However, no increase in the mammary tissue activities of these enzymes was observed. These results suggest that the ability of dietary BHT to inhibit the initiation of DMBA-induced mammary carcinogenesis partly may be due to decreased binding of DMBA to mammary DNA. This effect of BHT is not due to an increase in mammary tissue activities of GST, EH and QR, enzymes involved in carcinogen detoxification, but may involve increased liver metabolism of DMBA to products that do not bind to DNA.
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PMID:Effect of dietary butylated hydroxytoluene on the in vivo distribution, metabolism and DNA-binding of 7,12-dimethylbenz[a]anthracene. 210 65

The present study is part of an effort to identify biomarkers for various stages of preneoplasia. For this purpose, quinone reductase [NAD(P)H:quinone oxidoreductase, EC 1.6.99.2] (QR) activity in the forestomach of ICR/Ha mice was investigated at successive time points during benzo(a)pyrene (BP)-induced carcinogenesis. Six mg of BP in 0.2 ml of cottonseed oil or cottonseed oil alone were given orally twice a week for 2 weeks to female ICR/Ha mice. Ten mice from each group were sacrificed sequentially at 2-week intervals, and the QR activity was determined in the forestomach, a target tissue for BP carcinogenicity, and also in the glandular stomach, a non-target tissue. QR was significantly increased in the cytosolic, microsomal, and mitochondrial fractions of the forestomach of BP-treated animals. There was no significant increase in this activity in any fraction of the glandular stomach. The increases in QR activity in the subcellular fractions of the forestomach from BP-treated animals showed a two-surge pattern. The first was manifested at 2 weeks. The second, found at week 6, continued throughout the remaining course of the experiment. To our knowledge, the time course of changes in QR activity in the three subcellular fractions of mouse forestomach during BP carcinogenesis has not been demonstrated previously.
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PMID:Long term effects of benzo(a)pyrene on the activity of NAD(P)H:quinone reductase in the forestomach and glandular stomach of ICR/Ha mice. 210 67

It was found that when Escherichia coli is grown in the presence of 0.2-0.3 mM menadione (2-methyl-1,4-naphthoquinone), an FMN-dependent NADH-quinone reductase increases more than 20-fold in the cytoplasmic fraction. The menadione-induced quinone reductase was isolated from the cytoplasmic fraction of induced cells. The purified enzyme had an Mr of 24 kDa on SDS-polyacrylamide gel electrophoresis. The enzyme required flavin as a cofactor and a half-maximum activity was obtained with 0.54 microM FMN or 16.5 microM FAD. The enzyme had a broad pH optimum at pH 7.0-8.0 and reacted with NADH, but not with NADPH. The reaction followed a ping-pong mechanism and the intrinsic Km values for NADH and menadione were estimated to be 132 microM and 2.0 microM, respectively. Dicoumarol was a simple competitive inhibitor with respect to NADH with a Ki value of 0.22 microM. The electron acceptor specificity of this enzyme was very similar to that of NAD(P)H: (quinone acceptor) oxidoreductase (EC 1.6.99.2, DT-diaphorase) from rat liver. Since menadione is reduced by the two-electron reduction pathway to menadiol, the induction of this enzyme is likely to be an adaptive response of E. coli to partially alleviate the toxicity of menadione.
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PMID:Characterization of FMN-dependent NADH-quinone reductase induced by menadione in Escherichia coli. 211 86

Dimethyl fumarate and dimethyl maleate are potent inducers of cytosolic NAD(P)H:(quinone acceptor) oxidoreductase (here designated quinone reductase) activity in Hepa 1c1c7 murine hepatoma cells in culture, whereas fumaric and maleic acids are much less potent, in agreement with the much greater reactivity of the esters as Michael reaction acceptors (P. Talalay, M. J. De Long, and H. J. Prochaska, Proc. Natl. Acad. Sci. USA, 85:8261-8265, 1988). Dimethyl fumarate also induced quinone reductase in mutants of the Hepa 1c1c7 cell line that were either defective in the Ah receptor or in cytochrome P1-450 activity, thereby establishing that this compound is a monofunctional inducer (H. J. Prochaska and P. Talalay, Cancer Res., 48: 4776-4782, 1988). Addition of dimethyl fumarate to the diet of female CD-1 mice and female Sprague-Dawley rats at 0.2-0.5% concentrations elevated cytosolic glutathione transferases and quinone reductase activities in a variety of organs, whereas much higher concentrations of fumaric acid were only marginally active. The widespread induction of such detoxication enzymes by dimethyl fumarate suggests the potential value of this compound as a protective agent against chemical carcinogenesis and other forms of electrophile toxicity. This proposal is supported by the finding that the concentrations of dimethyl fumarate required to obtain substantial enzyme inductions were well tolerated by rodents. Furthermore, the parent fumaric acid has low chronic toxicity and is a naturally occurring metabolic intermediate that is already in the food chain as an additive, and fumarate salts and esters are used for therapeutic purposes in man.
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PMID:Induction of glutathione transferases and NAD(P)H:quinone reductase by fumaric acid derivatives in rodent cells and tissues. 212 43

DT-diaphorase [NAD(P)H dehydrogenase (quinone), EC 1.6.99.2] is a flavoprotein enzyme widely distributed in the cytosolic fractions of various animal tissues. It is also called menadione reductase or NAD(P)H-quinone reductase and catalyzes NAD(P)H-dependent 1-, 2- or 4-electron reduction of certain redox dyes, aromatic nitro compounds, aromatic C-nitroso compounds and probably azo-dyes, as well as menadione (vitamin K3) and other quinones. Dicumarol exerts characteristic inhibition on DT-diaphorase, whereas serum albumin and certain non-ionic detergents exert activation. Excessive concentrations of many of the electron acceptors inhibit the activity of this enzyme. The physiological significance of DT-diaphorase is still obscure because the physiological vitamins (K1 and K2) and coenzyme Q10 are difficult to reduce with this enzyme. Results of recent studies suggest that DT-diaphorase prevents formation of active oxygen species. Activities in liver and other tissues are known to be enhanced by administration of chemicals including certain carcinogens such as 3-methylcholanthrene (3-MC), anti-oxidants such as 3-tert-butyl-4-hydroxyanisole (BHA), and other compounds. Both basal and induced activities vary considerably with tissue, sex, strain and species of animals. The strain variations in activities in rat and mouse liver are known to be inherited, and the trait of hereditary transmission can be adequately explained by postulating two loci of genes or gene clusters regulating the activity. Resistance of animals to various toxic or carcinogenic substances may be promoted by BHA administration and depressed by dicumarol administration. Thus, attention has been focused on the role played by DT-diaphorase in the detoxication of foreign compounds. Knowledge on strain variations in basal and induced activities of tissue DT-diaphorase is of potential value when choosing a rat or mouse strain suitable for studying the toxic effects of drugs, especially drugs expected to be detoxified by reductive metabolism. With future progress in research on DT-diaphorase, this enzyme might be applied to prophylactic and therapeutic medicine.
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PMID:Advances in research on DT-diaphorase--catalytic properties, regulation of activity and significance in the detoxication of foreign compounds. 212 71

Most chemical carcinogens require activation to reactive electrophilic forms by Phase 1 enzymes (cytochromes P-450) in order to exert their toxic and neoplastic effects. The resultant electrophiles are susceptible to metabolic conjugation and other types of detoxications by Phase 2 enzymes (glutathione transferases, NAD(P)H: quinone reductase, glucuronosyltransferases). The balance between Phase 1 and Phase 2 enzymes is an important determinant of whether exposure to carcinogens will result in toxicity and neoplasia. Measurements of the activity of quinone reductase (QR) provide an efficient method for studying the potency and mechanism of Phase 2 enzyme induction. QR can be measured easily in murine hepatoma cells (Hepa lclc7) grown in microtiter plate wells, and the inductive response of these cells closely parallels the behavior of rodent tissues in vivo. Some inducers (such as large planar aromatics) are bifunctional; they induce both Phase 1 and Phase 2 enzymes and require binding to the Ah receptor and enhanced transcription of the cytochrome P1-450 system. Other inducers (e.g., phenolic antioxidants, 1, 2-dithiole-3-thiones, coumarins, thiocarbamates) are monofunctional and are independent of Ah receptor function. Monofunctional enzyme induction protects against carcinogens. The induction of Phase 2 enzymes by monofunctional inducers depends on the presence, or acquisition by metabolism, of electrophilic centers, and many of these inducers are Michael reaction acceptors. Our search for chemoprotective enzyme inducers for potential use as chemoprotectors in man is currently focused on fumarate derivatives, as well as on the identification of other monofunctional inducers in extracts of vegetables.
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PMID:Regulation of enzymes that detoxify the electrophilic forms of chemical carcinogens. 213 77

Rat liver NAD(P)H:quinone oxidoreductase cDNA was cloned and expressed in a eukaryotic cell expression plasmid containing a cytomegalovirus (CMV) promoter. Transient expression of enzyme activity and RNA transcription were measured in COS7 cells. The expressed quinone reductase has kinetic properties similar to the rat liver enzyme and is inhibited by dicourmarol, a known inhibitor of NAD(P)H:quinone oxidoreductase. Site-directed mutagenesis experiments carried out using this expression system revealed possible regions involved in NAD(P)H binding.
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PMID:Rat liver NAD(P)H:quinone oxidoreductase: cDNA expression and site-directed mutagenesis. 214 79


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