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)

Monodehydroascorbate reductase (EC 1.6.5.4) was purified from cucumber fruit to a homogeneous state as judged by polyacrylamide gel electrophoresis. The cucumber monodehydroascorbate reductase was a monomer with a molecular weight of 47,000. It contained 1 mol of FAD/mol of enzyme which was reduced by NAD(P)H and reoxidized by monodehydroascorbate. The enzyme had an exposed thiol group whose blockage with thiol reagents inhibited the electron transfer from NAD(P)H to the enzyme FAD. Both NADH and NADPH served as electron donors with Km values of 4.6 and 23 microM, respectively, and Vmax of 200 mol of NADH and 150 mol of NADPH oxidized mol of enzyme-1 s-1. The Km for monodehydroascorbate was 1.4 microM. The amino acid composition of the enzyme is presented. In addition to monodehydroascorbate, the enzyme catalyzed the reduction of ferricyanide and 2,6-dichloroindophenol but showed little reactivity with calf liver cytochrome b5 and horse heart cytochrome c. The kinetic data suggested a ping-pong mechanism for the monodehydroascorbate reductase-catalyzed reaction. Cucumber monodehydroascorbate reductase occurs in soluble form and can be distinguished from NADPH dehydrogenase, NADH dehydrogenase, DT diaphorase, microsome-bound NADH-cytochrome b5 reductase, and NADPH-cytochrome c reductase by its molecular weight, amino acid composition, and specificity of electron acceptors and donors.
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PMID:Monodehydroascorbate reductase from cucumber is a flavin adenine dinucleotide enzyme. 405 27

Human placenta contains a thermostable, cytosolic NADH-diaphorase which is different from the other diaphorases and which we designate as diaphorase P. It is specific for NADH and reduces artificial substrates such as dichlorophenol and tetrazolium derivatives, but not natural substrates such as methemoglobin, cytochrome b5 or lipoate. It is antigenically distinct from the ubiquitous red-cell type NADH-diaphorase (soluble cytochrome b5 reductase) specified by the DIA1 locus. Using electrophoretic and immunologic methods, it was possible to detect diaphorase P in various fetal tissues (brain, liver, kidney, muscle), whereas was not found in adult tissues with the exception of the brain. This enzyme, the physiological role of which remains unknown, appears to belong, therefore, to the category of fetal proteins. Its resurgance in primary liver cancer was demonstrated in three cases.
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PMID:Diaphorase P: a new fetal isozyme identified in human placenta. 624 54

Changes in hepatic drug-metabolizing enzymes after intraperitoneal treatment of rats with 2-acetylaminofluorene have been investigated. This treatment was found to increase microsomal epoxide hydrolase to 762%, cytochrome P-450 to 143%, NADPH-cytochrome c reductase to 160%, cytochrome b5 to 171%, cytoplasmic DT-diaphorase to 229% and soluble glutathione S-transferase activities to 200-250% of control values. These increases were time- and dose-dependent, being maximal after injection of 50 mg 2-acetylaminofluorene/kg body wt. once daily for 5 days. Enzyme markers for the plasma membrane, mitochondria, lysosomes and the soluble cytoplasm were not affected by treatment with 2-acetylaminofluorene. The present study indicates that this induction is different from that obtained with phenobarbital and 3-methylcholanthrene and more closely resembles that seen with trans-stilbene oxide.
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PMID:Characterization of the induction of drug-metabolizing enzymes by 2-acetylaminofluorene. 722 16

We have previously shown that oleanolic acid (OA) protects mice against the hepatotoxicity of carbon tetrachloride, acetaminophen, bromobenzene, thioacetamide, furosemide, phalloidin, colchicine, cadmium, D-galactosamine and endotoxin. This study was designed to examine whether OA modulates hepatic toxicant-activating and detoxifying systems as a means of protection. Mice were treated with OA (100 and 200 mumol/kg s.c.) for 3 days, and liver microsomes and cytosols were prepared 24 hr after the last dose. OA produced a dose-dependent reduction in liver microsomal cytochrome P450 (P450) levels (25-37%) and cytochrome b5 (15-21%) content, but had no effect on NADPH-cytochrome c reductase activity. OA treatment also decreased several P450 enzyme activities, such as coumarin 7-hydroxylation (45%), 7-pentoxyresorufin O-dealkylation (35%), 7-ethoxyresorufin O-dealkylation (25%) and chlorzoxazone 6-hydroxylation (20%). Treatment of mice with OA decreased caffeine N3-demethylation (40%), but had no effect on caffeine 8-hydroxylation. OA treatment decreased testosterone 6 alpha- and 15 alpha-hydroxylation (40-50%) and androstenedione formation (35%), but slightly increased testosterone 1 alpha/beta-, 2 beta- and 6 beta-hydroxylation. Consistent with enzyme activities, OA decreased the amounts of mouse liver CYP1A and CYP2A enzymes, but had no appreciable effect on CYP3A enzymes, as determined by immunoblotting with antibodies against rat P450 enzymes. OA treatment slightly increased liver glutathione (GSH) content and the activity of GSH S-transferases toward 1-chloro-2,4-dinitrobenzene, but had no effect on GSH peroxidase and GSH reductase. The activities of superoxide dismutase and DT-diaphorase were unaffected by OA treatment. At the high dose of OA, catalase activity was decreased by 20%.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effect of oleanolic acid on hepatic toxicant-activating and detoxifying systems in mice. 747 65

Aerobic sensitivity to indoloquinone EO9 has been shown to correlate with cellular levels of the two-electron reducing enzyme DT-diaphorase. However, little is known about the relative roles of one- and two-electron reducing enzymes in the hypoxic cytotoxicity of EO9. We have characterised a panel of 23 human tumour cell lines for both bioreductive enzyme activities and aerobic sensitivity to EO9. Eight cell lines were then selected for a comparison of aerobic and hypoxic sensitivities. Activities of DT-diaphorase showed a wide range (> 10,000-fold), while activities of the one-electron reducing cytochrome b5 and cytochrome P450 reductases were generally lower and showed only a 15- and 25-fold range respectively. The aerobic cytotoxicity of EO9 was clearly related to the cellular levels of DT-diaphorase (r = 0.87), with higher levels giving increased sensitivity, but not to the levels of one-electron reducing enzymes. In contrast, there was no relationship between sensitivity to BCNU, cisplatin or the bioreductive agent SR 4233 (tirapazamine) and activities of any of these reducing enzymes. Under hypoxic conditions sensitivity to EO9 was markedly increased in cell lines with low levels of DT-diaphorase activity, while cell lines with high levels show only a small increase in sensitivity. This is reflected by a clear correlation (r = 0.98) between cellular DT-diaphorase activity and the ratio of aerobic to hypoxic sensitivity to EO9. However, we have now for the first time demonstrated an inverse correlation (r = 0.93) between the cellular activity of DT-diaphorase and hypoxic sensitivity to EO9, that is sensitivity decreases with increasing DT-diaphorase activity. Moreover, this correlation was lost when cells were exposed to drug in the presence of dicoumarol, supporting an involvement of DT-diaphorase in this relationship. These observations question the previously straightforward role for DT-diaphorase in the metabolic activation of EO9. Whereas DT-diaphorase is associated with increased toxicity in air, it appears to reduce the cytotoxicity of EO9 in hypoxic conditions. This suggests either that the one-electron reduction product of EO9 metabolism, the semiquinone, is more toxic than the two-electron reduction product, the hydroquinone, or that the hydroquinone is not cytotoxic and aerobic toxicity is due to the transient appearance of the semiquinone upon back oxidation of the hydroquinone.
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PMID:DT-diaphorase protects cells from the hypoxic cytotoxicity of indoloquinone EO9. 752 85

One mechanism by which chemicals cause cellular injury is the formation of reactive oxygen species. In vitro studies have shown that metallothionein (MT), a small metal-binding, sulfhydryl-rich, readily inducible protein, can scavenge reactive oxygen species, especially hydroxyl radicals. Nevertheless, whether or not MT protects against oxidative stress in the intact animal is not known. Experimental induction of MT could help to clarify this question, however, it is unclear whether agents that induce MT also influence known antioxidant systems. Therefore, the present study was designed to determine whether the well-known MT inducers are specific for induction of MT or whether they might also influence other hepatic systems that protect against oxidative stress. Male rats were administered cadmium chloride (Cd; 30 mumol/kg, s.c.), zinc chloride (Zn; 1000 mumol/kg, s.c.), alpha-hederin (alpha-H, 30 mumol/kg, s.c.) or lipopolysaccharide (LPS; 1 mg/kg, s.c.) 24 h prior to measurement of antioxidant systems. Zn and alpha-H increased hepatic GSH concentration 20% and 55%, respectively. Cd significantly increased, whereas LPS reduced, the activities of selenium-dependent glutathione peroxidase and glutathione reductase. Glutathione S-transferases were not altered by any of the inducers. Cd also increased DT-diaphorase activity. Cd, Zn and alpha-H all decreased catalase activity 20-35%, while the activity of superoxide dismutase was unaffected by the inducers. The amount of total cytochrome P450 enzymes and cytochrome b5 were decreased by LPS, Cd and alpha-H, while Zn appeared to have no effect. The activities of P450 enzymes towards testosterone oxidation were also decreased by LPS, Cd and alpha-H. In conclusion, all four MT inducers examined affect systems known to protect cells against oxidative stress. Therefore, using these chemicals to determine the in vivo role of MT in protecting against oxidative stress poses difficulties.
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PMID:Effect of several metallothionein inducers on oxidative stress defense mechanisms in rats. 856 Apr 99

Ellagic acid (EA), a naturally occurring plant polyphenol possesses broad chemoprotective properties. Dietary EA has been shown to reduce the incidence of N-2-fluorenylacetamide-induced hepatocarcinogenesis in rats and N-nitrosomethylbenzylamine (NMBA)-induced rat esophageal tumors. In this study changes in the expression and activities of specific rat hepatic and esophageal mucosal cytochromes P450 (P450) and phase II enzymes following dietary EA treatment were investigated. Liver and esophageal mucosal microsomes and cytosol were prepared from three groups of Fisher 344 rats which were fed an AIN-76 diet containing no EA or 0.4 or 4.0 g/kg EA for 23 days. In the liver total P450 content decreased by up to 25% and P450 2E1-catalyzed p-nitrophenol hydroxylation decreased by 15%. No changes were observed in P450 1A1, 2B1 or 3A1/2 expression or activities or cytochrome b5 activity. P450 reductase activity decreased by up to 28%. Microsomal epoxide hydrolase (mEH) expression decreased by up to 85% after EA treatment, but mEH activities did not change. The hepatic phase II enzymes glutathione S-transferase (GST), NAD(P)H:quinone reductase [NAD-(P)H:QR] and UDP glucuronosyltransferase (UDPGT) activities increased by up to 26, 17 and 75% respectively. Assays for specific forms of GST indicated marked increases in the activities of isozymes 2-2 (190%), 4-4 (150%) and 5-5 (82%). In the rat esophageal mucosa only P450 1A1 could be detected by Western blot analysis and androstendione was the only P450 metabolite of testosterone detectable. However, there were no differences in the expression of P450 1A1, the formation of androstendione or NAD(P)H:QR activities between control and EA-fed rats in the esophagus. Although there was no significant decrease in overall GST activity, as measured with 1-chloro-2,4-dinitrobenzene (CDNB), there was a significant decrease in the activity of the 2-2 isozyme (66% of control). In vitro incubations showed that EA at a concentration of 100 microM inhibited P450 2E1, 1A1 and 2B1 activities by 87, 55 and 18% respectively, but did not affect 3A1/2 activity. Using standard steady-state kinetic analyses, EA was shown to be a potent non-competitive inhibitor of both liver microsomal ethoxyresorufin O-deethylase and p-nitrophenol hydroxylase activities, with apparent Ki values of approximately 55 and 14 microM respectively. In conclusion, these results demonstrate that EA causes a decrease in total hepatic P450 with a significant effect on hepatic P450 2E1, increases some hepatic phase II enzyme activities [GST, NAD-(P)H:QR and UDPGT] and decreases hepatic mEH expression. It also inhibits the catalytic activity of some P450 isozymes in vitro. Thus the chemoprotective effect of EA against various chemically induced cancers may involve decreases in the rates of metabolism of these carcinogens by phase I enzymes, due to both direct inhibition of catalytic activity and modulation of gene expression, in addition to effects on the expression of phase II enzymes, thereby enhancing the ability of the target tissues to detoxify the reactive intermediates.
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PMID:The effects of dietary ellagic acid on rat hepatic and esophageal mucosal cytochromes P450 and phase II enzymes. 862 97

The enzymatic features and molecular species of the inhibitory action of menadione on lipid peroxidation in rat liver microsomes were examined. In an ascorbate-supported system or a NADH-supported reconstituted system containing NADH-cytochrome b5 reductase and cytochrome b5, menadione was not an inhibitor of lipid peroxidation at pH 7.5, while some antioxidant ability was observed at lower pH ranges. Lipid peroxidation in the presence of menadione in the NADH-supported reconstituted system at pH 7.5 was markedly inhibited by adding lipoamide dehydrogenase. NAD(P)H-supported lipid peroxidation in microsomes with increased DT-diaphorase activity from 3-methylcholanthrene-treated rats was highly susceptible to menadione. These inhibitions were abolished by dicoumarol, an inhibitor of DT-diaphorase. Cumene hydroperoxide-dependent lipid peroxidation in microsomes, with desferal and NADP+ to prevent nonheme iron-dependent reactions and oxygen radical generation, was inhibited by menadione in the presence of NADPH, and the inhibition was also more effective in the microsomes with increased DT-diaphorase activity. Menadiol reacted with 1,1-diphenyl-2-picrylhydrazyl (DPPH) in ethanol at a molar ratio of DPPH/menadiol at 1.9. In an iron-supported reconstituted enzymatic or a nonenzymatic system at pH 7.5, menadiol showed an antioxidant effect at an early stage, followed by a prooxidant effect, which was prevented by SOD, probably by protecting menadiol autooxidation. These results show that menadione exerts an antioxidant effect through participation of microsomal DT-diaphorase by generating menadiol with a radical scavenging ability, while menadiol also has a prooxidant property.
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PMID:Enzymatic and molecular aspects of the antioxidant effect of menadione in hepatic microsomes. 883 52

Flavin electron transferases can catalyze one- or two-electron reduction of quinones including bioreductive antitumor quinones. The recombinant neuronal nitric oxide synthase (nNOS) reductase domain, which contains the FAD-FMN prosthetic group pair and calmodulin-binding site, catalyzed aerobic NADPH-oxidation in the presence of the model quinone compound menadione (MD), including antitumor mitomycin C (Mit C) and adriamycin (Adr). Calcium/calmodulin (Ca2+/CaM) stimulated the NADPH oxidation of these quinones. The MD-mediated NADPH oxidation was inhibited in the presence of NAD(P)H:quinone oxidoreductase (QR), but Mit C- and Adr-mediated NADPH oxidations were not. In anaerobic conditions, cytochrome b5 as a scavenger for the menasemiquinone radical (MD*-) was stoichiometrically reduced by the nNOS reductase domain in the presence of MD, but not of QR. These results indicate that the nNOS reductase domain can catalyze a only one-electron reduction of bivalent quinones. In the presence or absence of Ca2+/CaM, the semiquinone radical species were major intermediates observed during the oxidation of the reduced enzyme by MD, but the fully reduced flavin species did not significantly accumulate under these conditions. Air-stable semiquinone did not react rapidly with MD, but the fully reduced species of both flavins, FAD and FMN, could donate one electron to MD. The intramolecular electron transfer between the two flavins is the rate-limiting step in the catalytic cycle [H. Matsuda, T. Iyanagi, Biochim. Biophys. Acta 1473 (1999) 345-355). These data suggest that the enzyme functions between the 1e- <==> 3e- level during one-electron reduction of MD, and that the rates of quinone reductions are stimulated by a rapid electron exchange between the two flavins in the presence of Ca2+/CaM.
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PMID:One-electron reduction of quinones by the neuronal nitric-oxide synthase reductase domain. 1092 3

Effect of vanadium on hepatic xenobiotic biotransformation in rats exposed to diethylnitrosamine (DENA, 200 mg/kg body weight, intraperitoneally) was investigated to elucidate a possible mechanism of vanadium mediated prevention of chemical carcinogenesis. Vanadium supplementation (0.5 ppm ad libitum with drinking water), at different phases before and after DENA treatment, significantly modulated the decrease in contents of total cytochrome P-450, cytochrome b5, activity of nicotinamide adenine dinucleotide phosphate (NADPH), (reduced form) cytochrome reductase, and uridine diphospho-glucuronyl transferase (UDPGT) in microsomal fractions of whole liver, hyperplastic nodules (HNs) and non nodular surrounding parenchyma (NNSP) as induced by DENA, 20 weeks following its administration. Supplementary vanadium had also substantial influence on the activities of cytosolic enzymes, like, uridine diphospho (UDP)-glucose dehydrogenase and NAD(P)H: quinone oxidoreductase (DT-diaphorase) in the concerned tissue which were observed to be remarkably decreased as a result of DENA treatment in comparison to that of the control counterparts. However, vanadium was found to have little or no effect on the lowering ofaryl hydrocarbon hydroxylase (AHH) activity by DENA administration. On the basis of significant modulation of DENA induced alterations in cytosolic and microsomal enzyme activity it can be presumed that the chemoprotective effect of vanadium might be mediated through elevation of phase II conjugating enzymes which in turn, lead to a move and shift of metabolic profile that reduces the intracellular concentration of carcinogen derived reactive intermediates.
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PMID:Differential modulation of xenobiotic metabolizing enzymes by vanadium during diethylnitrosamine-induced hepatocarcinogenesis in Sprague-Dawley rats. 1098 72


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