Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

The oxidation of GSH coupled to the redox transitions of 1,4-naphthoquinone derivatives during DT-diaphorase catalysis was examined. The quinones studied included 1,4-naphthoquinone and its dimethoxy- and hydroxy derivatives and were selected according to their different ability to undergo nucleophilic addition with GSH and the dual effect of superoxide dismutase on hydroquinone autoxidation. GSH was oxidized to GSSG during the redox transitions of the above quinones, regardless of their substitution pattern. This effect was accompanied by an increase of total O2 consumption, indicating the ability of GSH to support quinone redox cycling. The values for the relationship [O2]consumed/[GSSG]formed were, with every quinone examined, above unity, thus pointing to the occurrence of autoxidation reactions other than those involved during GSSG formation. These results are discussed in terms of the functional group chemistry of the quinones and the thermodynamic properties of the reactions involved in the reduction of the semi- to the hydro-quinone by GSH.
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PMID:Effect of glutathione on the redox transitions of naphthohydroquinone derivatives formed during DT-diaphorase catalysis. 211 28

The level of quinone oxidoreductases (microsomal and cytosolic DT-diaphorase, NADPH-cytochrome P450 reductase and NADH-cytochrome b5 reductase), superoxide dismutase and glutathione-related enzymatic activities in diethylstilbestrol (DES)-induced carcinogenesis in kidney from Syrian golden hamsters are presented. Animals that exhibited two different stages of DES-induced carcinogenesis in kidney--pre- and neoplastic lesions and tumorous lesions (after 6 and 8 months of continuous exposure to DES respectively)--were studied in comparison to kidneys from control animals. A dramatic decrease in microsomal and cytosolic DT-diaphorase activities (13.6 and 37.8% of controls), as well as in glutathione disulphide reductase (39.5%), and less marked in superoxide dismutase (45.6%), NADH cytochrome b5 reductase (61.9%) glutathione transferase (GST) towards 1-chloro-2,4-dinitrobenzene (CDNB) (66.2%) and glutathione peroxidase (GSH-Px) (80%) activities, were observed in kidneys with pre- and neoplastic lesions. NADPH-cytochrome P450 reductase and GST activity towards 4-hydroxy-2,3-trans-nonenal (4-HNE) showed no statistically significant variation at this stage of carcinogenesis. In kidney from animals with tumorous lesions, all the enzymatic activities mentioned above decreased, except for superoxide dismutase, which was increased to 186% of the control activity. GST activity towards 4-HNE again showed no statistically significant variation. These results suggest that if one-electron reduction of diethylstilbestrol-4',4''-quinone (DESQ) occurs, it may play a very important role in the development of DES carcinogenesis (pre- and neoplastic lesions), since at this stage of carcinogenesis the primary defense mechanisms against the oxygen free radicals generated in this way, i.e. SOD activity, is reduced to less than a half of control values. Both cytosolic and microsomal DT-diaphorase activities are unable at this stage of carcinogenesis to promote effectively the two-electron reduction of DESQ, which would avoid the initial formation of superoxide anion. The consequences of these decreases may be an increased steady-state concentration of superoxide anion and hydrogen peroxide, which in the presence of iron might lead to lipid peroxidation. GST activity towards 4-HNE could be responsible for the possible higher steady-state concentration of this lipid peroxidation product during DES treatment. The induction of DT-diaphorase and its protective role in the prevention of the development of pre- and neoplastic lesions in kidney from Syrian golden hamster during DES treatment is also discussed.
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PMID:The levels of quinone reductases, superoxide dismutase and glutathione-related enzymatic activities in diethylstilbestrol-induced carcinogenesis in the kidney of male Syrian golden hamsters. 211 5

Heart lipoamide dehydrogenase (LADH) catalyzed redox-cycling and O2-. production by (5-nitro-2-furfurylidene)amino derivatives using NADH as electron donor. NADH was a much more effective electron donor than NADPH for the nitroreductase activity. O2-. production was demonstrated by cytochrome c reduction, adrenochrome formation and the effect of superoxide dismutase. Under optimum conditions, nitroreductase activity was about 1% of LADH activity. One electron oxygen reduction and NADH oxidation correlated in 2:1 stoichiometry. The nitroreductase kinetics was in accordance with an ordered bi-bi mechanism. Nitrofuran derivatives bearing unsaturated five- or six-membered nitrogen heterocycles were more effective substrates than those bearing other groups, namely nifurtimox, nitrofurazone, nitrofurantoin and 5-nitro-2-furoic acid. Other nitro compounds (chloramphenicol, benznidazole, 2-nitroimidazole and 5-nitroindole) were ineffective. With the triazole, traizine and imidazole nitrofuran derivatives, the nitroreductase pH curve showed a maximum at pH 8.8, different from the pH optimum for the lipoamide reductase and diaphorase activities. Spectroscopic observations demonstrated pH-dependent structural changes in the triazole(I) and triazine derivatives which would affect their behavior as nitroreductase substrates. The nitroreductase activity was inhibited by p-chloromercuribenzoate and enhanced by cadmium and arsenite, whereas the NADH-induced LADH inactivation failed to affect the nitroreductase activity. In the absence of oxygen. LADH catalyzed nitrofuran reduction to products more reduced than the nitroanion, which were not reoxidized by oxygen. The anaerobic nitrofuran reduction was inhibited by cadmium and arsenite. The assayed nitrofuran compounds did not inhibit LADH lipoamide reductase activity, at variance with their action on glutathione reductase (Grinblat et al., Biochem Pharmacol 38: 767-772, 1989).
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PMID:Catalysis of nitrofuran redox-cycling and superoxide anion production by heart lipoamide dehydrogenase. 217 92

Superoxide (.O2-) production by the NADPH oxidase of a membrane fraction derived from rabbit peritoneal neutrophils activated by 4 beta-phorbol 12-myristate 13-acetate (PMA) was studied at 25 degrees C under different conditions, and measured by the superoxide dismutase inhibitable reduction of cytochrome c. Whereas PMA-activated rabbit neutrophils incubated in a glucose-supplemented medium exhibited a substantial rate of production of .O2-, the membranes prepared by sonication of the activated neutrophils were virtually unable to generate .O2- in the presence of NADPH. Instead, they exhibited an NADPH-dependent diaphorase activity, measured by the superoxide-dismutase-insensitive reduction of cytochrome c. Upon addition of arachidonic acid, which is known to elicit oxidase activation, the NADPH diaphorase activity of the rabbit neutrophil membranes vanished and was stoichiometrically replaced by an NADPH oxidase activity. The emerging oxidase activity was fully sensitive to iodonium biphenyl, a potent inhibitor of the respiratory burst, whereas the diaphorase activity was not affected. Addition of 0.1% Triton X-100 or an excess of arachidonic acid, acting as detergent, resulted in the reappearance of the diaphorase activity at the expense of the oxidase activity. These results indicate that the diaphorase-oxidase transition is reversible. When the rabbit neutrophil membranes were supplemented with rabbit neutrophil cytosol, guanosine 5'-[gamma-thio]triphosphate and Mg2+, in addition to arachidonic acid, not only the NADPH diaphorase activity disappeared, but the emerging NADPH oxidase activity was markedly enhanced (about 10 times compared to that of membranes treated with arachidonic acid alone). The diaphorase-oxidase transition was accompanied by a 10-fold increase in the Km for NADPH, suggesting a change of conformation propagated to the NADPH-binding site during the transition. The treatment of PMA-activated rabbit neutrophils with cross-linking reagents, like glutaraldehyde or 1-(3-dimethylaminopropyl)-3-ethyl carbodiimide, prevented the loss of the PMA-elicited oxidase activity upon disruption of the cells by sonication, suggesting that the interactions between the components of the oxidase complex are stabilized by cross-linking.
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PMID:Respiratory burst of rabbit peritoneal neutrophils. Transition from an NADPH diaphorase activity to an .O2(-)-generating oxidase activity. 217 79

Generation of radicals in vivo depends on metabolic activities. The reactions are usually influenced by (i) the presence and concentration of oxygen; (ii) the availability of transition metals (effects of binding and compartimentalization); (iii) the level of reductants and antioxidants (e.g. nutritional effects). The effects of radicals are thought to be due to (i) membrane damage (affecting passive or active transport through altered fluidity/function interrelationships, intercellular messenging through modifications in the synthesis of prostaglandins and leukotrienes); (ii) protein damage (e.g. affecting membrane transporters, channel proteins, receptor or regulatory proteins, immunomodulators); (iii) damage to DNA. Defense mechanisms consist of (i) prevention of the 'spreading' of primary damage by low molecular weight antioxidants (e.g. vitamin E, GSH, vitamin C, beta-carotene, uric acid); (ii) prevention or limitation of 'secondary' damage by enzymes (e.g. GSH-peroxidase, catalase, superoxide dismutase, DT-diaphorase) and/or chelators; (iii) repair processes, e.g. lipid degradation/membrane repair enzymes (phospholipases, peroxidases, some transferases and reductases), protein disposal or repair enzymes (proteases, GSSG-reductase), DNA degradation repair enzymes (exonuclease III, endonucleases III and IV, glycosylases, polymerases). Recent hypotheses on a messenging function of the superoxide anion O2- are discussed and possible implications of cross-reactions between O2- and nitric oxide (endothelium-derived relaxing factor EDRF) are shortly mentioned.
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PMID:Radical reactions in vivo--an overview. 228 Nov 32

Many anticancer drugs exert their cytotoxic effects via formation of oxygen free radicals. Cellular thiols, glutathione (GSH)-dependent enzymes and other redox enzymes are involved in the metabolism of these anticancer drugs and of the oxygen free radicals that may be generated during their metabolism. We quantified these biochemical parameters in cytosol from human ovarian tissues. We compared non-protein thiol levels, GSH transferase, GSH peroxidase, superoxide dismutase, catalase, DT diaphorase and aldehyde dehydrogenase activity in serous ovarian tumors (n = 15), other malignant ovarian tumors (n = 12), benign ovarian tissue (n = 10) and histologically normal ovarian tissue (n = 12). Mean GSH transferase and DT diaphorase activities were similar in serous and other malignant ovarian tumors. GSH transferase activity was decreased in malignant tissues relative to normal and benign tissues. Mean DT diaphorase and superoxide dismutase activities were increased in the malignant tissues, although this was not statistically significant. The mean levels of all enzymes except superoxide dismutase and aldehyde dehydrogenase in benign tissues were fairly similar to the mean levels found in normal tissue samples. Tissues from patients with serous ovarian tumors, who had received cyclophosphamide and cisplatin prior to surgery, also were analyzed (n = 7). Except for aldehyde dehydrogenase, all the parameters measured were decreased in these samples relative to serous tissue from untreated patients. These biochemical analyses may be useful in understanding the mechanisms involved in the response to chemotherapy.
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PMID:Detoxifying enzymes in human ovarian tissues: comparison of normal and tumor tissues and effects of chemotherapy. 239 58

We investigated the expression of the genes for several antioxidant and xenobiotic-detoxifying enzymes in the multidrug-resistant variant of the human breast cancer cell line MCF-7, MCF-7/Dox. MCF-7/Dox is greater than 500-fold resistant to doxorubicin by clonogenic assay. Enzyme activity determinations in the cytoplasmic compartment of MCF-7/Dox revealed a 25-fold increase in glutathione peroxidase level compared to the parent line (mean +/- SD, 10 +/- 2.8 versus 0.4 +/- 0.24 nmol/min/mg; P less than 0.005). The activity of the other major hydrogen peroxide-detoxifying enzyme, catalase, was diminished in MCF-7/Dox (2.0 +/- 0.4 versus 4.8 +/- 1.4 mumol/min/mg; P less than 0.025 compared to MCF-7). Superoxide dismutase activity did not differ between the two cell lines. The specific activity of the xenobiotic-detoxifying enzyme DT-diaphorase was 4-fold lower in MCF-7/Dox compared to MCF-7 (DT-diaphorase, 117 +/- 45 versus 509 +/- 123 nmol/min/mg; P less than 0.005). Daunorubicinol-producing carbonyl reductase activity was equal in the two lines. Northern blot analysis demonstrated a 0.9-kilobase band of glutathione peroxidase mRNA in MCF-7/Dox; no glutathione peroxidase mRNA was detected in MCF-7. A 2.4-kilobase catalase and 0.7- and 1.4-kilobase superoxide dismutase mRNAs were detectable in MCF-7/Dox and MCF-7. When normalized to 28S RNA, no difference in the mRNA levels of catalase and superoxide dismutase in MCF-7/Dox and MCF-7 could be determined. DT-diaphorase mRNAs of 1.4 and 2.7 kilobases were found in both MCF-7/Dox and MCF-7 cells. A 1.2-kilobase mRNA homologous to the putative carbonyl reductase cDNA was also easily detectable in both MCF-7 and MCF-7/Dox. The amount of mRNA for both xenobiotic-detoxifying enzymes was decreased 2- to 4-fold in the doxorubicin-resistant cells. Southern blot analysis of PstI- and MspI-restricted genomic DNA revealed no evidence for amplification or rearrangement of the glutathione peroxidase gene. These results indicate that, in addition to the previously described overexpression of anionic glutathione S-transferase in MCF-7/Dox cells, an augmented glutathione peroxidase mRNA level is the major alteration in antioxidant and xenobiotic-detoxifying enzyme expression that could contribute to doxorubicin insensitivity in these multidrug-resistant breast cancer cells.
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PMID:Antioxidant and xenobiotic-metabolizing enzyme gene expression in doxorubicin-resistant MCF-7 breast cancer cells. 240 12

The O-dealkylation of 7-alkoxyresorufins to the highly fluorescent compound, resorufin (7-hydroxyphenoxazone), provides a rapid, sensitive, and convenient assay of certain forms of liver microsomal cytochrome P450. The results of this study indicate that NADPH-cytochrome P450 reductase catalyzes the reduction of resorufin (and the 7-alkoxyresorufins) to a colorless, nonfluorescent compound(s). The reduction of resorufin by NADPH-cytochrome P450 reductase was supported by NADPH but not NADH, and was not inhibited by dicumarol, which established that the reaction was not catalyzed by contaminating DT-diaphorase (NAD[P]H-quinone oxidoreductase). In addition to the rate of reduction, the extent of reduction of resorufin was dependent on the concentration of NADPH-cytochrome P450 reductase. The maintenance of steady-state levels of reduced resorufin required the continuous oxidation of NADPH, during which molecular O2 was consumed. When NADPH was completely consumed, the spectroscopic and fluorescent properties of resorufin were fully restored. These results indicate that the reduction of resorufin by NADPH-cytochrome P450 reductase initiates a redox cycling reaction. Stoichiometric measurements revealed of 1:1:1 relationship between the amount of NADPH and O2 consumed and the amount of H2O2 formed (measured fluorometrically). The amount of O2 consumed during the redox cycling of resorufin decreased approximately 50% in the presence of catalase, whereas the rate of O2 consumption decreased in the presence of superoxide dismutase. These results suggest that, during the reoxidation of reduced resorufin, O2 is converted to H2O2 via superoxide anion. Experiments with acetylated cytochrome c further implicated superoxide anion as an intermediate in the reduction of O2 to H2O2. However, the ability of reduced resorufin to reduce acetylated cytochrome c directly (i.e., without first reducing O2 to superoxide anion) precluded quantitative measurements of superoxide anion formation. Superoxide dismutase, but not catalase, increased the steady-state level of reduced resorufin and considerably delayed its reoxidation. This indicates that superoxide anion is not only capable of reoxidizing reduced resorufin, but is considerably more effective than molecular O2 in this regard. Overall, these results suggest that NADPH-cytochrome P450 reductase catalyzes the one-electron reduction of resorufin (probably to the corresponding semiquinoneimine radical) which can either undergo a second, one-electron reduction (presumably to the corresponding dihydroquinoneimine) or a one-electron oxidation by reducing molecular O2 to superoxide anion.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Redox cycling of resorufin catalyzed by rat liver microsomal NADPH-cytochrome P450 reductase. 246 38

Antibody-inhibition experiments established that the induction of cytochrome P450c is largely responsible for the marked increase in liver microsomal 7-ethoxyresorufin O-dealkylation in rats treated with 3-methylcholanthrene, whereas the induction of cytochrome P450b and/or P450e is largely responsible for the marked increase in 7-pentoxy- and 7-benzyloxyresorufin O-dealkylation in rats treated with phenobarbital. When reconstituted with NADPH-cytochrome P450 reductase and lipid, purified cytochrome P450c catalyzed the O-dealkylation of 7-ethoxyresorufin at a rate of approximately 30 nmol/nmol P450/min, which far exceeded the rate catalyzed by either purified cytochromes P450b and P450e or microsomal cytochrome P450c. In contrast, purified cytochrome P450b and P450e were poor catalysts of the O-dealkylation of 7-pentoxy- and 7-benzyloxyresorufin. However, purified cytochrome P450b is an excellent catalyst of several other reactions, such as the N-demethylation of benzphetamine, the hydroxylation of testosterone, and the O-dealkylation of 7-ethoxycoumarin. The low rate of 7-pentoxyresorufin O-dealkylation catalyzed by purified cytochrome P450b did not reflect a requirement for cytochrome b5, and could not be ascribed to an artifact of the method used to measure the formation of resourufin. The catalytic activity of purified cytochrome P450b toward 7-pentoxyresorufin was consistently low over a range of substrate and lipid concentrations, and was not stimulated by sodium deoxycholate (which stimulates the N-demethylation of benzphatamine by purified cytochrome P450b). Evidence is presented which indicates that cytochrome P450c catalyzes the O-dealkylation of both the oxidized and reduced forms of 7-ethoxyresorufin, with perhaps a slight preference for the reduced form. In contrast, cytochrome P450b preferentially catalyzes the O-dealkylation of the oxidized form of 7-pentoxyresorufin. Conditions that favored formation of the reduced form of 7-ethoxyresorufin tended to stimulate its O-dealkylation by purified cytochrome P450c, whereas conditions that favored formation of the reduced form of 7-pentoxyresorufin decreased its rate of O-dealkylation by purified cytochrome P450b. Such conditions included a molar excess of NADPH-cytochrome P450 reductase over cytochrome P450, the presence of superoxide dismutase, and the presence of DT-diaphorase (liver cytosol).(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Reduction of 7-alkoxyresorufins by NADPH-cytochrome P450 reductase and its differential effects on their O-dealkylation by rat liver microsomal cytochrome P450. 253 34

Dopamine (DA) is rapidly oxidized by Mn3(+)-pyrophosphate to its cyclized o-quinone (cDAoQ), a reaction which can be prevented by NADH, reduced glutathione (GSH) or ascorbic acid. The oxidation of DA by Mn3+, which appears to be irreversible, results in a decrease in the level of DA, but not in a formation of reactive oxygen species, since oxygen is neither consumed nor required in this reaction. The formation of cDAoQ can initiate the generation of superoxide radicals (O2-.) by reduction-oxidation cycling, i.e. one-electron reduction of the quinone by various NADH- or NADPH-dependent flavoproteins to the semiquinone (QH.), which is readily reoxidized by O2 with the concomitant formation of O2-.. This mechanism is believed to underly the cytotoxicity of many quinones. Two-electron reduction of cDAoQ to the hydroquinone can be catalyzed by the flavoprotein DT diaphorase (NAD(P)H:quinone oxidoreductase). This enzyme efficiently maintains DA quinone in its fully reduced state, although some reoxidation of the hydroquinone (QH2) is observed (QH2 + O2----QH. + O2-. + H+; QH. + O2----Q + O2-.). In the presence of Mn3+, generated from Mn2+ by O2-. (Mn2+ + 2H+ + O2-.----Mn3+ + H2O2) formed during the autoxidation of DA hydroquinone, the rate of autoxidation is increased dramatically as is the formation of H2O2. Furthermore, cDAoQ is no longer fully reduced and the steady-state ratio between the hydroquinone and the quinone is dependent on the amount of DT diaphorase present. The generation of Mn3+ is inhibited by superoxide dismutase (SOD), which catalyzes the disproportionation of O2-. to H2O2 and O2. It is noteworthy that addition of SOD does not only result in a decrease in the amount of H2O2 formed during the regeneration of Mn3+, but, in fact, prevents H2O2 formation. Furthermore, in the presence of this enzyme the consumption of O2 is low, as is the oxidation of NADH, due to autoxidation of the hydroquinone, and the cyclized DA o-quinone is found to be fully reduced. These observations can be explained by the newly-discovered role of SOD as a superoxide:semiquinone (QH.) oxidoreductase catalyzing the following reaction: O2-. + QH. + 2H+----QH2 + O2. Thus, the combination of DT diaphorase and SOD is an efficient system for maintaining cDAoQ in its fully reduced state, a prerequisite for detoxication of the quinone by conjugation with sulfate or glucuronic acid. In addition, only minute amounts of reactive oxygen species will be formed, i.e. by the generation of O2-., which through disproportionation to H2O2 and further reduction by ferrous ions can be converted to the hydroxyl radical (OH.). Absence or low levels of these enzymes may create an oxidative stress on the cell and thereby initiate events leading to cell death.
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PMID:On the mechanism of the Mn3(+)-induced neurotoxicity of dopamine:prevention of quinone-derived oxygen toxicity by DT diaphorase and superoxide dismutase. 255 82


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