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)

1. Dihydrodiol dehydrogenase activities were investigated in rabbit liver. Using a five-step purification scheme, eight isoenzymes of dihydrodiol dehydrogenase with isoelectric points of 5.55-9.3 and promoter molecular masses of 34-35 kDa were purified to apparent homogeneity and designated CF-1 to CF-6, CM-1 and CM-2. 2. CF-1 and CF-2 had near-neutral isoelectric points of 7.4 and 6.8 and molecular masses of about 125 kDa in the native state. Both enzymes readily accepted NAD+ as well as NADP+ as coenzymes, had relatively low Km values of 0.33 mM and 0.47 mM for benzene dihydrodiol and resembled previously described carbonyl reductases in their substrate specificity towards ketones and quinones. 3. CF-5 and CF-6 had acidic isoelectric points of 5.9 and 5.55 and native molecular masses of approximately 60 kDa. They displayed a strong preference for NADP(H) as coenzyme and had high Km and Vmax with benzene dihydrodiol. Since these enzymes reduced p-nitrobenzaldehyde and glucuronic acid efficiently, they appeared to be closely related to aldehyde reductase. 4. CF-4 had a high 3 alpha-hydroxysteroid dehydrogenase activity for the diagnostic substrate androsterone, a moderate activity for other 3 alpha-hydroxysteroids as well as 17 alpha-hydroxysteroids, and relatively low activities for 3 beta-hydroxysteroids and 17 beta-hydroxysteroids. CF-5 and CM-1 had high 17 beta-hydroxysteroid dehydrogenase activity for the diagnostic substrate 5 alpha-dihydrotestosterone, and low to moderate activities for other 17 beta-hydroxysteroids as well as 3 alpha-hydroxysteroids. 5. The isoenzyme CM-2 had an isoelectric point of 9.3 and was a very active quinone reductase with phenanthrene-9,10-quinone as substrate. It was potently inhibited by phenobarbital. 6. We conclude that the dihydrodiol dehydrogenase activities of rabbit liver are associated with aldehyde and carbonyl reductase and with 3 alpha-hydroxysteroid and 17 beta-hydroxysteroid dehydrogenases.
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PMID:Dihydrodiol dehydrogenase activities of rabbit liver are associated with hydroxysteroid dehydrogenases and aldo-keto reductases. 157 98

The toxicity of quinones--including certain chemotherapeutic agents such as doxorubicin--have been related to the enzymatic or nonenzymatic formation of the corresponding semiquinones and their subsequent reaction with molecular oxygen yielding superoxide anion radicals by spontaneous regenerating of the quinones. This semiquinone redox cycling is prevented by the NAD(P)H:quinone reductase (NQR; EC 1.6.99.2) because it mediates a 2-electron reduction which results in the formation of hydroquinones instead of semiquinones. Interestingly, inducers of this enzyme such as butylated hydroxytoluene protect against the severe ulceration of accidental infiltration of doxorubicin into the area around the intravenous infusion. Recently, it has been shown that this highly protective enzyme has a very high basal activity in the epidermis which is in the same range as in the liver. The human gene of the NQR is localized on chromosome 16 and has been cloned recently as well as the gene of the murine liver NQR. We determined NQR in the cytoplasma of murine skin, liver, and human keratinocytes using 2,6-dichlorophenol-indophenol as substrate. In order to characterize this enzyme, induction by polycyclic hydrocarbones and inhibition with several known inhibitors of dihydrodiol dehydrogenase, aldo-keto and carbonyl reductase activities were determined. There was a similar pattern of inhibition of the basal and induced activity in all tissues so far investigated. Pyrazole, progesterone and phenobarbital did not inhibit; however, rutin and indomethacin inhibited dose-dependently. The most potent inhibitor was dicoumarol. These findings suggest that the same enzymatic form is present in liver and skin, and in murine skin and human keratinocytes.
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PMID:Cutaneous NAD(P)H: quinone reductase: a xenobiotica-metabolizing enzyme with potential cancer and oxidation stress-protecting properties. 176 53

The purpose of this study was to characterize the human cutaneous NAD(P)H: quinone reductase (NQR) activity by known inhibitors of different reductases and to compare it with the murine skin and liver NQR activity. This enzyme plays a major role in the defence of cells against oxygen stress because it inhibits the 1-electron reduction of quinones to semiquinones and their subsequent oxidation to quinones termed as quinone redox cycle. It belongs to the aromatic hydrocarbon-responsive (Ah) battery. This gene battery includes Cyp1a1 (cytochrome P-450 IA1), Cyp1a2 (cytochrome P-450 IA2) and Nmo-1 [NAD(P)H: quinone reductase]. In the skin cytochrome P-450 IA1-dependent activity is about 1-5% compared to the corresponding activity in the liver, whereas NQR has the same activity in skin and liver. NQR was determined in the cytoplasm of murine skin, liver, and human keratinocytes using 2,6-dichlorophenolindophenol as the substrate. The Ah-receptor binding compounds, such as coal tar constituents, or 3-methylcholanthrene induce cytochrome P-450-dependent activities such as aryl hydrocarbon hydroxylase or 7-ethoxyresorufin-O-de-ethylase and NQR, whereas butyl hydroxytoluol, which does not bind to the Ah receptor, induces only NQR. For inhibition studies several known inhibitors of dihydrodiol dehydrogenase, aldo-keto and carbonyl reductase activities were used. There was a similar pattern of inhibition of the basal and induced activity in all tissues investigated. Pyrazole, progesterone and phenobarbital did not inhibit, whereas dicoumarol, rutin and indomethacin inhibited NQR activity in murine skin and liver as well as in human keratinocytes.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Induction and inhibition of NAD(P)H: quinone reductase in murine and human skin. 176 30

A novel pathway of polycyclic aromatic hydrocarbon (PAH) metabolism involves the oxidation of non-K-region trans-dihydrodiols by dihydrodiol dehydrogenase (DD) to yield PAH o-quinones whose cytotoxicity and genotoxicity are unknown. The cytotoxicity of several PAH o-quinones derived from this reaction [naphthalene-1,2-dione (NPQ), benzo[a]pyrene-7,8-dione (BPQ), and 7,12-dimethylbenz[a]anthracene-3,4-dione (DMBAQ)] was examined in rat (H-4IIe) and human (Hep-G2) hepatoma cells which are known to express DD. 2-Methylnaphthalene-1,4-dione (menadione), a known cytotoxic p-quinone, was used as a positive control. Hepatoma cells (1 x 10(6) cells/mL) were exposed to PAH o-quinones (1-100 microM) for 0-4 h, and cell viability and survival were measured and related to O2.- production and changes in redox potential [GSSG/GSH and NAD(P)+/NAD(P)H]. Three different modes of cytotoxicity were observed: (1) NPQ (no bay region) and DMBAQ (methylated bay region) were as cytotoxic as menadione in reducing cell survival but had less effect on cell viability. These o-quinones adversely affected GSH levels and the redox state of the cell and caused an increase in the production of O2.- in cell suspensions. This cytotoxicity was not enhanced by dicoumarol (10 microM), a DT-diaphorase inhibitor, implying that this enzyme is unable to prevent these PAH o-quinones from entering one-electron redox-cycles. (2) BPQ (bay region only) was the least cytotoxic of the PAH o-quinones studied. BPQ decreased cell viability (< 40% at 20 microM) but did not adversely affect cell survival or the redox state of the cell.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Cytotoxicity of polycyclic aromatic hydrocarbon o-quinones in rat and human hepatoma cells. 768 7

The overexpression and purification of recombinant rat liver 3 alpha-hydroxysteroid/dihydrodiol dehydrogenase (3 alpha-HSD; EC 1.1.1.50) in Escherichia coli are described. The properties of the homogeneous recombinant 3 alpha-HSD (r3 alpha-HSD) confirm that a single polypeptide can function as a HSD, as a dihydrodiol dehydrogenase, and as an aromatic aldehyde, ketone, and quinone reductase. Cys-170, Cys-242, and Cys-217, implicated by bromoacetoxysteroid affinity-labeling agents as points of contact for the C-3, C-11, and C-17 positions of steroid ligands, were mutated to alanines. Unexpectedly, the homogeneous C170A and C242A mutants were kinetically similar to wild-type r3 alpha-HSD. By contrast, the C217A mutant gave Km values that were 4-fold higher for androstanedione and 2-fold higher for NADH. Inspection of the recently solved crystal structure of rat liver 3 alpha-HSD (Hoog, S. S., Pawlowski, J. E., Alzari, P. M., Penning, T. M., and Lewis, M. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 2517-2521) places Cys-170 and Cys-242 on the periphery of an alpha/beta-barrel so that they cannot be involved in catalysis of steroid recognition. This demonstrates that bromoacetoxysteroid affinity-labeling agents may provide misleading information regarding the topography of steroid hormone binding sites. When NADPH was modeled into the crystal structure of 3 alpha-HSD, Tyr-55 was implicated as the general acid, since it is in close proximity to the C-4 position of the nicotinamide ring and could polarize the substrate carbonyl. In support of this model, the purified Y55F mutant was found to be catalytically inactive, but still formed an E-NADPH complex (measured by fluorescence titration) and an E-NADH-testosterone complex (measured by equilibrium dialysis). The ability of the Y55F mutant to form binary and ternary complexes, but not aid in hydride transfer, is consistent with Tyr-55 acting as the general acid. 3 alpha-HSD is a member of the aldo-keto reductase superfamily, and Tyr-55 is invariant in members of this family where it may perform a similar function. Tyr-205 is present in a pentapeptide sequence that is conserved in HSDs that belong to the short-chain alcohol dehydrogenase family and has been implicated as the general acid within these enzymes. The Y205F mutant was found to be kinetically similar to wild-type r3 alpha-HSD.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Overexpression and mutagenesis of the cDNA for rat liver 3 alpha-hydroxysteroid/dihydrodiol dehydrogenase. Role of cysteines and tyrosines in catalysis. 817 84

Maintenance of cellular homeostasis is a critical survival trait in tumors when exposed to anticancer drugs. Because conjugation and elimination of drugs and their metabolites is dependent upon sequential and coordinated pathways, acquired drug resistance through a gradual adaptive response would rarely be expected to be the consequence of changes in the expression of one gene product. We have used a number of drug-resistant human cell lines to characterize those genes that are implicated in maintaining a resistant phenotype. Human HT29 colon cancer cells chronically exposed to ethacrynic acid (EA) [a glutathione (GSH) and glutathione S-transferase (GST) modulator] have acquired resistance to the drug. Commensurate with resistance, EA is more effectively conjugated to GSH and effluxed from the resistant cells. Using directed and random (differential display) approaches, a number of detoxification and/or protective gene products have been shown to be expressed at elevated levels. These include: gamma-glutamyl cysteine synthetase (gamma-GCS, the rate-limiting enzyme in GSH biosynthesis); GST pi (the enzyme catalyzing the conjugation reaction); multidrug resistance associated protein (MRP) (the membrane pump responsible for effluxing the conjugate from the cell interior). In addition, other gene products not directly linked with EA metabolism were induced, including dihydrodiol dehydrogenase (an alpha-ketoreductase) (30-fold), DT-diaphorase (threefold), and a transcriptional regulator SSP 3521 (threefold). HL60 cells resistant to a GSH paralog Ter199 also show increased expression of some of these gene products. Furthermore, an adriamycin-resistant human HL60 cell line also shows overexpression of GST pi, gamma-GCS, and MRP, but in addition has approximately 20-fold more DNA-dependent protein kinase catalytic subunit (DNA-PKcs). This enzyme is an early stress response gene that can phosphorylate and activate downstream transcription factors. Such overexpression could impact on the transcriptional control of the other detoxification gene products. Both adriamycin and a typical drug-GSH conjugate (APA-SG) are inhibitors of DNA-PK. Because cellular levels of these conjugates would presumably be a good indicator of stress, it would seem reasonable to speculate that DNA-PK may act as a receiver and transmitter of signals that are crucial to the drug-resistant phenotype. Additionally, this enzyme may prove to be a potentially important target for drug design based upon the inhibitory activity of GSH conjugates.
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PMID:Importance of glutathione and associated enzymes in drug response. 940 35

Induction of Phase 2 enzymes is an effective and sufficient strategy for achieving protection against the toxic and neoplastic effects of many carcinogens. It is proposed that the concept of Phase 2 enzymes as being responsible only for the conjugation of functionalized xenobiotics with endogenous cellular ligands such as glutathione (glutathione S-transferases) and glucuronic acid (UDP-glucuronosyltransferases) be expanded to include proteins with the following common characteristics: (a) coordinate induction by a broad range of chemical agents that all have the capacity to react with sulfhydryl groups; (b) possible regulation by common promoter elements; and (c) catalysis of reactions that lead to comprehensive protection against electrophile and reactive oxygen toxicities, by a wide variety of mechanisms. These mechanisms include: conjugation with endogenous ligands, chemical modification of reactive features of molecules that can damage DNA and other macromolecules, and generation or augementation of cellular antioxidants. In addition to the above conjugating enzymes, a provisional and partial list of Phase 2 proteins might include: NAD(P)H:quinone reductase, epoxide hydrolase, dihydrodiol dehydrogenase, gamma-glutamylcysteine synthetase, heme oxygenase-1, leukotriene B4 dehydrogenase, aflatoxin B1 dehydrogenase, and ferritin.
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PMID:Chemoprotection against cancer by induction of phase 2 enzymes. 1121 5

Polycyclic aromatic hydrocarbons (PAHs) are suspect human lung carcinogens and can be metabolically activated to remote quinones, for example, benzo[a]pyrene-1,6-dione (B[a]P-1,6-dione) and B[a]P-3,6-dione by the action of either P450 monooxygenase or peroxidases, and to non-K region o-quinones, for example B[a]P-7,8-dione, by the action of aldo keto reductases (AKRs). B[a]P-7,8-dione also structurally resembles 4-hydroxyequilenin o-quinone. These three classes of quinones can redox cycle, generate reactive oxygen species (ROS), and produce the mutagenic lesion 8-oxo-dGuo and may contribute to PAH- and estrogen-induced carcinogenesis. We compared the ability of a complete panel of human recombinant AKRs to catalyze the reduction of PAH o-quinones in the phenanthrene, chrysene, pyrene, and anthracene series. The specific activities for NADPH-dependent quinone reduction were often 100-1000 times greater than the ability of the same AKR isoform to oxidize the cognate PAH-trans-dihydrodiol. However, the AKR with the highest quinone reductase activity for a particular PAH o-quinone was not always identical to the AKR isoform with the highest dihydrodiol dehydrogenase activity for the respective PAH-trans-dihydrodiol. Discrete AKRs also catalyzed the reduction of B[a]P-1,6-dione, B[a]P-3,6-dione, and 4-hydroxyequilenin o-quinone. Concurrent measurements of oxygen consumption, superoxide anion, and hydrogen peroxide formation established that ROS were produced as a result of the redox cycling. When compared with human recombinant NAD(P)H:quinone oxidoreductase (NQO1) and carbonyl reductases (CBR1 and CBR3), NQO1 was a superior catalyst of these reactions followed by AKRs and last CBR1 and CBR3. In A549 cells, two-electron reduction of PAH o-quinones causes intracellular ROS formation. ROS formation was unaffected by the addition of dicumarol, suggesting that NQO1 is not responsible for the two-electron reduction observed and does not offer protection against ROS formation from PAH o-quinones.
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PMID:Specificity of human aldo-keto reductases, NAD(P)H:quinone oxidoreductase, and carbonyl reductases to redox-cycle polycyclic aromatic hydrocarbon diones and 4-hydroxyequilenin-o-quinone. 2191 Apr 79