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)

Extracts of E. coli contain at least three easily separable NAD(P)H:paraquat diaphorases. One of these is identified as thioredoxin reductase, which accounts for most of the PQ++ diaphorase in a thioredoxin reductase overproducer but is only 25% of this activity in a wild type. NADP+, but not NAD+, inhibited the diaphorase activity of thioredoxin reductase. All of the soluble PQ++ diaphorases of E. coli are stable during fractionation by HPLC and none depend upon the cooperative action of components separable by this technique. GSSG reductase is inhibited by PQ++ and is not, to any significant degree, a contributor to the diaphorase activity of E. coli.
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PMID:Paraquat diaphorases in Escherichia coli. 802 98

In view of the ubiquitous role of the thioredoxin/thioredoxin reductase (TRX/TR) system in living cells, the interaction of Arabidopsis thaliana NADPH-thioredoxin reductase (EC 1.6.4.5) with quinones, an important class of redox cycling and alkylating xenobiotics, was studied. The steady-state reactions of A. thaliana TR with thioredoxin (TRX) and reaction product NADP+ inhibition patterns were in agreement with a proposed model of E. coli enzyme (B.W. Lennon, C.H. Williams, Jr., Biochemistry, vol. 35 (1996), pp. 4704-4712), that involved enzyme cycling between four- and two-electron reduced forms with FAD being reduced. Quinone reduction by TR proceeded via a mixed single- and two-electron transfer, the percentage of single-electron flux being equal to 12-16%. Bimolecular rate constants of quinone reduction (kcat/km) and reaction catalytic constants (kcat) increased upon an increase in quinone single-electron reduction potential. E(1)7. In several cases, the kcat of quinone reduction exceeded kcat of TRX reduction, suggesting that quinones intercepted electron flux from TR to TRX. Incubation of reduced TR with alkylating quinones resulted in a rapid loss of TRX-reductase activity, while quinone reduction rate was unchanged. In TRX-reductase and quinone reductase reactions of TR, NADP+ exhibited different inhibition patterns. These data point out that FAD and not the catalytic disulfide of TR is responsible for quinone reduction, and that quinones may oxidize FADH2 before it reduces catalytic disulfide. Most probably, quinones may oxidize the two-electron reduced form of TR, and the enzyme may cycle between two-electron reduced and oxidized forms in this reaction. The relatively high rate of quinone reduction by A. thaliana thioredoxin reductase accompanied by their redox cycling, confers pro-oxidant properties to this antioxidant enzyme. These factors make plant TR an attractive target for redox active and alkylating pesticide action.
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PMID:Interaction of quinones with Arabidopsis thaliana thioredoxin reductase. 954 49

Sulforaphane (SF), a glucosinolate-derived isothiocyanate found in cruciferous vegetables, is considered an anticarcinogenic component in broccoli. Sulforaphane induces a battery of detoxification enzymes, including quinone reductase (QR). Induction is thought to be mediated through a common regulatory region termed the antioxidant response element (ARE). To test the hypothesis that the antioxidant selenoprotein thioredoxin reductase (TR) may be induced as part of this coordinated host-defense response to dietary anticarcinogenic compounds, TR activity was measured in livers of rats pair-fed diets containing SF and/or broccoli (n = 6/group). At the doses used, neither SF nor broccoli alone significantly elevated TR activity, whereas treatments containing both broccoli and SF caused a significant increase in TR activity. Glutathione peroxidase (GSH-Px), a second selenium-dependant enzyme with antioxidant activity, was downregulated in rats fed both SF and broccoli, compared to the control diet.A second experiment, using mouse hepatoma Hepa1c1c7 cells, tested whether an interaction exists between selenium (Se) and SF in TR inducibility, since Se is known to induce TR activity. Selenium (2.5 &mgr;M) plus SF (2.0 &mgr;M) caused significantly greater TR activity than either treatment alone. All treatments with added Se or SF caused significantly greater TR activities than no Se or SF treatment. Glutathione peroxidase activity was elevated by Se, but not by SF. These data suggest that TR, known to be regulated by Se, is also upregulated as part of a host response to the dietary anticarcinogen SF, a trait not shared by another Se-dependent enzyme, GSH-Px.
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PMID:Induction of hepatic thioredoxin reductase activity by sulforaphane, both in Hepa1c1c7 cells and in male Fisher 344 rats. 1274 46

From Bacillus subtilis cell extracts, ferredoxin-NADP+ reductase (FNR) was purified to homogeneity and found to be the yumC gene product by N-terminal amino acid sequencing. YumC is a approximately 94-kDa homodimeric protein with one molecule of non-covalently bound FAD per subunit. In a diaphorase assay with 2,6-dichlorophenol-indophenol as electron acceptor, the affinity for NADPH was much higher than that for NADH, with Km values of 0.57 microM vs >200 microM. Kcat values of YumC with NADPH were 22.7 s(-1) and 35.4 s(-1) in diaphorase and in a ferredoxin-dependent NADPH-cytochrome c reduction assay, respectively. The cell extracts contained another diaphorase-active enzyme, the yfkO gene product, but its affinity for ferredoxin was very low. The deduced YumC amino acid sequence has high identity to that of the recently identified Chlorobium tepidum FNR. A genomic database search indicated that there are more than 20 genes encoding proteins that share a high level of amino acid sequence identity with YumC and which have been annotated variously as NADH oxidase, thioredoxin reductase, thioredoxin reductase-like protein, etc. These genes are found notably in gram-positive bacteria, except Clostridia, and less frequently in archaea and proteobacteria. We propose that YumC and C. tepidum FNR constitute a new group of FNR that should be added to the already established plant-type, bacteria-type, and mitochondria-type FNR groups.
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PMID:Purification and characterization of ferredoxin-NADP+ reductase encoded by Bacillus subtilis yumC. 1525 6

Previous studies have demonstrated transcriptional induction of thioredoxin reductase (TR) by sulforaphane (SF) purified from broccoli; the mechanism of induction is via an antioxidant response element (ARE) in the promoter region of the gene. The purpose of the present study was to further characterize the induction of TR by compounds in broccoli and to determine if SF is the primary compound responsible for this induction. Aqueous extracts were made from broccoli with low or high concentrations of selenium (Se) and/or SF and tested in a TR/luciferase reporter gene system in cultured cells. Phenolic acids commonly found in broccoli (sinapic, caffeic, ferulic, and protocatechuic) and ascorbic acid were also tested. At SF concentrations of < or =2 microM, broccoli extracts and purified SF activated transcription equally well, but 4 microM SF in broccoli extracts resulted in almost twice as much induction as 4 microM purified SF (P < 0.05). All broccoli extracts significantly increased TR and quinone reductase activity relative to controls (P < 0.05), but only extracts highest in Se increased glutathione peroxidase activity (P < 0.05). No phenolic acids tested induced transcription, but ascorbic acid resulted in modest dose-dependent induction between 0 and 120 microM (P < 0.001). These data suggest that SF accounts for most of the ARE-activated transcriptional induction of antioxidant genes by broccoli.
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PMID:Phytochemicals in broccoli transcriptionally induce thioredoxin reductase. 1599 10

Ferritins, an ancient family of protein nanocages, concentrate iron in iron-oxy minerals for iron-protein biosynthesis and protection against oxy radical damage. Of the two genetic mechanisms that regulate rates of ferritin-L synthesis, DNA transcription and mRNA translation, more is known about mRNA regulation where iron targets complexes of an mRNA structure, the iron-responsive element (IRE) sequence, and ferritin IRE repressors (iron regulatory proteins 1 and 2). Neither the integration of mRNA and DNA regulation nor the ferritin-L DNA promoter are well studied. We now report the combined effects of DNA transcription and mRNA translation regulation of ferritin-L synthesis. First, the promoter of human ferritin-L, encoding the animal-specific subunit associated with human diseases, was identified, and contained an overlapping Maf recognition element (MARE) and antioxidant responsive element (ARE) that was positively regulated by tert-butylhydroquinone, sulforaphane, and hemin with responses comparable to thioredoxin reductase (ARE regulator) or quinone reductase (MARE/ARE regulator). Iron, a poor regulator of the ferritin-L promoter, was 800 times less effective than sulforaphane. Combining the ferritin-L MARE/ARE and IRE produced a response to hemin that was 3-fold greater than the sum of responses of the MARE/ARE or IRE alone. Regulation of ferritin-L by a MARE/ARE DNA sequence emphasizes the importance of ferritin-L in oxidative stress that complements the mRNA regulation in iron stress. Combining DNA and mRNA mechanisms of regulation, as for ferritin-L, illustrates the advantages of using two types of genetic targets to achieve sensitive responses to multiple signals.
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PMID:DNA and mRNA elements with complementary responses to hemin, antioxidant inducers, and iron control ferritin-L expression. 1621 41

Depending on growth conditions, broccoli may be enriched in the isothiocyanate sulforaphane and/or the mineral selenium (Se); both compounds may play an important role in the reduction of intracellular oxidative stress and chronic disease prevention. Sulforaphane up-regulates transcription of Phase II detoxification proteins (e.g. quinone reductase [QR]), whereas Se is needed for the production of thioredoxin reductase (TR) and glutathione peroxidase-1 (GPx1), both of which exhibit antioxidant activity. The objective of the present study was to determine whether the fertilization of broccoli with Se increases the antioxidant ability of broccoli. Hydrogen peroxide-induced DNA single-strand breaks (measured by single cell electrophoresis, Comet assay) and activity of antioxidant enzymes (GPx, TR and QR) were measured in mouse hepatoma cells (Hepa 1c1c7 cells) treated with purified sulforaphane, sodium selenite or extracts of selenized broccoli. When supplied separately as chemically pure substances, sodium selenite was more effective than sulforaphane for reduction of single-strand breaks. Se-fertilized broccoli extracts were the most effective for reduction of DNA single-strand breaks, and extracts that contained 0.71 microM Se and 0.08 microM sulforaphane inhibited 94% of DNA single-strand breaks. A significant positive association (r = 0.81, p = 0.009) between GPx1 activity and inhibition of DNA single-strand breaks as well as a 24h lag time between addition of Se, sulforaphane or broccoli extract and inhibition of single-strand breaks suggests that some of the antioxidant protection is mediated through selenoproteins. Conversely, fertilization of broccoli with Se decreased the ability of broccoli extract to induce QR activity. These results demonstrate that Se and sulforaphane, alone or as a component of broccoli, may help decrease oxidative stress. They further suggest that Se is the most important for decreasing oxidative stress, but maximizing the Se content of broccoli also may compromise its ability to induce Phase II detoxification proteins.
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PMID:Aqueous extracts of selenium-fertilized broccoli increase selenoprotein activity and inhibit DNA single-strand breaks, but decrease the activity of quinone reductase in Hepa 1c1c7 cells. 1637 50

Selenite and organoselenium compounds have been examined at supranutritional levels for their ability to influence the activity and mRNA levels of chemoprotective enzymes in the livers of selenium-sufficient mice and the changes compared to those elicited by oltipraz. Compounds investigated included novel selenocysteine prodrugs that have previously been evaluated for their ability to reduce the tumorigenicity of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in mice. Following seven daily doses (i.g.), all compounds except 2-methylselenazolidine-4(R)-carboxylic acid (MSCA) increased thioredoxin reductase activity (43-92%) but only for 2-oxoselenazolidine-4(R)-carboxylic acid (OSCA) was there an accompanying increase in mRNA. No compound enhanced glutathione peroxidase activity, although sodium selenite significantly elevated the mRNA of this enzyme. Oltipraz was an efficacious inducer of both thioredoxin reductase and glutathione peroxidase mRNAs. Sodium selenite, selenazolidine-4(R)-carboxylic acid (SCA), and OSCA elevated NAD(P)H-quinone oxidoreductase mRNA but only for OSCA was the elevation in mRNA accompanied by an increase in enzyme activity. L-Selenocystine significantly increased this activity without increasing mRNA levels. Sodium selenite, L-selenocystine, L-selenomethionine, and Se-methyl-L-selenocysteine all enhanced glutathione S-transferase activity. The increased activity with sodium selenite was accompanied by increases in mRNAs of Gst alpha, Gst mu and Gst pi classes, while for L-selenocystine and Se-methyl-L-selenocysteine, only an elevation in the mRNA for the Gst alpha class was observed. Gst alpha and Gst mu class mRNAs were elevated by OSCA without a significant elevation in enzyme activity. SCA and MSCA both elevated a Gst pi mRNA and MSCA elevated Gst mu in addition. By comparison, oltipraz only significantly elevated the mRNA of Gst mu, adding to the conclusion that across the entire study, no selenium compound appears to be acting purely through the antioxidant response typified by oltipraz. Despite their chemical similarity, the three cysteine prodrugs, SCA, MSCA, and OSCA, each produced its own unique pattern of effects on protective enzymes and none was identical to the pattern elicited by sodium selenite, L-selenocystine, L-selenomethionine, and Se-methyl-L-selenocysteine. The study also shows that after 7 days of administration, there was only occasional concordance between elevations in mRNA and enzyme activity for any selenium compound and for any protective enzyme, there was no response in common for all selenium compounds.
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PMID:Effect of selenium-containing compounds on hepatic chemoprotective enzymes in mice. 1645 16

Novel selenazolidines, designed as l-selenocysteine prodrugs and potential cancer chemopreventive agents, were examined for their ability to affect the transcription of murine hepatic chemoprotective enzymes. Compounds investigated were selenazolidine-4(R)-carboxylic acid (SCA) and six 2-substituted derivatives that cover a C log P range of -0.512 to -3.062. Their biological effects were compared with those of L-selenocystine. Gene transcripts were examined 24 h after a single dose, administered i.p. and i.g., and covered a range of chemoprotective enzymes; alpha, mu and pi class glutathione transferases (Gsts), UDP-glucuronosyltransferases (Ugts) 1a1, 1a6, 1a9, and 2b5, glutathione peroxidase 1 (Gpx), thioredoxin reductase (Tr), NAD(P)H-quinone oxidoreductase 1 (Nqo), and microsomal epoxide hydrolase (Meh). When given i.g., 2-butyl SCA (BSCA) resulted in elevations in alpha, mu and pi class Gsts, Ugt1a6, Tr, and Gpx, and 2-phenyl SCA (PhSCA) elevated GstP, Ugt1a9, Tr, Gpx (3 kb), and Meh. Other derivatives with C log P values both lower [2-(2'-hydroxy)phenyl SCA (PhOHSCA) and 2-methyl SCA (MSCA)] and higher [2-cyclohexyl SCA (ChSCA) and 2-oxo SCA (OSCA)] than BSCA and PhSCA elevated far fewer transcripts; PhOHSCA (Ugt1a1, Gpx), MSCA (Ugt1a1, Meh), ChSCA (Ugt1a1, Ugt1a9), and OSCA (Ugt1a6, Ugt1a9, GstM). When given i.p., the most pervasive transcript changes were parallel increases in Nqo and Tr transcripts which occurred with BSCA, PhSCA, MSCA, and OSCA. PhSCA also increased GstP, and PhOHSCA increased Ugt1a1 and Ugt1a6 levels. Unique among the compounds, PhSCA reduced the transcript levels of GstA, and the 1.6 kb transcript of Gpx although only when given i.p. Neither l-selenocystine nor SCA affected the level of any transcript and no compound altered the amount of Ugt2b5 mRNA. Despite chemical similarity and common ability to potentially serve as a source of l-selenocysteine, each selenazolidine compound appeared to elicit a unique pattern of mRNA responses and by either route of administration, there was no correlation between the magnitude of response of any gene and the calculated C log P values of the organoselenium compounds.
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PMID:Acute effects of novel selenazolidines on murine chemoprotective enzymes. 1676 27

Murine (Hepa1c1c7) hepatoma cells are a suitable in vitro system for investigating the regulation of chemoprotective enzymes by selenazolidines, novel l-selenocysteine prodrugs developed as potential chemopreventive agents. They are less sensitive to the cytotoxic effects of both selenite and the less toxic selenazolidines than rat hepatoma (H4IIE) cells. All four selenazolidine 4-carboxylic acid (SCA) derivatives examined elevated thioredoxin reductase (Txnrd1), alpha-class glutathione transferases (Gsta), and UDP-glucuronosyltransferase (Ugt)1a6 mRNAs. NAD(P)H-quinone oxidoreductase (Nqo1) was induced by the three 2-alkyl derivatives (2-cyclohexylSCA, 2-butylSCA, and 2-methylSCA) but not SCA itself. Transcripts of mu- and pi-class glutathione transferases were induced only by 2-cyclohexylSCA and 2-butylSCA. Only Gsta and Txnrd1 transcripts were elevated by l-selenomethionine, l-selenocystine, or Se-methyl-l-selenocysteine. Txnrd1, Gsta, Nqo1, and Gstp responses to selenazolidines were all abolished by actinomycin D while Ugt1a6 responses were not. Induction responses to the selenazolidines were also eliminated (most) or reduced (Txnrd1 by 2-methylSCA) by cycloheximide, with the exception of Ugt1a6. The Ugt1a6 mRNA levels in the presence of SCAs and cycloheximide were similar to those with cycloheximide alone, and were almost double those of vehicle-treated cells. Thus, Hepa1c1c7 cells appear to provide a viable platform for the study of protective enzyme regulation by selenocompounds, and with the exception of Ugt1a6, the mRNA elevations from selenazolidines are transcriptionally dependent.
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PMID:Murine hepatoma (Hepa1c1c7) cells: a responsive in vitro system for chemoprotective enzyme induction by organoselenium compounds. 1711 78


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