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)

Dworkin, Martin (University of Minnesota, Minneapolis), and Donald J. Niederpruem. Electron transport system in vegetative cells and microcysts of Myxococcus xanthus. J. Bacteriol. 87:316-322. 1964.-Respiration by intact cells of the fruiting myxobacterium Myxococcus xanthus is cyanide-sensitive and can be demonstrated in the vegetative cells but not in the microcysts. Cell-free particles from both vegetative cells and microcysts have cyanide-sensitive reduced nicotinamide adenine dinucleotide (NADH) oxidase, diaphorase, NADH cytochrome c reductase, and cytochrome oxidase activities. While the vegetative cell specific activities for NADH oxidase and diaphorase are slightly higher than those for the microcysts, the microcysts have ten times the cytochrome c reductase and cytochrome oxidase activities of the vegetative cells. Furthermore, the respiration of the microcyst particles is considerably less cyanide-sensitive than is that of the vegetative-cell particles. Difference spectra of the cell-free particles of vegetative cells and microcysts are qualitatively identical, showing the presence of b- and c-type cytochrome and flavoprotein. The a-type pigments are clearly present in the extracts of the vegetative cells and are suggested by the spectrum of the microcyst particles. The cytochrome oxidase activity of both extracts is consistent with the presence of a-type pigments in both. The spectra of the carbon monoxide-binding pigments were determined and, by this parameter, qualitative differences appear between the vegetative cells and the microcysts.
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PMID:ELECTRON TRANSPORT SYSTEM IN VEGETATIVE CELLS AND MICROCYSTS OF MYXOCOCCUS XANTHUS. 1415 Oct 50

VanDemark, P. J. (University of South Dakota, Vermillion), and P. F. Smith. Respiratory pathways in the Mycoplasma. II. Pathway of electron transport during oxidation of reduced nicotinamide adenine dinucleotide by Mycoplasma hominis. J. Bacteriol. 88:122-129. 1964.-Unlike the flavin-terminated respiratory pathway of the fermentative Mycoplasma, the respiratory chain of the nonfermentative M. hominis strain 07 appears to be more complex, involving quinones and cytochromes in addition to flavins. In addition to reduction by reduced nicotine adenine dinucleotide (NADH) and reduced nicotine adenine dinucleotide phosphate, nonpyridine nucleotide-linked reduction of the respiratory chain of this organism occurred with succinate, lactate, and short-chained acyl coenzyme A derivatives as electron donors. Enzymes catalyzing the oxidation of NADH included an NADH oxidase, a diaphorase, a quinone reductase, and a cytochrome c reductase. The oxidation of NADH was sensitive to a variety of inhibitors, including 10(-4)m Atabrine, 10(-3)m sodium amytal, 10(-5)mp-chloromercuribenzoate, 10(-4)m antimycin A, and 10(-4)m potassium cyanide. The oxidase was resolved by the addition of 5% trichloroacetic acid and reactivated by the addition of flavin adenine dinucleotide but not flavin mononucleotide. The M. hominis sonic extract contained an NADH-coenzyme Q reductase. The oxidation of NADH was stimulated by the addition of either menadione or vitamin K(2) (C(35)). The oxidase was inactivated by extraction with ether or irradiation at 360 mmu. The ether-inactivated enzyme was partially reactivated by the addition of "lipid" extract of the enzyme and coenzyme Q(6). Difference spectra of the cell extracts revealed the presence of "b" and "a" type cytochromes. These cell extracts were found to contain a cyanide-and azide-sensitive cytochrome oxidase and catalase.
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PMID:RESPIRATORY PATHWAYS IN THE MYCOPLASMA. II. PATHWAY OF ELECTRON TRANSPORT DURING OXIDATION OF REDUCED NICOTINAMIDE ADENINE DINUCLEOTIDE BY MYCOPLASMA HOMINIS. 1419 76

The study objective was to use pulmonary arterial endothelial cells to examine kinetics and mechanisms contributing to the disposition of the quinone 2,3,5,6-tetramethyl-1,4-benzoquinone (duroquinone, DQ) observed during passage through the pulmonary circulation. The approach was to add DQ, durohydroquinone (DQH2), or DQ with the cell membrane-impermeant oxidizing agent, ferricyanide (Fe(CN)6(3)-), to the cell medium, and to measure the medium concentrations of substrates and products over time. Studies were carried out under control conditions and with dicumarol, to inhibit NAD(P)H:quinone oxidoreductase 1 (NQO1), or cyanide, to inhibit mitochondrial electron transport. In control cells, DQH2 appears in the extracellular medium of cells incubated with DQ, and DQ appears when the cells are incubated with DQH2. Dicumarol blocked the appearance of DQH2 when DQ was added to the cell medium, and cyanide blocked the appearance of DQ when DQH2 was added to the cell medium, suggesting that the two electron reductase NQO1 dominates DQ reduction and mitochondrial electron transport complex III is the predominant route of DQH2 oxidation. In the presence of cyanide, the addition of DQ also resulted in an increased rate of appearance of DQH2 and stimulation of cyanide-insensitive oxygen consumption. As DQH2 does not autoxidize-comproportionate over the study time course, these observations suggest a cyanide-stimulated one-electron DQ reduction and durosemiquinone (DQ*-) autoxidation. The latter processes are apparently confined to the cell interior, as the cell membrane impermeant oxidant, ferricyanide, did not inhibit the DQ-stimulated cyanide-insensitive oxygen consumption. Thus, regardless of whether DQ is reduced via a one- or two-electron reduction pathway, the net effect in the extracellular medium is the appearance of DQH2. These endothelial redox functions and their apposition to the vessel lumen are consistent with the pulmonary endothelium being an important site of DQ reduction to DQH2 observed in the lungs.
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PMID:Impact of pulmonary arterial endothelial cells on duroquinone redox status. 1518 97

Severely Ca-deficient Triticum aestivum L. seedlings accumulated high levels of nitrite and moderate levels of nitrate and organic nitrogen, but contained unaltered levels of hydroxylamine. Nitrite accumulation was not related to molybdenum deficiency, or altered cellular pH. Nitrate reductase was decreased by Ca deficiency, apparently by repression of enzyme synthesis from accumulated nitrite and not by inhibition of enzyme activity. Nitrite reductase and NADP diaphorase activities were not affected by Ca deficiency, and Ca did not restore activity to nitrite reductase inactivated by cyanide. The results indicated that the role of Ca is in intracellular transport of nitrite and not in induction or activity of enzymes.
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PMID:Evidence for a role of calcium in nitrate assimilation in wheat seedlings. 1665 39

THE ASSIMILATORY NITRATE REDUCTASE (NADH: nitrate oxidoreductase, E.C. 1.6.6.2.) from the marine diatom Thalassiosira pseudonana, Hasle and Heimdal, has been purified 200-fold and characterized. The regulation of nitrate reductase in response to various conditions of nitrogen nutrition has been investigated.Nitrate reductase activity is repressed by the presence of ammonium in vivo, and its synthesis is derepressed when ammonium is absent. The derepression process is sensitive to cycloheximide and apparently requires protein synthesis. Repression of enzyme activity by ammonium is neither inhibited nor delayed by the presence of cycloheximide. In vitro, ammonium does not inhibit enzyme activity.NADH is the physiological electron donor for the enzyme in a flavin-dependent reaction. Spectral studies have indicated the presence of a b-type cytochrome associated with the enzyme. It is possible to observe enzymatic oxidation-reduction reactions which represent partial functions of the over-all electron transport capacity of this enzyme. Nitrate reductase will accept electrons from artificial electron donors such as reduced methyl viologen in a flavin-independent reaction. Further, dithionitereduced flavin adenine dinucleotide can donate electrons to the enzyme to reduce nitrate to nitrite. Finally, the nitrate reductase will exhibit a diaphorase activity and reduce the artificial electron acceptor mammalian cytochrome c in flavin-adeninedinucleotide-dependent reaction.Inhibition studies with potassium cyanide, sodium azide, and o-phenanthroline have yielded indirect evidence for metal component (s) of the enzyme.The inhibition of the NADH-requiring enzyme activities by p-hydroxymercuribenzoate has shown that an essential sulfhydryl group is involved in the initial portion of the electron transport. Heat treatment exerts an effect similar to the p-hydroxymercuribenzoate inhibition; namely, the NADH-requiring activities are rapidly inactivated, whereas the terminal nitrate-reducing activities are relatively stable to heat.The T. pseudonana nitrate reductase molecule has the hydrodynamic properties of an ellipsoid with a frictional coefficient of 1.69 and a molecular weight of 330,000.
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PMID:Purification and Characterization of the Nitrate Reductase from the Diatom Thalassiosira pseudonana. 1665 41

The ethanol-producing bacterium Zymomonas mobilis can serve as a model organism for the study of rapid catabolism and inefficient energy conversion in bacteria. Some basic aspects of its physiology still remain poorly understood. Here, the energy-spilling pathways during uncoupled growth, the structure and function of electron transport chain, and the possible reasons for the inefficient oxidative phosphorylation are analysed. Also, the interaction between ethanol synthesis and respiration is considered. The search for mechanisms of futile transmembrane proton cycling, as well as identification of respiratory electron transport complexes, like the energy-coupling NAD(P)H:quinone oxidoreductase and the cyanide-sensitive terminal oxidase(s), are outlined as the key problems for further research of Z. mobilis energy metabolism.
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PMID:Physiology of Zymomonas mobilis: some unanswered questions. 1701 Jun 96

Conditions for the reversible dissociation of flavin mononucleotide (FMN) from the membrane-bound mitochondrial NADH:ubiquinone oxidoreductase (complex I) are described. The catalytic activities of the enzyme, i.e. rotenone-insensitive NADH:hexaammineruthenium III reductase and rotenone-sensitive NADH:quinone reductase decline when bovine heart submitochondrial particles are incubated with NADH in the presence of rotenone or cyanide at alkaline pH. FMN protects and fully restores the NADH-induced inactivation whereas riboflavin and flavin adenine dinucleotide do not. The data show that the reduction of complex I significantly weakens the binding of FMN to protein thus resulting in its dissociation when the concentration of holoenzyme is comparable with K(d ( approximately 10(-8)M at pH 10.0).
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PMID:Reversible dissociation of flavin mononucleotide from the mammalian membrane-bound NADH: ubiquinone oxidoreductase (complex I). 1803 77

It has already been reported that in vivo muscle necrosis induced by various phenylenediamine derivatives correlated with their in vitro autoxidation rate [9]. Now in a more detailed investigation of the cytotoxic mechanism of a ring-methylated phenylenediamine known as tetramethylphenylenediamine or durenediamine (DD) towards isolated rat hepatocytes has been carried out. Cytotoxicity was preceded by ROS formation which was markedly increased by inactivating DT-diaphorase or catalase but were prevented by a subtoxic concentration of the mitochondrial respiratory inhibitor cyanide. This suggests that ROS generation could be attributed to a futile two-electron redox cycle involving oxidation of phenylenediamine to the corresponding diimine by the mitochondrial electron transfer chain and re-reduction by the DT-diaphorase. Endocytosis inhibitors, lysosomotropic agents or lysosomal protease inhibitors also prevented DD-induced cytotoxicity suggesting that DD-induced ROS caused lysosomal damage and protease activation in hepatocytes. Furthermore preincubation with deferoxamine (a ferric iron chelator) or addition of antioxidants, catalase or ROS scavengers (mannitol, tempol or dimethylsulfoxide) prevented DD cytotoxicity. These results suggest that H(2)O(2) reacts with lysosomal Fe(2+) to form "ROS" which causes lysosomal lipid peroxidation, membrane disruption, protease release and cell death.
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PMID:Tetramethylphenylenediamine-induced hepatocyte cytotoxicity caused by lysosomal labilisation and redox cycling with oxygen activation. 1822 36

The respiratory chain of the ethanol-producing bacterium Zymomonas mobilis is able to oxidize both species of nicotinamide cofactors, NADH and NADPH. A mutant strain with a chloramphenicol-resistance determinant inserted in ndh (encoding an NADH : CoQ oxidoreductase of type II) lacked the membrane NADH and NADPH oxidase activities, while its respiratory D-lactate oxidase activity was increased. Cells of the mutant strain showed a very low respiration rate with glucose and no respiration with ethanol. The aerobic growth rate of the mutant was elevated; exponential growth persisted longer, resulting in higher biomass densities. For the parent strain a similar effect of aerobic growth stimulation was achieved previously in the presence of submillimolar cyanide concentrations. It is concluded (i) that the respiratory chain of Z. mobilis contains only one functional NAD(P)H dehydrogenase, product of the ndh gene, and (ii) that inhibition of respiration, whether resulting from a mutation or from inhibitor action, stimulates Z. mobilis aerobic growth due to redirection of the NADH flux from respiration to ethanol synthesis, thus minimizing accumulation of toxic intermediates by contributing to the reduction of acetaldehyde to ethanol.
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PMID:NADH dehydrogenase deficiency results in low respiration rate and improved aerobic growth of Zymomonas mobilis. 1831 45

2,3-Dimethoxy 1,4-naphthoquinone (DMNQ), which redox cycles via two-electron reduction, mediates reduction of the cell-impermeative tetrazolium dye WST-1 in kidney epithelial cells (MDCK), which express high levels of NQO1, but not in HL60 or CHO cells, which are NQO1 deficient. DMNQ-dependent WST-1 reduction by MDCK cells was strongly inhibited by low concentrations of the NQO1 inhibitor dicoumarol and was also inhibited by diphenyleneiodonium, capsaicin, and superoxide dismutase (SOD), but not by the uncoupler FCCP or the complex IV inhibitor cyanide. This suggests that DMNQ-dependent WST-1 reduction by MDCK cells is catalyzed by NQO1 via redox cycling and plasma membrane electron transport (PMET). Interestingly, we observed an association between DMNQ/WST-1 reduction and extracellular H(2)O(2) production as determined by Amplex red. Exposure of MDCK cells to DMNQ for 48 h caused cellular toxicity that was extensively reversed by co-incubation with dicoumarol or exogenous SOD, catalase, or N-acetylcysteine. No effects were observed in NQO1-deficient CHO and HL60 cells. In conclusion, we have developed a simple real-time cellular assay for NQO1 and show that PMET plays a significant role in DMNQ redox cycling via NQO1, leading to cellular toxicity in cells with high NQO1 levels.
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PMID:Evidence for NAD(P)H:quinone oxidoreductase 1 (NQO1)-mediated quinone-dependent redox cycling via plasma membrane electron transport: A sensitive cellular assay for NQO1. 1993 48


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