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:1.6.99.5 (NADH dehydrogenase)
2,135 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

EPR spectroscopy was used to investigate the cytochrome P-450-dependent steroid hydroxylase ecdysone 20-mono-oxygenase of the cotton leafworm (Spodoptera littoralis) and the redox centres associated with membranes from the fat-body mitochondrial fraction. Intense features at g = 2.42, 2.25 and 1.92 from oxidized mitochondrial membranes have been assigned to the low-spin haem form of ferricytochrome P-450, probably of ecdysone 20-mono-oxygenase. High-spin cytochrome P-450 (substrate-bound) was tentatively assigned to a signal at g = 8.0, which was detectable from membranes as prepared. An EPR signal characteristic of a [2Fe-2S] cluster detected from the soluble mitochondrial matrix fraction has been shown to be distinct from the signals associated with mitochondrial NADH dehydrogenase and succinate dehydrogenase, and has therefore been attributed to a ferredoxin. We conclude that the S. littoralis fat-body mitochondrial electron-transport system involved in steroid 20-hydroxylation comprises both ferredoxin and cytochrome P-450 components, and thus resembles the enzyme systems of adrenocortical mitochondria. EPR signals characteristic of the respiratory chain were also observed from fat-body mitochondria and assigned to the iron-sulphur clusters associated with Complex I (Centres N1, N2), Complex II (Centres S1, S3), Complex III (the Rieske centre), and the copper centre of Complex IV, demonstrating similarities to mammalian mitochondria. The reduced membrane fraction also yielded a major resonance at g = 2.09 and 1.88 characteristic of the [4Fe-4S] cluster of electron-transferring flavoprotein: ubiquinone oxidoreductase. As the fat-body is the major metabolic organ of insects, this protein is presumably required for the beta-oxidation of fatty acids in mitochondria. High-spin haem signals in the low-field region of spectra also demonstrated that the mitochondrial fraction contains relatively high concentrations of catalase.
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PMID:EPR spectroscopic characterization of the iron-sulphur proteins and cytochrome P-450 in mitochondria from the insect Spodoptera littoralis (cotton leafworm). 774 2

Isolated mitochondria supplemented with succinate or NAD(+)-linked substrates generate hydrogen peroxide (H2O2) in State 4 and the generation is enhanced by antimycin A, an inhibitor of the respiratory chain. Superoxide is a stoichiometric precursor of mitochondrial H2O2 because the ratio of O2-/H2O2 generation rates is close to 2.0 and is generated by an autoxidizable component in the NADH dehydrogenase and the ubiquinone-cytochrome b site. Lipid peroxidation is a free radical-mediated degradation of polyunsaturated fatty acids. Lipid-peroxidation reactions by bovine submitochondrial particles are supported by NADH or NADPH in the presence of ADP-Fe3+ chelate. Electrons from NADH are supplied to the reactions from a component between the substrate site and the rotenone-sensitive site of the NADH dehydrogenase. The peroxidation is dependent on the rate of electron input into the respiratory chain and on the concentration of reduced ubiquinone. Alteration of inner-membrane components and damage to electron-transfer activities of submitochondrial particles are induced by lipid peroxidation. 1-Melhyl-4-phenylpyridinium (MPP+), a metabolite of a parkinsonism-inducing drug, induces NADH-dependent superoxide formation and enhances NADH-dependent lipid peroxidation in submitochondrial particles, indicating that the oxidative stress induced by MPP+ may potentiate its toxicity in dopamine neurons.
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PMID:[Superoxide formation and lipid peroxidation by the mitochondrial electron-transfer chain]. 777 32

Exposure of cells to hydrogen peroxide (H2O2) mediates adaptive responses or oxidative damage, depending on the magnitude of the challenge. Determining the threshold for peroxide-mediated oxidative stress thus requires quantitation of the changes in endogenous H2O2 production. The intracellular steady-state concentrations of H2O2 were measured in intact Escherichia coli under different conditions. Compounds that block electron transport at NADH dehydrogenase (rotenone) or between ubiquinone and cytochrome b (antimycin) showed that univalent reduction of O2 can occur at these sites in vivo to form superoxide anion (O2-), in agreement with reports for mammalian mitochondria. Mutational inactivation of different components of the respiratory chain showed that H2O2 production also depended on the energy status of the cell and on the arrangement of respiratory chain components corresponding to particular growth conditions. Production rates for O2- and H2O2 were linearly related to the number of active respiratory chains that reached maximal values during exponential growth. In the strains defective in respiratory chain components, catalase activity was regulated to compensate for changes in the H2O2 production rates, which maintained intracellular H2O2 at 0.1-0.2 microM during aerobic growth over a wide range of cell densities. The expression of a katG'::lacZ fusion (reporting transcriptional control of the catalase-hydroperoxidase I gene) was increased by H2O2 given either as a pulse or as a steady production. This response not only depended on the type and severity of the stimulus but was also strongly influenced by the growth phase of the cells.
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PMID:Metabolic sources of hydrogen peroxide in aerobically growing Escherichia coli. 777 20

The dependence of electron flux through quinone-reducing and quinol-oxidizing pathways on the redox state of the ubiquinone (Q) pool was investigated in plant mitochondria isolated from potato (Solanum tuberosum cv. Bintje, fresh tissue and callus), sweet potato (Ipomoea batatas) and Arum italicum. We have determined the redox state of the Q pool with two different methods, the Q-electrode and Q-extraction techniques. Although results from the two techniques agree well, in all tissues tested (with the exception of fresh potato) an inactive pool of QH2 was detected by the extraction technique that was not observed with the electrode. In potato callus mitochondria, an inactive Q pool was also found. An advantage of the extraction method is that it permits determination of the Q redox state in the presence of substances that interfere with the Q-electrode, such as benzohydroxamate and NADH. We have studied the relation between rate and Q redox state for both quinol-oxidizing and quinone-reducing pathways under a variety of metabolic conditions including state 3, state 4, in the presence of myxothiazol, and benzohydroxamate. Under state 4 conditions or in the presence of myxothiazol, a non-linear dependence of the rate of respiration on the Q-redox state was observed in potato callus mitochondria and in sweet potato mitochondria. The addition of benzohydroxamate, under state 4 conditions, removed this non-linearity confirming that it is due to activity of the cyanide-resistant pathway. The relation between rate and Q redox state for the external NADH dehydrogenase in potato callus mitochondria was found to differ from that of succinate dehydrogenase. It is suggested that the oxidation of cytoplasmic NADH in vivo uses the cyanide-resistant pathway more than the pathway involving the oxidation of succinate. A model is used to predict the kinetic behaviour of the respiratory network. It is shown that titrations with inhibitors of the alternative oxidase cannot be used to demonstrate a pure overflow function of the alternative oxidase.
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PMID:The relationship between electron flux and the redox poise of the quinone pool in plant mitochondria. Interplay between quinol-oxidizing and quinone-reducing pathways. 781 62

Until now ubisemiquinones associated with NADH:ubiquinone oxidoreductase (complex I) have been reported to occur in isolated enzyme and in tightly coupled submitochondrial particles. In this report it is shown that ubisemiquinones are always detectable during steady-state electron transfer from NADH to ubiquinone, independent of the type of inner-membrane preparation used. The EPR signal of the rotenone-sensitive ubisemiquinones could be detected not only in coupled MgATP submitochondrial particles, but also in routine preparations of uncoupled submitochondrial particles and in mitochondria. The ubisemiquinone formation in coupled preparations was completely insensitive to uncouplers. The maximal radical concentration during steady-state electron transfer from NADH to quinone was equal to that of iron-sulphur cluster 2. Experiments with antimycin, myxothiazol and 2-thenoyltrifluoroacetone demonstrated that about half of this radical was associated with complex I, giving a ubisemiquinone concentration of about 0.5 mol semiquinone/mol cluster 2. Uncoupled submitochondrial particles, prepared by extensive sonification, never showed radical signals within 100 ms after mixing with NADH. This was due to the reversible inactivation of the enzyme, caused by elevated temperatures during sonification. In preparations with deliberately heat-inactivated complex I, no radical signals were detected within 200 ms after mixing with NADH; at 1 s, however, radical formation was maximal. Yet, depending on the procedure of reactivation of the complex, in preparations previously treated to inactivate them ubisemiquinone concentrations were always less than in untreated particles. When complex I was in the active state the ubisemiquinone signal was maximal within 40 ms. The results described in this report lead to the conclusion that ubisemiquinones form obligatory intermediates in the reaction of NADH dehydrogenase with ubiquinone.
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PMID:Ubisemiquinones as obligatory intermediates in the electron transfer from NADH to ubiquinone. 802 8

NADH:ubiquinone reductase (EC 1.6.19.3), or complex I, was isolated from broad bean (Vicia faba L.) mitochondria. Osmotic shock and sequential treatment with 0.2% (v/v) Triton X-100 and 0.5% (w/v) [3-cholamidopropyl)dimethylammonio]-1-propanesulfate (CHAPS) removed all other NADH dehydrogenase activities. Complex I was solubilized in the presence of 4% Triton X-100 and then purified by sucrose-gradient centrifugation in the presence of the same detergent. The second purification step was hydroxylapatite chromatography. Substitution of CHAPS for Triton X-100 helped remove contaminants such as ATPase. The high molecular mass complex is composed of at least 26 subunits with molecular masses ranging from 6000 to 75,000 kD. The purified complex I reduced ferricyanide and ubiquinone analogs but not cytochrome c. NADPH could not substitute for NADH as an electron donor. The KM for NADH was 20 microM at the optimum pH of 8.0. The NH2-terminal sequence of several subunits was determined, revealing the ambiguous nature of the 42-kD subunit.
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PMID:Purification and preliminary characterization of mitochondrial complex I (NADH: ubiquinone reductase) from broad bean (Vicia faba L.). 810 9

The product of the spontaneous dimerization and decarboxylation of aminoethylcysteine ketimine (simply named the dimer in this note) has been investigated for a possible biochemical activity. It has been found that the dimer inhibits the ADP-dependent oxidation of NAD(+)-linked substrates in rat liver mitochondria and electron transport from NADH to O2 in bovine heart submitochondrial particles (SMP). Oxidation of succinate by SMP is not impaired by concentrations of the dimer inhibiting almost totally NADH oxidation. Furthermore, the dimer did not affect the rotenone-insensitive electron transfer from NADH to menadione. These results give a preliminary indication suggesting that the dimer inhibits electron flow from NADH dehydrogenase to ubiquinone at or near the rotenone binding site(s). The dimer inhibition falls in the same range exhibited by some neurotoxins which are known to interact with the rotenone binding site.
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PMID:Aminoethylcysteine ketimine decarboxylated dimer inhibits mitochondrial respiration by impairing electron transport at complex I level. 813 20

In mammalian cells the membrane-bound NADH-quinone oxidoreductase serves as the entry point for oxidation of NADH in the respiratory chain and as the proton-translocating unit which conserves the free energy of the enzyme intramolecular redox reactions as the free energy of the electrochemical proton gradient across the coupling membrane. This review summarizes the kinetic properties of the mammalian enzyme. Emphasis is placed on the hysteretic properties of the enzyme as related to the possible control of intramitochondrial NADH oxidation and to the mechanism of the enzyme interaction with ubiquinone. Recent evidence for participation of flavin and the protein-bound ubisemiquinone pair in the enzyme-catalyzed proton translocation mechanism are discussed.
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PMID:Kinetics, control, and mechanism of ubiquinone reduction by the mammalian respiratory chain-linked NADH-ubiquinone reductase. 822 18

NADH dehydrogenase is the first component of the respiratory chain. It transfers electrons from NADH to ubiquinone and concomitantly establishes a proton motive force across the membrane. Salmonella typhimurium mutants defective in this enzyme were isolated in a screen for strains with increased expression of beta-galactosidase from a hemA-lacZ protein fusion. This unexpected phenotype results from stabilization of the hybrid protein during carbon starvation and is apparently due to an energy requirement for proteolytic attack. Sequence analysis of DNA fragments cloned from an insertion mutant indicates that S. typhimurium has a large cluster of genes encoding the energy-conserving NADH dehydrogenase, similar to one recently described in Paracoccus denitrificans. These findings establish the potential for genetic analysis of a complex enzyme whose function, especially in proton efflux, is poorly understood.
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PMID:Mutants defective in the energy-conserving NADH dehydrogenase of Salmonella typhimurium identified by a decrease in energy-dependent proteolysis after carbon starvation. 823 29

Mitochondrial NADH:ubiquinone oxidoreductase (complex I) is uncompetitively inhibited by 1,10-phenanthroline (OP). EPR spectroscopy of submitochondrial particles indicates that OP, similarly to rotenone, inhibits electron transfer between the Fe-S clusters of complex I and the ubiquinone pool. The proton-translocating NADH dehydrogenase (NDH1) of E. coli is more sensitive to OP than is NDH1 of Paracoccus. EPR spectroscopy of membranous E. coli NDH1 shows that two slow- and one fast-relaxing Fe-S clusters become detectable upon reduction by NADH in the presence of OP. However, none of them resembles the mitochondrial cluster 2.
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PMID:Studies on the proton-translocating NADH:ubiquinone oxidoreductases of mitochondria and Escherichia coli using the inhibitor 1,10-phenanthroline. 831 63


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