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)

1. NADH-ubiquinone-1 and NADH-menadione reductase activities of Complex I were inhibited by diphenyleneiodonium (apparent Ki 23 and 30 nmol/mg of protein respectively). Reduction of K3Fe(CN)6 and juglone was relatively unaffected. 2. Iodoniumdiphenyl and derivatives were much less effective inhibitors. Compounds with similar ring structures to diphenyleneiodonium, in particular dibenzofuran, were inhibitors of NADH-ubiquinone-1 oxidoreductase. 3. Diphenylene[125I]iodonium specifically labelled a polypeptide of mol.wt. 23500. Maximum incorporation was 1 mol/mol of Complex-I flavin or 1 mol/mol of the 23500-mol.wt. polypeptide. 4. The label associated with this polypeptide was of limited stability, especially at lower pH. 5. Complete inhibition of ubiquinone reduction was achieved when 1 mol of inhibitor was incorporated/mol of Complex-I flavin, but the relationship between inhibition and labelling was not linear. 6. No evidence for covalent interaction between diphenyleneiodonium and the phospholipids of Complex I was obtained. 7. Rotenone increased the apparent affinity of diphenyleneiodonium for the 23500-mol.wt. polypeptide without affecting the maximum incorporation. 8. The 23500-mol.wt. polypeptide was not solubilized by chaotropic agents. Prior treatment of Complex I with chaotropic agents or sodium dodecyl sulphate prevented incorporation of diphenyleneiodonium into this polypeptide.
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PMID:Specific labelling of a constituent polypeptide of bovine heart mitochondrial reduced nicotinamide-adenine dinucleotide-ubiquinone reductase by the inhibitor diphenyleneiodonium. 1 40

The soluble hydrogenase (hydrogen: NAD+ oxidoreductase, EC 1.12.1.2) from Alcaligenes eutrophus H 16 was purified 68-fold with a yield of 20% and a final specific activity (NAD reduction) of about 54 mumol H2 oxidized/min per mg protein. The enzyme was shown to be homogenous by polyacrylamide gel electrophoresis. Its molecular weight and isoelectric point were determined to be 205 000 and 4.85 respectively. The oxidized hydrogenase, as purified under aerobic conditions, was of high stability but not reactive. Reductive activation of the enzyme by H2, in the presence of catalytic amounts of NADH, or by reducing agents caused the hydrogenase to become unstable. The purified enzyme, in its active state, was able to reduce NAD, FMN, FAD, menaquinone, ubiquinone, cytochrome c, methylene blue, methyl viologen, benzyl viologen, phenazine methosulfate, janus green, 2,6-dichlorophenoloindophenol, ferricyanide and even oxygen. In addition to hydrogenase activitiy, the enzyme exhibited also diaphorase and NAD(P)H oxidase activity. The reversibility of hydrogenase function (i.e. H2 evolution from NADH, methyl viologen and benzyl viologen) was demonstrated. With respect to H2 as substrate, hydrogenase showed negative cooperativity; the Hill coefficient was n = 0.4. The apparent Km value for H2 was found to be 0.037 mM. The absorption spectrum of hydrogenase was typical for non-heme iron proteins, showing maxima (shoulders) at 380 and 420 nm. A flavin component could be extracted from native hydrogenase characterized by its absorption bands at 375 and 447 nm and a strong fluorescense at 526 nm.
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PMID:Purification and properties of soluble hydrogenase from Alcaligenes eutrophus H 16. 18 26

NADH:ubiquinone oxidoreductase (complex I) was purified from bovine heart mitochondria by solubilization with n-dodecyl beta-D-maltoside (lauryl maltoside), ammonium sulfate fractionation, and chromatography on Mono Q in the presence of the detergent. Its subunit composition was very similar to complex I purified by conventional means. Complex I was dissociated in the presence of N,N-dimethyldodecylamine N-oxide and beta-mercaptoethanol, and two subcomplexes, I alpha and I beta, were isolated by chromatography. Subcomplex I alpha catalyzes electron transfer from NADH to ubiquinone-1. It is composed of about 22 different and mostly hydrophilic subunits and contains 2.0 nmol of FMN/mg of protein. Among its subunits is the 51-kDa subunit, which binds FMN and NADH and probably contains a [4Fe-4S] cluster also. Three other potential Fe-S proteins, the 75- and 24-kDa subunits and a 23-kDa subunit (N-terminal sequence TYKY), are also present. All of the Fe-S clusters detectable by EPR in complex I, including cluster 2, are found in subcomplex I alpha. The line shapes of the EPR spectra of the Fe-S clusters are slightly broadened relative to spectra measured on complex I purified by conventional means, and the quinone reductase activity is insensitive to rotenone. Similar changes were found in samples of the intact chromatographically purified complex I, or in complex I prepared by the conventional method and then subjected to chromatography in the presence of lauryl maltoside. Subcomplex I beta contains about 15 different subunits. The sequences of many of them contain hydrophobic segments that could be membrane spanning, including at least two mitochondrial gene products, ND4 and ND5. The role of subcomplex I beta in the intact complex remains to be elucidated.
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PMID:Resolution of NADH:ubiquinone oxidoreductase from bovine heart mitochondria into two subcomplexes, one of which contains the redox centers of the enzyme. 133 58

zeta-Crystallin is a major protein in the lens of certain mammals. In guinea pigs it comprises 10% of the total lens protein, and it has been shown that a mutation in the zeta-crystallin gene is associated with autosomal dominant congenital cataract. As with several other lens crystallins of limited phylogenetic distribution, zeta-crystallin has been characterized as an "enzyme/crystallin" based on its ability to reduce catalytically the electron acceptor 2,6-dichlorophenolindophenol. We report here that certain naturally occurring quinones are good substrates for the enzymatic activity of zeta-crystallin. Among the various quinones tested, the orthoquinones 1,2-naphthoquinone and 9,10-phenanthrenequinone were the best substrates whereas menadione, ubiquinone, 9,10-anthraquinone, vitamins K1 and K2 were inactive as substrates. This quinone reductase activity was NADPH specific and exhibited typical Michaelis-Menten kinetics. Activity was sensitive to heat and sulfhydryl reagents but was very stable on freezing. Dicumarol (Ki = 1.3 x 10(-5) M) and nitrofurantoin (Ki = 1.4 x 10(-5) M) inhibited the activity competitively with respect to the electron acceptor, quinone. NADPH protected the enzyme against inactivation caused by heat, N-ethylmaleimide, or H2O2. Electron paramagnetic resonance spectroscopy of the reaction products showed formation of a semiquinone radical. The enzyme activity was associated with O2 consumption, generation of O2- and H2O2, and reduction of ferricytochrome c. These properties indicate that the enzyme acts through a one-electron transfer process. The substrate specificity, reaction characteristics, and physicochemical properties of zeta-crystallin demonstrate that it is an active NADPH:quinone oxidoreductase distinct from quinone reductases described previously.
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PMID:Identification and characterization of the enzymatic activity of zeta-crystallin from guinea pig lens. A novel NADPH:quinone oxidoreductase. 137 Apr 56

1. In both guinea-pig and rat heart, mitochondrial NADH-ubiquinone-reductase and soluble DT-diaphorase accounted for 49-50% and 48-50% of menadione metabolism, respectively. Microsomal NADPH-cytochrome P450-reductase was responsible for less than 1% of menadione reduction. 2. Menadione was a high-affinity substrate for all reductases (Km values from 1 to 10 microM). 3. Marked amounts of O2-. (superoxide anion) were generated as a consequence of cardiac metabolism of menadione. 4. Menadione-induced O2-. generation was about 3-fold higher in guinea-pig than in rat heart. 5. All results were compared with data obtained on guinea-pig and rat liver.
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PMID:One- and two-electron reduction of menadione in guinea-pig and rat cardiac tissue. 139 83

Two new methods have been devised for measuring fumarate reduction by beef heart succinate-ubiquinone oxidoreductase with quinols as electron donors. In one assay the quinone is maintained in the reduced state by coupling fumarate reduction with the DT-diaphorase reaction, in the other assay by the presence of excess dithionite. The advantages of these methods are discussed, along with preliminary characterization of the quinol-protein interaction.
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PMID:Interaction of ubiquinone and vitamin K3 with mitochondrial succinate-ubiquinone oxidoreductase. 151 Jun 89

The respiratory chain of a marine Vibrio alginolyticus contains two types of NADH-quinone reductase (NQR): one is an Na(+)-dependent NQR functioning as an Na+ pump (NQR-1) and the other is an Na(+)-independent NQR (NQR-2). NQR-2 was purified about 55-fold from the membrane of mutant Nap-1 which is devoid of NQR-1, and its properties were compared with those of NQR-1. In contrast to NQR-1, the purified NQR-2 does not require any salts for activity and is not inhibited by up to 0.4 M salts. The optimum pH of NQR-2 is between 6.8 and 7.8, which is about 0.7 ph units lower than that of NQR-1. NQR-2 is insensitive to strong inhibitors of NQR-1 such as p-chloromercuribenzoate, Ag+ and 2-heptyl-4-hydroxyquinoline N-oxide. Using inverted membrane vesicles, it was confirmed that NQR-2 has no capacity to generate a membrane potential. NQR-2 reduces menadione and ubiquinone-1 by a two-electron reduction pathway. Since the NADH-reacting FAD-containing beta-subunit of NQR-1 reduces quinones by a one-electron reduction pathway, the mode of quinone reduction is closely related to energy coupling; the formation of semiquinone radicals as an intermediate is likely to be essential to functioning as an ion pump.
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PMID:Properties of respiratory chain-linked Na(+)-independent NADH-quinone reductase in a marine Vibrio alginolyticus. 154 99

Coenzyme Q (CoQ0) and other quinones were shown to be potent insulin secretagogues in the isolated pancreatic islet. The order of potency was CoQ0 congruent to benzoquinone congruent to hydroquinone-menadione. CoQ6 and CoQ10 (ubiquinone), duroquinone and durohydroquinone did not stimulate insulin release. CoQ0's insulinotropism was enhanced in calcium-free medium and CoQ0 appeared to stimulate only the second phase of insulin release. CoQ0 inhibited inositol mono-, bis- and trisphosphate formation. Inhibitors of mitochondrial respiration (rotenone, antimycin A, FCCP and cyanide) and the calcium channel blocker verapamil, did not inhibit CoQ0-induced insulin release. Dicumarol, an inhibitor of quinone reductase, did not inhibit CoQ0-induced insulin release, but it did inhibit glucose-induced insulin release suggesting that the enzyme and quinones play a role in glucose-induced insulin release. Quinones may stimulate insulin release by mimicking physiologically-occurring quinones, such as CoQ10, by acting on the plasma membrane or in the cytosol. Exogenous quinones may bypass the quinone reductase reaction, as well as many reactions important for exocytosis.
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PMID:Stimulation of insulin release from pancreatic islets by quinones. 172 Mar 33

The respiratory chain-linked NADH-quinone reductase (NQR) and NADH-ferricyanide dehydrogenase (NFD) were extracted from membranes of Escherichia coli by n-dodecyl octaethyleneglycol monoether detergent and purified by DEAE-Sephacel, DEAE-5PW and Bio-Gel HTP column chromatography. The purified NQR contained FAD as a cofactor, catalyzed the reduction of ubiquinone-1 (Q1) and reacted with NADH, but not with deamino-NADH (d-NADH), with an apparent Km of 48 microM. On the other hand, the purified NFD contained FMN as a cofactor, reacted with both NADH and d-NADH, and catalyzed the reduction of ferricyanide but not Q1. NFD showed a high affinity for both NADH and d-NADH with a Km of 7-9 microM. NFD was inactivated, whereas NQR was rather activated, by preincubation with an electron donor in the absence of electron acceptor. These properties were compared with those of activities observed with inverted membrane vesicles with special reference to the generation of inside-positive membrane potential (delta psi). It was found that d-NADH-reactive FMN-containing NFD is a dehydrogenase part of energy-generating NADH-quinone reductase complex. The FAD-containing NQR was very similar to that purified by Jaworowski et al. (Biochemistry (1981) 20, 2041-2047), and reduced Q1 without generating delta psi.
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PMID:Purification of NADH-ferricyanide dehydrogenase and NADH-quinone reductase from Escherichia coli membranes and their roles in the respiratory chain. 267 83

The respiratory chain of a marine bacterium, Vibrio alginolyticus, required Na+ for maximum activity, and the site of Na+ -dependent activation was localized on the NADH-quinone reductase segment. The Na+ -dependent NADH-quinone reductase extruded Na+ as a direct result of redox reaction. It was composed of three subunits, alpha, beta, and gamma, with apparent Mr of 52, 46, and 32 KDa, respectively. The reduction of ubiquinone-1 to ubiquinol proceeded via ubisemiquinone radicals. The former reaction was catalyzed by the FAD-containing beta subunit. This reaction showed no specific requirement for Na+. For the formation of ubiquinol, the presence of the gamma subunit and the FMN-containing alpha subunit was essential. The latter reaction specifically required Na+ for activity and was strongly inhibited by 2-n-heptyl-4-hydroxyquinoline N-oxide. It was assigned to the coupling site for Na+ transport. The mode of energy coupling of redox-driven Na+ pump was compared with those of decarboxylase- and ATP-driven Na+ pumps found in other bacteria.
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PMID:Sodium-transport NADH-quinone reductase of a marine Vibrio alginolyticus. 268 59


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