Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:Q8NEX9 (reductase)
 26,410 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. At 21 degrees C incubation of NADH-ubiquinone-1 reductase (Complex 1) with trypsin caused selective inhibition of nicotinamide nucleotide transhydrogenase activity. The reduction of K3Fe(CN)6 by NADH or NADPH was unaffected, but a slow decrease in the rate of reduction of ubiquinone-1 by NADH was observed. 2. The pH-dependence of nicotinamide nucleotide transhydrogenase activity differed in Complex I and trypsin-treated Complex I. The trypsin-labile activity had a pH optimum of approx. 6.5, whereas the trypsin-resistant activity had a pH optimum of approx. 5.5 or less. 3. The trypsinlabile transhydrogenase activity was specifically inhibited by butanedione or phenylglyoxal and was identified with the enzyme catalysing energy-linked transhydrogenase activity in submitochondrial particles. 4. Polyacrylamide-gel electrophoresis in the presence of sodium dodecyl sulphate revealed that trypsin caused degradation of a polypeptide of mol.wt 20500 in parallel with the loss of transhydrogenase activity. 5. At 30 degrees C and higher trypsin concentrations, the rate of reduction of K3Fe(CN)6 by NADH or NADPH slowly decreased. Increased lability of NADH-K3Fe(CN)6 reductase activity to trypsin was observed when the endogenous phospholipid of Complex I was depleted by detergent or phospholipase A treatment. 6. Polyacrylamide-gel electrophoresis indicated that removal of phospholipid allowed much more extensive degradation of constituent polypeptides by trypsin. The subunits of the low-molecular-weight (type II) dehydrogenase (53000 and 26000 mol.wt.) were, however, relatively resistant to trypsin even in phospholipid-depleted preparations.
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PMID:The effects of proteolytic digestion by trypsin on the structure and catalytic properties of reduced nicotinamide-adenine dinucleotide dehydrogenase from bovine heart mitochondria. 0 40

1. The activities of the soluble reconstitutively active succinate dehydrogenase (EC 1.3.99.1) measured with three artificial electron acceptors, e.g. ferricyanide, phenazine methosulfate and free radical of N,N,N',N'-tetramethyl-p-phenylenediamine (WB), have been compared. The values estimated by extrapolation to infinite acceptor concentration using double reciprocal plots 1/v versus 1/[acceptor] are nearly the same for ferricyanide and phenazine methosulfate and about twice as high for the WB. 2. The double reciprocal plots 1/v versus 1/[succinate] in the presence of malonate at various concentrations of WB give a series of straight lines intercepting in the third quadrant. The data support the mechanism of the overall reaction, in which the reduced enzyme is oxidized by WB before dissociation of the enzyme-product complex. 3. The dependence of the rate of the overall reaction on WB concentration shows that only one kinetically significant redox site of the soluble succinate dehydrogenase is involved in the reduction of WB. 4. Studies of the change of V and Km values during aerobic inactivation of the soluble enzyme suggest that only 'the low Km ferricyanide reactive site' (Vinogradov, A.D., Gavrikova, E.V. and Goloveshkina, V.G. (1975) Biochem. Biophys, Res. Commun. 65, 1264--1269) is involved in reoxidation of the reduced enzyme by WB. 5. The pH dependence of V for the succinate-WB reductase reaction shows that the group of the enzyme with the pKa value of 6.7 at 22 degrees C is responsible for the reduction of dehydrogenase in the enzyme-substrate complex. 6. When WB interacts with the succinate-ubiquinone region of the respiratory chain, the double reciprocal plot 1/v versus 1/[WB] gives a straight line. The thenoyltrifluoroacetone inhibition of succinate-ubiquinone reductase or extraction of ubiquinone alter the 1/v versus 1/[WB] plots for the curves with a positive initial slope intercepting the ordinate at the same V as in the native particles. The data support the mechanism of succinate-ubiquinone reduction, in which no positive modulation of succinate dehydrogenase by ubiquinone exist in the membrane.
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PMID:Studies on the succinate dehydrogenating system. I. Kinetics of the succinate dehydrogenase interaction with a semiquindiimine radical of N,N,N',N'-tetramethyl-p-phenylenediamine. 3 33

Exposure of rats to hypobaric stress for periods of up to 36 h caused a consistent change in the succinate-NT reductase activity of the heart mitochondria whereas there was no significant change in the activities of either succinate dehydrogenase and succinate-NT reductase of the brain and the kidney. Mitochondrial succinate dehydrogenase of the heart, the brain and the kidney was activated 2- to 7-fold with the substrate and malonate. The activations obtained with oxalate, citrate and dinitrophenol were relatively lower in comparison to succinate and malonate. Benzohydroquinone and 2-nitrophenol had no stimulatory effect on the heart, the brain and the kidney mitochondria. THE ACTIVATIONS OBTAINED WITH THE VARIOUS EFFECTORS PARTIALLY (OR COMPLETELY IN THE CASE OF SUCCINATE) REVERSED ON WASHING THE MITOCHONDRIAL SAMPLES WITH THE SUCROSE HOMOGENIZING MEDIUM. The effect of ubiquinol, which also activated the enzyme, was only partially reversed after the second preincubation with succinate in the brain and the kidney whereas in the heart the activity was fully reversed. The increased activity of succinate dehydrogenase obtained with ATP and ADP was further enhanced by Mg2+ exclusively in the brain mitochondria, suggesting the possibility of Mg2+-AIP complex as the active species. Succinate-NT reductase of the heart, the brain and the kidney mitochondria showed a high activation with ubiquinone whereas its reduced form had no stimulatory effect.
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PMID:Oxidation of succinate in heart, brain, and kidney mitochondria in hypobaria and hypoxia. 16 66

We have examined the thermodynamic properties of the physiological electron donor to ferricytochrome c2 in chromatophores from the photosynthetic bacterium Rhodopseudomonas sphaeroides. This donor (Z), which is capable of reducing the ferricytochrome with a halftime of 1-2 ms under optimal conditions, has an oxidation-reduction midpoint potential of close to 150 mV at pH 7.0, and apparently requires two electrons and two protons for its equilibrium reduction. The state of reduction of Z, which may be a quinone.protein complex near the inner (cytochrome c2) side of the membrane, appears to govern the rate at which the cyclic photosynthetic electron transport system can operate. If Z is oxidized prior to the flash-oxidation of cytochrome c2, the re-reduction of the cytochrome takes hundreds of milliseconds and no third phase of the carotenoid bandshift occurs. In contrast if Z is reduced before flash activation, the cytochrome is rereduced within milliseconds and the third phase of the carotenoid bandshift occurs. The prior reduction of Z also has a dramatic effect on the uncoupler sensitivity of the rate of electron flow; if it is oxidized prior to activation, uncoupler can stimulate the cytochrome rereduction after several turnovers by less than tenfold, but if it is reduced prior to activation, the stimulation after several turnovers can be as dramatic as a thousandfold. The results suggest that Z plays a central role in controlling electron and proton movements in the ubiquinone cytochrome b-c2 oxido-reductase.
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PMID:Single and multiple turnover reactions in the ubiquinone-cytochrome b-c2 oxidoreductase of Rhodopseudomonas sphaeroids: the physical chemistry of the major electron donor to cytochrome c2, and its coupled reactions. 20 11

Hydroxylation of benz/a/pyrene might occur under decreased activity of NADPH-dependent reductase. In vivo a decrease in the activity of NADPH-dependent reductase did not influence apparently the intensity of benz/a/pyrene hydroxylation, which is maintained due to redistribution of reducing equivalents between oxygenase and oxidase systems in the cells. Anticarcinogenic effects of two different substances chrisene and ubiquinone are discussed taking into account possible normalization of NADPH- and NADH-dependent oxidative reactions in the cells.
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PMID:[Distribution of the reducing equivalents in the cell in the active phase of benz(a)pyrene metabolism]. 22 98

The effect of ubiquinones with different length of their chain (CoQ0, CoQ1, CoQ2, CoQ6, CoQ9) and their synthetic analogues (analogues of ubiquinone-1, hexahydroubiquinone-4, monophytylquinone, diphytylquinone, triphytylquinone) on the activity of ubiquinone dependent enzyme systems was studied in mitochondrial fractions from the yeast Candida guilliermondii. All of the ubiquinone homologues studied activated these systems. The synthetic analogues of ubiquinone nonspecifically inhibited the activity of NADH2-oxidase system. The inhibition was reversible when CoQ0 and CoQ1, but not CoQ6 and CoQ9, were added to the system. In the succinate-CoQ-reductase system, the inhibition caused by the analogues of ubiquinone was eliminated when all of the tested homologues were added to the system. In contrast to other analogues of ubiquinone, hexahydroubiquinone-4 was an inhibitor for the NADH2-oxidase system and an activator for the succinate-CoQ-reductase system, and eliminated the inhibiting action of other ubiquinone analogues in this system. Similar action of ubiquinone homologues was shown in the elimination of the inhibition of ubiquinone dependent systems caused by the specific inhibitors of electron transport, viz. rotenone and antimycin A.
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PMID:[Effect of ubiquinones and their analogs on the respiratory chain enzyme activity of Candida guilliermondii yeasts]. 53 Jan 41

A strain carrying a point mutation affecting the NADH dehydrogenase complex of Escherichia coli has been isolated and its properties examined. The gene carrying the mutation (designated ndh) was located on the E. coli chromosome at about minute 23 and was shown to be cotransducible with the pyrC gene. Strain carrying the ndh- allele were found to be unable to grow on mannitol and to grow very poorly on glucose unless the medium was supplemented with succinate, acetate or casamino acids. The following properties of strains carrying the ndh- allele were established which suggest that the mutation affects the NADH dehydrogenase complex but apparently not the primary dehydrogenase. Membrane preparations possess normal to elevated levels of D-lactate oxidase and succinate oxidase activities but NADH oxidase is absent. NADH is unable to reduce ubiquinone in the aerobic steady state and reduces cytochrome b very slowly when the membranes become anaerobic. NADH dehydrogenase, measured as NADH-dichlorophenolindophenol reductase is reduced but not absent. NADH oxidase is stimulated by menadione although not by Q-3 or MK-1 and in the presence of menadione, cytochrome b is reduced normally by NADH. Further mutants affected in NADH oxidase were isolated using a screening procedure based on the growth characteristics of the original ndh- strain. The mutantions carried by these strains were all cotransducible with the pyrC gene and the biochemical properties of the additional mutants were similar to those of the original mutant. The properties of the group of ndh- mutants established so far suggest that they are affected in the transfer of reducing equivalents from the NADH dehydrogenase complex to ubiquinone.
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PMID:Mutations affecting the reduced nicotinamide adenine dinucleotide dehydrogenase complex of Escherichia coli. 79 16

The methyltransferase responsible for the conversion of 5-demethylubiquinone-9 to ubiquinone-9 in rat liver mitochondria has been shown to be localized in the inner membrane of rat liver mitochondria. NADH was required to generate the hydroquinone, which was the immediate substrate for methylation. The Km for 5-demethylubiquinone-9 was estimated to be in the range of 60 to 80 nM and the Km for S-adenosylmethionine was found to be 22 micronM. The methyl-transferase was solubilized by Triton X-100, a procedure which inactivated the 5-demethylubiquinone-9 reductase. Dithionite was found to partially substitute for NADH in both membranous and soluble systems. Inhibitors of catechol-O-methyltransferase were not effective inhibitors of 5-demethylubiquinone-9-methyltransferase. In addition, catechol-O-methyltransferase and 5-demethylubiquinone-9-methyltransferase were found to have reciprocal subcellular localizations. It is likely that the hydrophobic side chain of ubiquinone, added to p-hydroxybenzoate in the first biosynthetic step, is required for attachment to the lipid bilayer. This permits subsequent metabolism of the ring system by membrane-bound enzymes, including the final methylation to form ubiquinone-9.
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PMID:5-demethylubiquinone-9-methyltransferase from rat liver mitochondria. Characterization, localization, and solubilization. 86 14

The activity of ubiquinone-dependent enzyme systems was studied in mitochondrial fractions of the yeast Candida guilliermondii cultivated on the medium containing carbohydrates of hydrocarbons as a source of carbon. The activity of NADH2-oxidase and succinate-CoQ-reductase was higher in systems with mitochondrial fractions from the cells grown on the medium with n-paraffins than in mitochondrial fractions from the cells cultivated on the medium with glucose. About 30% of intracellular ubiquinone is located in the mitochondrial fraction of hydrocarbon oxidizing yeast cells; however, the activity of enzymes was stimulated upon introduction of exogeneous ubiquinones into the systems. Therefore, exogeneous ubiquinones may be involved in the electron transport chain during oxidation of reduced substrates. Both ubiquinone-dependent enzyme systems are resistant to storage.
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PMID:[Localization of ubiquinone-9 in electron transport chain of Candida guilliermondii]. 100 42

When incubated in an air atmosphere, solubilized succinate dehydrogenase (succinate:(acceptor) oxidoreductase, EC 1.3.99.1) quickly loses the capability to recombine with membrane components to catalyze mitochondrial related electron transport activities. At 0 degrees the loss in reconstitution capability is a first-order process; the half-life of the enzyme is 1.6 hr at this temperature. The enzyme is stabilized by recombining it with submitochondrial particles or with a cytochrome b preparation-phospholipid mixture. The presence of the cytochrome b preparation in the succinate dehydrogenase-cytochrome b-phospholipid complex is obligatory, indicating that protein-protein interactions between succinate dehydrogenase and other membrane components are important in stabilizing the capability of the flavoprotein to transfer electrons to other respiratory components. Treatment of this complex with phospholipase C results in loss of most of the succinate-dichlorophenolindophenol reductase activity and almost complete hydrolysis of phospholipid. Succinate dehydrogenase maintains its capability to participate in mitochondrial electron transport for several hours if the phospholipase treated complex is reconstituted with lysolecithin at the time of assay. Phospholipids are therefore not required for the stabilization process, but rather for formation of an active reductase complex. A lipophilic environment, if required for stabilization, can be provided by diglycerides. Diglycerides also can provide an environment conducive to electron transfer from succinate to ubiquinone but do so less efficiently than intact phospholipids.
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PMID:The role of protein and lipids in stabilizing the activity of bovine heart succinate dehydrogenase. 112 75


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