Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:Q16795 (ubiquinone)
 5,455 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Chromatophores from Rhodospirillum rubrum were oriented as multilayers on quartz slides under reducing conditions. Irradiation of these multilayers in the resonance cavity of an ESR spectrometer at 6 K yielded the spectrum of the bacteriochlorophyll dimer triplet. The relative intesities of the main six lines of the triplet were dependent on the angle subtended by the direction of the external magnetic field with plane of the multilayers. The angular dependence of the intensities of these transitions can best be interpreted in terms of one of the principal axes of the triplet lying along the plane of the membrane while the other two axes are titled 10--20 degrees away from the parallel to and normal to the membrane directions. If we assume the porphyrin planes of the dimer to be parallel and the largest splitting of the triplet transitions to correspond to those transitions in a direction normal to this plane, then these data imply that the dimer planes are nearly perpendicular to the membrane plane. Purified iron-depleted phototrap complexes were similarly oriented in reconstituted phosphatidylcholine multilayers and the angular dependence of the light-induced spectrum recorded at room temperature. A computer analysis of this angular dependence suggests that the plane of the primary ubiquinone acceptor molecule is parallel to the plane of the membrane and therefore perpendicular to the donor.
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PMID:Orientation of the bacteriochlorophyll triplet and the primary ubiquinone acceptor of Rhodospirillum rubrum in membrane multilayers determined by ESR spectroscopy (I). 22 9

In reaction centers and chromatophores of photosynthetic bacteria strong light-induced emissive ESR signals have been found, not only after a flash but also under continuous illumination. The signal, with g = 2.0048 and delta Hpp = 7.6 G, is only present under reducing conditions in material in which the primary acceptor, ubiquinone, U and its associated high-spin ferrous ion are magnetically uncoupled. its amplitude under continuous illumination is strongly dependent on light intensity and on microwave power. The emissive signal is attributed to the prereduced primary acceptor, U-, which becomes polarized through transfer of spin polarization by a magnetic exchange interaction with the photoreduced, spin polarized intermediary acceptor, I-. A kinetic model is presented which explains the observed dependence of emissivity on light intensity and microwave power. Applying this analysis to the light saturation data, a value of the exchange rate between I- and U- of 4.10(8) s-1 is derived, corresponding to an exchange interaction of 3--5 G.
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PMID:Transfer of light-induced electron-spin polarization from the intermediary acceptor to the prereduced primary acceptor in the reaction center of photosynthetic bacteria. 22 14

Ubiquinones and tocopherols (vitamin E) are intrinsic lipid components which have a stabilizing function in many membranes attributed to their antioxidant activity. The antioxidant effects of tocopherols are due to direct radical scavenging. Although ubiquinones also exert antioxidant properties the specific molecular mechanisms of their antioxidant activity may be due to: (i) direct reaction with lipid radicals or (ii) interaction with chromanoxyl radicals resulting in regeneration of vitamin E. Lipid peroxidation results have now shown that tocopherols are much stronger membrane antioxidants than naturally occurring ubiquinols (ubiquinones). Thus direct radical scavenging effects of ubiquinols (ubiquinones) might be negligible in the presence of comparable or higher concentrations of tocopherols. In support of this our ESR findings show that ubiquinones synergistically enhance enzymic NADH- and NADPH-dependent recycling of tocopherols by electron transport in mitochondria and microsomes. If ubiquinols were direct radical scavengers their consumption would be expected. Further proving our conclusion HPLC measurements demonstrated that ubiquinone-dependent sparing of tocopherols was not accompanied by ubiquinone consumption.
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PMID:Antioxidant effects of ubiquinones in microsomes and mitochondria are mediated by tocopherol recycling. 211 8

In the present study we have used beef heart submitochondrial preparations (BH-SMP) to demonstrate that a component of mitochondrial Complex I, probably the NADH dehydrogenase flavin, is the mitochondrial site of anthracycline reduction. During forward electron transport, the anthracyclines doxorubicin (Adriamycin) and daunorubicin acted as one-electron acceptors for BH-SMP (i.e. were reduced to semiquinone radical species) only when NADH was used as substrate; succinate and ascorbate were without effect. Inhibitor experiments (rotenone, amytal, piericidin A) indicated that the anthracycline reduction site lies on the substrate side of ubiquinone. Doxorubicin and daunorubicin semiquinone radicals were readily detected by ESR spectroscopy. Doxorubicin and daunorubicin semiquinone radicals (g congruent to 2.004, signal width congruent to 4.5 G) reacted avidly with molecular oxygen, presumably to produce O2-, to complete the redox cycle. The identification of Complex I as the site of anthracycline reduction was confirmed by studies of ATP-energized reverse electron transport using succinate or ascorbate as substrates, in the presence of antimycin A or KCN respiratory blocks. Doxorubicin and daunorubicin inhibited the reduction of NAD+ to NADH during reverse electron transport. Furthermore, during reverse electron transport in the absence of added NAD+, doxorubicin and daunorubicin addition caused oxygen consumption due to reduction of molecular oxygen (to O2-) by the anthracycline semiquinone radicals. With succinate as electron source both thenoyltrifluoroacetone (an inhibitor of Complex II) and rotenone blocked oxygen consumption, but with ascorbate as electron source only rotenone was an effective inhibitor. NADH oxidation by doxorubicin during BH-SMP forward electron transport had a KM of 99 microM and a Vmax of 30 nmol X min-1 X mg-1 (at pH 7.4 and 23 degrees C); values for daunorubicin were 71 microM and 37 nmol X min-1 X mg-1. Oxygen consumption at pH 7.2 and 37 degrees C exhibited KM values of 65 microM for doxorubicin and 47 microM for daunorubicin, and Vmax values of 116 nmol X min-1 X mg-1 for doxorubicin and 114 nmol X min-1 X mg-1 for daunorubicin. In marked contrast with these results, 5-iminodaunodrubicin (a new anthracycline with diminished cardiotoxic potential) exhibited little or no tendency to undergo reduction, or to redox cycle with BH-SMP. Redox cycling of anthracyclines by mitochondrial NADH dehydrogenase is shown, in the accompanying paper (Doroshow, J. H., and Davies, K. J. A. (1986) J. Biol. Chem. 261, 3068-3074), to generate O2-, H2O2, and OH which may underlie the cardiotoxicity of these antitumor agents.
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PMID:Redox cycling of anthracyclines by cardiac mitochondria. I. Anthracycline radical formation by NADH dehydrogenase. 345 45

Iron-sulfur clusters present in rat liver submitochondrial particles were characterized by ESR at temperatures between 30 and 5.5 K combined with potentiometric titrations. The spectral and thermodynamic characteristics of the iron-sulfur clusters were generally similar to those previously reported for pigeon or bovine heart submitochondrial particles. Clusters N-1a, N-1b, N-2, N-3 and N-4 of NADH dehydrogenase had midpoint oxidation-reduction potentials at pH 7.5 of -425, -265, -85, -240 and -260 mV, respectively. Clusters S-1 and S-3 of succinate dehydrogenase had midpoint potentials of 0 and +65 mV, respectively. The iron-sulfur cluster of electron-transferring flavo-protein-ubiquinone oxidoreductase exhibited the gz signal at g = 2.08 and had a midpoint potential of +30 mV. This signal was relatively prominent in rat liver compared to pigeon or bovine heart. Submitochondrial particles from rats chronically treated with ethanol (36% of total calories, 40 days) showed decreases of 20-30+% in amplitudes of signals due to clusters N-2, N-3 and N-4 compared to those from pair-fed control rats. Signals from clusters N-1b, S-1, S-3 and electron-transferring flavoprotein-ubiquinone oxidoreductase were unaffected. Microwave power-saturation behavior was similar for both submitochondrial particle preparations, suggesting that the lower signal amplitudes reflected a lower content of these particular clusters. NADH dehydrogenase activity was significantly decreased (46%), whilst succinate dehydrogenase activity was elevated (25%), following chronic ethanol consumption. The results indicate that chronic ethanol treatment leads to an alteration of the structure and function of the NADH dehydrogenase segment of the electron transfer chain. This alteration is one of the factors contributing to the lower respiration rates observed following chronic ethanol administration.
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PMID:Characterization of iron-sulfur clusters in rat liver submitochondrial particles by electron paramagnetic resonance spectroscopy. Alterations produced by chronic ethanol consumption. 624 7

Mitochondrial NADH-ubiquinone oxidoreductase (Complex I) is a lipoprotein enzyme containing phosphatidylcholine (PC), phosphatidylethanolamine (PE) and cardiolipin. Enzyme preparations containing endogenous cardiolipin and a range of either soyabean PC or dimyristoylphosphatidylcholine (DMPC) concentrations have been made. Using a spin-labelled fatty acid, two probe environments differing in mobility have been shown to be present. The fatty acid probe has a relative binding constant (or partition coefficient between lipid and protein) of unity. The boundary layer or lipid annulus reported by the probe has a value of approx. 300 lipid molecules per molecule of enzyme FMN in preparations containing soyabean PC, or DMPC above the phase transition temperature of the latter. In soyabean PC-replaced enzyme the apparent size of the boundary layer is independent of temperature between 30 degrees C and 14 degrees C but shows a modest increase to about 400 lipid molecules per molecule of FMN between 14 degrees C and 2 degrees C. Complex I replaced with high concentrations of DMPC gives non-linear Arrhenius plots of NADH-ubiquinone oxidoreductase activity. The results of the ESR experiments show that both boundary layer and bulk lipid must be motionally restricted for this to occur. Thus, the change in activity is probably not caused by an effect exerted directly on the catalytic activity of the enzyme but is more likely due to restriction of free diffusion of ubiquinone to its site of reduction.
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PMID:A spin label study of the lipid boundary layer of mitochondrial NADH-ubiquinone oxidoreductase. 629 75

NADH-ubiquinone oxidoreductase (Complex I) can be recombined with ubiquinol-cytochrome c oxidoreductase (Complex III) to reconstitute NADH-cytochrome c oxidoreductase. Two modes of interaction have been found. In one, the Complexes interact stoichiometrically in one to one molar ratios to give a binary Complex I-III unit. In the other, the kinetics of NADH-cytochrome c oxidoreductase are characteristic of 'Q-pool' behaviour seen in intact mitochondria and submitochondrial particles in which the Complexes need not interact directly but can do so via a pool of mobile ubiquinone. Stoichiometric behaviour is found when only boundary layer or annular lipid is present or the lipid is in the gel phase. The lipid is immobile on the ESR time scale and protein rotational diffusion, measured by saturation transfer ESR, is very slow. Q-pool behaviour is found when mobile extra-annular lipid phase is also present. Protein rotational diffusion is rapid and characteristic of a fully disaggregated state. We have also used freeze-fracture electron microscopy of reconstituted NADH-cytochrome c oxidoreductase to monitor protein aggregation and lateral phase separation of lipids and proteins under various conditions. We discuss our findings in relation to models for lateral interactions between respiratory chain enzymes.
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PMID:The effects of lipid fluidity on the rotational diffusion of complex I and complex III in reconstituted NADH-cytochrome c oxidoreductase. 629 76

It was shown that gamma-radiation (8-16 Gy) did not influence the number of paramagnetic centers of hemal (g = 2.42, g = 2.25) and nonhemal (g = 1.94) iron of rat tissues: free radicals were significantly reduced 5 min after 16 Gy irradiation. The combined effect of gamma-radiation (8 Gy) and ubiquinone-9 decreased the number of the above-mentioned ESR signals after 48 h. The number of free radicals in the rat liver, kidneys and spleen was almost twice reduced 28 days following castration. The administration of methyl testosterone increased the free radical amount in the heart and was ineffective in other rat organs.
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PMID:[Free radicals and metal paramagnetic ions of the tissues of rats exposed to gamma irradiation and hormones]. 630 17

Superoxide-driven reduction of alpha-tocopheroxyl radical in the presence of ubiquinone-10 has been demonstrated in dimethylsulfoxide. Our HPLC measurements showed that ubiquinone-10 protected alpha-tocopherol against oxidation by KO2 in a concentration-dependent manner. alpha-Tocopherol was oxidized by KO2 to form ESR-detectable radicals of tocopherol ubisemiquinone. In the presence of ubiquinone-10, neither these radicals nor alpha-tocopheroxyl radicals (generated by uv light or PbO2) could be detected in ESR spectra. Instead, ESR signals of ubisemiquinone-10 radicals were observed. Formation of ubisemiquinone-10 radicals from ubiquinone-10 upon addition of KO2 was ascertained by their characteristic ESR and uv-vis spectra. alpha-Tocopherol caused a concentration-dependent decrease of the ubisemiquinone-10 radical steady-state concentration. We conclude that one-electron reduction of ubiquinone-10 by superoxide ion resulting in the formation of ubiquinone-10 radicals caused redox-cycling of alpha-tocopherol from its phenoxyl radical, thus preventing loss of alpha-tocopherol. This suggests that coenzyme Q may have another physiological function, i.e., protection of alpha-tocopherol against superoxide-driven oxidation.
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PMID:Ubiquinone-dependent recycling of vitamin E radicals by superoxide. 748 97

The interaction between ubiquinones and vitamin E was studied in the inner membranes of rat liver mitochondria, liposomes and human erythrocyte plasma membranes. Free radicals were produced by addition of exogenous oxidants, and their reaction with chromanols and ubiquinone was followed by ESR and HPLC. Membranes were made deficient in ubiquinone but sufficient in alpha-tocopherol and were reconstituted with added ubiquinone. With these membrane preparations it was shown that (i) in the inner mitochondrial membranes there is a requirements for ubiquinone in the enzymatic recycling of vitamin E; (ii) succinate-ubiquinone reductase incorporated in liposomes cannot protect vitamin E in the absence of ubiquinone and (iii) in human erythrocyte plasma membranes protection against the loss of vitamin E can be provided by NADH-cytochrome-b5-dependent enzymatic recycling. We conclude that ubiquinonols (ubisemiquinones) reduce vitamin E through electron transport.
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PMID:Interactions between ubiquinones and vitamins in membranes and cells. 775 45


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