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)

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. Submitochondrial particles from Neurospora strain inl-89601 have been analyzed by electron spin resonance spectroscopy (ESR). Numerous signals due to iron-sulfur proteins are observed at low temperatures. Analysis of these ESR signals at various temperatures allows the assignment of resonances to iron-sulfur centers 1-5 that have been described in other organisms. There are no discrepancies between the signals seen in Neurospora and those described in other organisms and it is likely that Neurospora mitochondria contain the same iron-sulfur centers that are observed elsewhere. 2. NADPH and NADH act to reduce the iron-sulfur centers of respiratory complex I. 3. The drug pyrrolnitrin [3-chloro-4-(2'-nitro-3'-chlorphenyl)pyrrole] is an effective inhibitor of both NADH-supported and succinate-supported electron transport in Neurospora. 4. Analysis of pyrrolnitrin inhibition curves, respiration studies, ESR spectra, and the steady-state level of reduction of cytochrome b in the presence and absence of the drug shows that pyrrolnitrin acts to inhibit electron transport in Neurospora mitochondria at multiple sites in the region between ubiquinone and cytochrome b.
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PMID:Electron spin resonance investigations of mitochondrial electron transport in Neurospora crassa. Characterization of paramagnetic intermediates in a standard strain. 1 65

1. The electron paramagnetic resonance spectra at 15 K of reduced membrane particles of Paracoccus denitrificans exhibit resonance signals with g values, line shapes and temperature profile which are similar to the signals of the iron-sulfur centers observed in the NADH-ubiquinone segment of mitochondrial respiratory chains. These iron-sulfur centers are reducible with NADH, NADPH as well as chemically with dithionite. 2. Sulphate-limited growth of Paracoccus denitrificans results in the loss of an electron paramagnetic resonance signal (gz approximately 2.05, gy approximately gx approximately 1.92) which has properties similar to those of iron-sulfur center 2 of the NADH dehydrogenase of mitochondrial origin. The loss of this signal is accompanied by a decrease in the NADH oxidase and NADH ferricyanide oxidoreductase activities to respectively 30 and 40% of the values found for succinate-limited growth conditions. In addition respiration in membrane particles from sulphate-limited cells loses its sensitivity to rotenone. 3. Since sulphate-limited growth of Paracoccus denitrificans induces loss of site I phosphorylation [Arch. Microbiol. (1977) 112, 25-34] these observations suggest a close correlation between site I phosphorylation, rotenone-sensitivity and the presence of an electron paramagnetic resonance signal with gz approximately 2.05 and gy approximately gx approximately 1.92.
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PMID:The role of iron-sulfur center 2 in electron transport and energy conservation in the NADH-ubiquinone segment of the respiratory chain in Paracoccus denitrificans. 20 53

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

Energization of the pyridine nucleotide transhydrogenase in everted membrane vesicles from Escherichia coli JM83 was compared with the process in vesicles of the same strain transformed with the plasmid pDC21 overexpressing this enzyme. Proton translocation was assayed by the quenching of the fluorescence of the probe quinacrine. Agents able to discharge transmembrane proton gradients such as nigericin and the uncouplers 3,3',4',5-tetrachlorosalicylanilide and carbonyl cyanide m-chlorophenylhydrazone inhibited ATP-dependent transhydrogenation of NADP by NADH and discharged transmembrane proton gradients generated by transhydrogenation of AcNAD by NADPH, by oxidation of NADH, and by hydrolysis of ATP. This was observed in everted membrane vesicles of both strains JM83 and JM83pDC21. These strains differed significantly in the response of the NADH oxidation-dependent transhydrogenase. This reaction was inhibited by nigericin and uncouplers in membrane vesicles of JM83 but there was little inhibition or the reaction was stimulated in JM83pDC21, in spite of the discharge of the NADH oxidation-generated proton gradient measured by quinacrine fluorescence in the latter strain. It is proposed that the transhydrogenase is energized by direct or local (nonbulk phase) proton translocation in membranes of this strain. Uncouplers might facilitate these routes but would not discharge them. The generality of these observations was shown using other strains. NADH oxidase activity was severalfold lower in membrane vesicles of JM83pDC21 compared with JM83. The levels of ubiquinone and cytochromes, and the activities of NADH dehydrogenases I and II, and of cytochrome oxidase, were similar in the two strains. It is concluded that the NADH oxidase activity of JM83pDC21 is low because of the reduced rate of collision between electron-transferring complexes of the respiratory chain due to the large amount of transhydrogenase protein in the membranes of this strain. The large amount of transhydrogenase favors direct, nonbulk phase proton transfer. Transhydrogenase activity was stimulated by Ca2+, Mg2+, or Mn2+.
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PMID:Anomalous effect of uncouplers on respiratory chain-linked transhydrogenation in Escherichia coli membranes: evidence for a localized proton pathway? 131 Nov 61

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

The presence of redox systems in microsomes of brown adipose tissue (BAT) in cold exposed rats was investigated and compared with liver. BAT microsomes showed high activity of lipid peroxidation measured both by the formation of malondialdehyde (MDA) and by oxygen uptake. NADH and NADPH dependent cytochrome c reductase activity were present in both BAT and liver microsomes. Aminopyrine demethylase and aniline hydroxylase activities, the characteristic detoxification enzymes in liver microsomes could not be detected in BAT microsomes. BAT minces showed very poor incorporation of [1-14C]acetate and [2-14C]mevalonate in unsaponifiable lipid fraction compared to liver. Biosynthesis of cholesterol and ubiquinone, but not fatty acids, and the activity of 3-hydroxy-3-methyl glutaryl CoA reductase appear to be very low in BAT. Examination of difference spectra showed the presence of only cytochrome b5 in BAT microsomes. In addition to the inability to detect the enzyme activities dependent on cytochrome P-450, a protein with the characteristic spectrum, molecular size in SDS-PAGE and interaction with antibodies in double diffusion test, also could not be detected in BAT microsomes. The high activity of lipid peroxidation in microsomes, being associated with large oxygen uptake and oxidation of NADPH, will also contribute to the energy dissipation as heat in BAT, considered important in thermogenesis.
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PMID:Microsomal redox systems in brown adipose tissue: high lipid peroxidation, low cholesterol biosynthesis and no detectable cytochrome P-450. 210 21

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

NADH-ubiquinone reductase of bovine heart submitochondrial particles as prepared is unable to catalyze either the direct or reverse electron transfer from NADH to ubiquinone. The deactivated state of the enzyme in coupled particles was revealed as: (i) the absence of the rotenone-sensitive, delta mu H(+)-dependent succinate-ferricyanide reductase activity; (ii) a prominent lag in the aerobic succinate-supported, delta mu H(+)-dependent NAD+ reduction; and (iii) a lag in the rotenone-sensitive NADH-ubiquinone reductase or NADH oxidase activities. Being inactive as NADH-ubiquinone reductase (direct or reverse), the enzyme is fully active as rotenone-insensitive NADH-ferricyanide reductase. The enzyme can be activated by preincubation with substrates (NADH or NADPH) only under the conditions where the turnover of the NADH-ubiquinone reductase reaction (but not in the NADH-ferricyanide reductase) occurs. Partial activation of the enzyme was observed when the particles were preincubated with rotenone. Neither NADH under the conditions when the ubiquinone pool was reduced nor succinate plus delta mu H+ or dithionite were able to activate the enzyme. Once activated, the enzyme remains in the active state for quite a long time (more than 5 h at 0 degree C). The deactivation rate is extremely temperature-dependent, being insensitive to NAD+, ferricyanide or succinate. A comparison of the enzyme activation/deactivation kinetics showed that the same mechanism is involved in the slow activation of the direct and reverse electron transfer from NADH to ubiquinone. Activated particles catalyze the aerobic delta mu H(+)-dependent succinate-supported reverse electron transfer in the absence of ATP at a rate comparable with that of NADH-ubiquinone reductase.
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PMID:Slow active/inactive transition of the mitochondrial NADH-ubiquinone reductase. 211 5


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