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Query: UNIPROT:Q16795 (ubiquinone)
 5,455 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. The relationship between chain composition and the efficiency of respiration-linked proton translocation was studied in nine bacterial species of widely differing taxonomic and ecological status. 2. All the bacteria investigated contained respiratory chain dehydrogenases, ubiquinone and/or menaquinone, cytochrome b and cytochrome oxidase aa3 and/or o. In addition, some of these organisms also contained pyridine nucleotide transhydrogenase and/or cytochrome c. 3. leads to H+/O ratios of whole cell suspensions oxidising endogenous substrates were in the approximate range 4-8 mol H+ translocated per g-atom oxygen consumed. It was concluded from the observed leads to H+/O ratios of cells loaded with specific substrates that proton-translocating loops 1 and 2 were present in all of the organisms investigated, but that loops 0 and 3 were dependent upon the presence of pyridine nucleotide transhydrogenase and cytochrome c respectively. 4. The wide range in energy conservation efficiency which was observed in these organisms is discussed in relation to their respiratory chain composition and natural habitat.
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PMID:Bacterial respiration-linked proton translocation and its relationship to respiratory-chain composition. 24 Jun 79

1. Whole cells of Methylomonas Pl1 contained ubiquinone, identified as ubiquinone-8. No naphthaquinone was detected. Ubiquinone was located predominantly in the particulate fraction, which also contained most of the NADH oxidase activity. 2. Aerobic incubation of cells with formaldehyde or methanol resulted in about 20% reduction of ubiquinone, irrespective of the presence or absence of dinitrophenol. On inhibition of the respiration by cyanide, ubiquinone became partly reduced by endogenous substrates (15--25%), and a further reduction occurred only in the presence of formaldehyde (up to 60%). When endogenous substrates were completely exhausted, then 44 and 23% of ubiquinone was reduced by formaldehyde or methanol respectively. 3. The difference spectra at room and liquid-N2 temperatures revealed the presence of cytochrome b and two cytochromes c (c-552.5 and c-549) all tightly bound to the membrane. Cytochrome c-552.5 was also found in the soluble fraction. 4. Redox changes of cytochromes b and c, with methanol or formaldehyde as substrates, respond to the aerobic and anaerobic states of the cell and to KCN inhibition in a manner characteristic of the electron carriers of the respiratory chain. 5. The merging point for electron transport from NADH dehydrogenase and formaldehyde dehydrogenase is suggested to be at the level of ubiquinone.
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PMID:The respiratory chain of a newly isolated Methylomonas Pl1. 41 43

The photophosphorylation systems of Rhodopseudomonas capsulata and Rhodospirillum rubrum chromatophores have been compared in respect to the effects of artificial electron carriers [N-methylphenazonium methosulfate (PMS) and diaminodurene], reducing agents (ascorbate in particular), and various quinones in the absence and presence of the electron transport inhibitors antimycin A and dibromothymoquinone (DBMIB). In addition, the effects of both inhibitors on photosynthetic electron transport through cytochromes b and c has been followed. From the results obtained, it appears that in both organisms: a) ubiquinone functions as an electron carrier between the cytochromes, and b) both antimycin A and DBMIB inhibit cyclic electron flow in the segment...cytochrome b leads to ubiquinone leads to cytochrome c..., but at different sites. The systems apparently differ mainly in respect to the nature of the electron flow by-pass "shunt" that is evoked in the presence of PMS; thus, in R. rubrum, PMS catalyzes a shunt that by-passes both cytochrome b and ubiquinone, whereas in Rps. capsulata the PMS shunt seems to circumvent only ubiquinone.
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PMID:A comparison of electron transport and photophosphorylation systems of Rhodopseudomonas capsulata and Rhodospirillum rubrum. Effects of antimycin A and dibromothymoquinone. 41 85

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 respiratory chain is a mosaic of complexes functionally linked through the mobile intermediates ubiquinone and cytochrome c. Changes in content of complexes that are not rat-limiting might not be reflected in the overall respiratory rate but may be revealed by titration with specific inhibitors. Oxidation of succinate by membranes of liver mitochondria from fetal, adult and starved rats was titrated with antimycin. Initial respiratory rates were similar but antimycin-titration curves were markedly different. The results indicate that the content of Complex III (cytochrome b-c1 span) is much lower in mitochondria from fetal and starved adult rats than in controls. In no case however is Complex III initially rat-limiting, and in fetal and starved adult rats it seems that a much lower content of functional Complex III is required to sustain a given respiratory rate. A possible explanation is a compensatory optimization of the pool function of ubiquinone, through increases in its content or its mobility in the mitochondrial membrane.
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PMID:Iron centres and rate-limiting spans in the respiratory chains of mitochondria from adult and fetal rats. 105 39

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

Mitochondrial function and structure in cirrhotic livers from humans or rats show a variety of changes as compared to control livers. Mitochondrial ATP production is reduced in rats with CCl4- or thioacetamide-induced liver cirrhosis and in rats with secondary biliary cirrhosis. Activity of the electron transport chain is decreased in rats with secondary biliary cirrhosis. In rats with CCl4-induced cirrhosis, the mitochondrial content of certain constituents of the respiratory chain (cytochrome a + a3, cytochrome b and ubiquinone) is increased and activities of cytochrome c oxidase and ATPase are elevated. Similarly, in humans with liver cirrhosis, mitochondrial cytochrome a + a3 content is elevated and has been used to assess the risk for hepatectomy. In rats with secondary biliary cirrhosis, compensatory strategies include increased mitochondrial volume per hepatocyte and possibly increased extramitochondrial ATP production (increased glycolysis). Thus, a variety of adaptive mechanisms are used to maintain mitochondrial function in cirrhotic livers.
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PMID:Adaptation of mitochondrial metabolism in liver cirrhosis. Different strategies to maintain a vital function. 129 65

The reduction of duroquinone (DQ) and 2,3-dimethoxy-5-methyl-6-decyl-1,4-benzoquinone (DB) by NADH and ethanol was investigated in intact yeast mitochondria with good respiratory control ratios. In these mitochondria, exogenous NADH is oxidized by the NADH dehydrogenase localized on the outer surface of the inner membrane, whereas the NADH produced by ethanol oxidation in the mitochondrial matrix is oxidized by the NADH dehydrogenase localized on the inner surface of the inner membrane. The reduction of DQ by ethanol was inhibited 86% by myxothiazol; however, the reduction of DQ by NADH was inhibited 18% by myxothiazol, suggesting that protein-protein interactions between the internal (but not the external) NADH: ubiquinone oxidoreductase and ubiquinol:cytochrome c oxidoreductase (the cytochrome bc1 complex) are involved in the reduction of DQ by NADH. The reduction of DQ and DB by NADH and ethanol was also investigated in mutants of yeast lacking cytochrome b, the iron-sulfur protein, and ubiquinone. The reduction of both quinone analogues by exogenous NADH was reduced to levels that were 10 to 20% of those observed in wild-type mitochondria; however, the rate of their reduction by ethanol in the mutants was equal to or greater than that observed in the wild-type mitochondria. Furthermore, the reduction of DQ in the cytochrome b and iron-sulfur protein lacking mitochondria was myxothiazol sensitive, suggesting that neither of these proteins is an essential binding site for myxothiazol. The mitochondria from the three mutants also contained significant amounts of antimycin- and myxothiazol-insensitive NADH:cytochrome c reductase activity, but had no detectable succinate:cytochrome c reductase activity. These results suggest that the mutants lacking a functional cytochrome bc1 complex have adapted to oxidize NADH.
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PMID:Direct interaction between the internal NADH: ubiquinone oxidoreductase and ubiquinol:cytochrome c oxidoreductase in the reduction of exogenous quinones by yeast mitochondria. 130 74

We report here some unusual properties of ubiquinol: cytochrome c reductase of eel and other fish mitochondria. The turnover rate of the reductase is clearly higher than in mammalian mitochondria and the binding constant for ubiquinone seems to be larger than in other vertebrates. Additionally, the reductase activity of fish mitochondria is resistant to some powerful inhibitors that bind to cytochrome b, in particular to funiculosin. After sequencing most of the gene of eel cytochrome b and comparing the deduced amino acid sequence with that of other fish and animals, we hypothesize that the decreased binding of funiculosin could be due to a few amino acid replacements in the third and fourth transmembrane helix of the protein. In particular, the presence of methionine instead of alanine at position 125 seems to be largely responsible for the strong resistance to funiculosin and also to the partial resistance to myxothiazol in all fish mitochondria. Correlations between some residue substitutions in cytochrome b and the different effects of funiculosin in different species are also considered.
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PMID:Cytochrome b of fish mitochondria is strongly resistant to funiculosin, a powerful inhibitor of respiration. 131 3

The tissutal concentrations of reduced glutathione (GSH) and the contents of some key components in the electron transfer chain (namely ubiquinone, cytochromes b, c1, c, and aa3) of the intraterminal mitochondria are measured in the forebrains from 20-, 60-, or 100-week-old Wistar rats. Moreover, in 60-week-old rats, the biochemical analyses are performed also 18 h after the induction of a peroxidative stress by cyclohexene-1-one. The rats have been i.p. pretreated for 8 weeks (7 days/week) with agents acting on macrocirculation (papaverine), carbohydrate metabolism (hopanthenate), lipid metabolism (phosphatidylcholine), energy transduction (theniloxazine), and dopaminergic system (dihydroergocriptine). Brain aging is characterized by the decrease in both GSH and mitochondrial cytochrome aa3, without changes in ubiquinone and cytochrome b populations. In the same way, the peroxidative stress induced by cyclohexene-1-one causes both a GSH depletion and an imbalance among the concentrations of the mitochondrial electron transfer carriers. Only cytochrome aa3 retains all the partially-reduced oxygen intermediates tightly bound to its active sites. Therefore, it is possible to hypothesize that an electron leakage at the level of the auto-oxidizing chain components (i.e., cytochrome b and ubiquinone populations) increases the release of activated oxygen species (superoxide radical, hydroxyl radical). The treatment with the quoted pharmacological tools suggests that GSH and mitochondrial electron transfer carriers are functionally linked, but not interdependent one another.
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PMID:The mitochondrial electron transfer alteration as a factor involved in the brain aging. 132 Jul 45


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