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PubMed1977

Aerobic respiration in mutants of Escherichia coli accumulating quinone analogues of ubiquinone.

The ability of three naturally occurring analogues of ubiquinone to function in aerobic respiration in Escherichia coli has been studied. The compounds, which differ from ubiquinone in terms of the substituents on the quinone ring, accumulate in the cytoplasmic membranes of ubiE-, ubiF- and ubiG- mutants. One of the analogues (2-octaprenyl-3-methyl-6-methoxy-1,4-benzoquinone, NMQ), which lacks the 5-methoxyl group of the benzoquinone ring of ubiquinone promoted the oxidation of NADH, D-lactate and alpha-glycerophosphate but not succinate. Electron transport supported by MMQ was found to be coupled to phosphorylation. In contrast, 2-octaprenyl-6-methoxy-1,4-benzoquinone, which lacks both the 3-methyl and 5-methoxyl groups of ubiquinone, and 2-octaprenyl-3-methyl-5-hydroxy-6-methoxy-1,4-benzoquinone, in which the 5-methoxyl group of ubiquinone is replaced by an hydroxyl group, were virtually inactive in the oxidases tested. The ability of MMQ to function in respiration in isolated membranes is consistent with the findings that the growth rate and yield of a ubiF- strain, unlike other ubi- strains, were only slightly lower than those of a ubiF+ strain. The fact that MMQ is active in some but not all oxidases provides further support for the concept that the quinones link the individual dehydrogenases to the respiratory chain and that each dehydrogenase has specific structural requirements for quinone acceptors.

Aerobiosis↗

PubMed1976

Role of ubiquinone in the mitochondrial generation of hydrogen peroxide.

Antimycin-inhibited bovine heart submitochondrial particles generate O2- and H2O2 with succinate as electron donor. H2O2 generation involves the action of the mitochondrial superoxide dismutase, in accordance with the McCord & Fridovich [(1969) j. biol. Chem. 244, 6049-6055] reaction mechanism. Removal of ubiquinone by acetone treatment decreases the ability of mitochondrial preparations to generate O2- and H2O2, whereas supplementation of the depleted membranes with ubiquinone enhances the peroxide-generating activity in the reconstituted membranes. Addition of superoxide dismutase to ubiquinone-reconstituted membranes is essential in order to obtain maximal rates of H2O2 generation since the acetone treatment of the membranes apparently inactivates (or removes) the mitochondrial superoxide dismutase. Parallel measurements of H2O2 production, succinate dehydrogenase and succinate-cytochrome c reductase activities show that peroxide generation by ubiquinone-supplemented membranes is a monotonous function of the reducible ubiquinone content, whereas the other two measured activities reach saturation at relatively low concentrations of reducible quinone. Alkaline treatment of submitochondrial particles causes a significant decrease in succinate dehydrogenase activity and succinate-dependent H2O2 production, which contrasts with the increase of peroxide production by the same particles with NADH as electron donor. Solubilized succinate dehydrogenase generates H2O2 at a much lower rate than the parent submitochondrial particles. It is postulated that ubisemiquinone (and ubiquinol) are chiefly responsible for the succinate-dependent peroxide production by the mitochondrial inner membrane.

Acetone↗

PubMed1975

Polarographic studies on ubiquinone-10 and rhodoquinone bound with chromatophores from Rhodospirillum rubrum.

Redox components bound with chromatophores of Rhodospirillum rubrum, and pure samples of ubiquinone-10 and rhodoquinone were studied polarographically at 24 degrees. In a mixture of ethanol and water (4 : 1, v/v) at pH 7, ubiquinone-10 and rhodoquinone had half-wave potentials (E1/2) OF +43 MV and -63 mV, respectively. For both quinones, values of the electron transfer number (n) were 2 , and plots of E1/2 versus pH formed straight lines with slopes of -30 mV/pH in the neutral pH range; thus, values of the proton transfer number (n-a) were estimated to be 1 for both quinones. When bound with chromatophores, ubiquinone-10 and rhodoquinone had E1/2 values of +50 mV (n=2) and -30 mV (n=2), respectively, at pH 7. Values of (n-a) were estimated to be 1 for ubiquinone-10 and 2 for rhodoquinone. A component (POC-170) thought to be one of the active center bacteriochlorophylls (Liac-890) was characterized; it has E1/2 value of -170 mV at pH 7 and its oxidation-reduction is possibly brought about by dehydrogenation-hydrogenation. Conceivably, the oxidation-reduction sites of ubiquinone-10, rhodoquinone and POC-170 partly, if not all, exist on the surface of chromatophore membrane or project outside the membrane, because of their accessibility to the polarographic electrode.

Bacterial Chromatophores↗

PubMed1978

Sequence of b cytochromes relative to ubiquinone in the electron transport chain of Escherichia coli.

A ubiquinone-deficient mutant, carrying mutations in two genes affecting ubiquinone biosynthesis, has been used, in comparison with a normal strain, to determine the sequence of some of the components of the electron transport chain of Escherichia coli. The amounts of cytochromes reduced during aerobic steady-state conditions were estimated by comparing low-temperature difference spectra of normal or ubiquinone-deficient membranes with either D-lactate or reduced nicotinamide adenine dinucleotide as substrate. From the amounts of cytochromes reduced it was concluded that ubiquinone functions at two sites, one site being between the dehydrogenases and cytochromes and the second site being after cytochromes b562 and b556 but before cytochromes b558, d, and o. The scheme proposed is discussed in relation to the Mitchell protonmotive ubiquinone cycle.

Aerobiosis↗

PubMed1979

Effect of ubiquinone-homologs on the sensitivity of mitochondrial ATPase to energy transfer inhibitors.

Short-chain ubiquinone (UQ-3) abolishes oligomycin sensitivity of ATPase in submitochondrial particles and the effect is reversed by long-chain ubiquinone (UQ-7). Ubiquinone-3 also abolishes DCCD sensitivity of ATPase in submitochondrial particles but the effect is not reversed by long-chain ubiquinones. These data suggest that ubiquinone interferes with energy transfer process by interaction with mitochondrial ATPase.

Adenosine Triphosphatases↗

PubMed1975

The respiratory chain in a ubiquinone-deficient mutant of Saccharomyces cerevisiae.

1. Two allelic mutants of Saccharomyces cerevisiae with a deficiency in the biosynthesis of ubiquinone have been isolated. The properties of one particular mutant strain were investigated. Submitochondrial particles of this strain contain maximally 3% of the amount of ubiquinone in wild-type particles; the amounts of other components of the respiratory chain are essentially normal. 2. The respiratory rates of mutant cells, mitochondria and submitochondrial particles are low with ubiquinone-dependent substrates, but are restored to normal levels by addition of Q-1; the restored respiration is antimycin sensitive. Intact cells and mitochondria show respiratory control both in the absence and presence of Q-1. 3. The NADH:Q-1 oxidoreductase of submitochondrial particles of the mutant followspseudo first-order kinetics in [Q-1]. QH2-1 inhibits competitively with respect to Q-1, the Ki for QH2-1 being equal to the Km for Q-1. 4. Succinate dehydrogenase in both wild-type and mutant submitochondrial particles can be activated by NADH. 5. The turnover number of succinate dehydrogenase in the mutant, measured with phenazine methosulphate as primary electron acceptor, is about one-half that of wild-type particles. The turnover numbers measured with Q-1 as electron acceptor are about the same in the two types of particles. 6. The kinetics of redox changes in cytochrome b, in the presence of antimycin and oxygen, are distinctly different in the mutant and wild-type particles. They indicate that ubiquinone plays an important role in the phenomenon of the increased reducibility of cytochrome b induced by antimycin plus oxygen.

Alleles↗

PubMed1979

The effects of lipid phase transitions on the interaction of mitochondrial NADH--ubiquinone oxidoreductase with ubiquinol--cytochrome c oxidoreductase.

1. The endogenous phosphatidylcholine and phosphatidylethanolamine of Complexes I and III from bovine heart mitochondria may be completely replaced with 1,2-ditetradecanoyl-sn-glycero-3-phosphocholine with at least partial retention of activity. 2. The lipid-replaced enzymes associate in 1:1 molar ratio to give a Complex I--III unit catalysing NADH-cytochrome c oxidoreductase activity. 3. On increasing the concentration of ubiquinone-10 and the synthetic phospholipid, the lipid-replaced Complexes appear to operate independently of each other as in the natural membrane. Thus the lipid-replaced enzymes associate in exactly the same ways as the enzymes containing natural phospholipids. 4. Arrhenius plots of NADH--cytochrome c oxidoreductase activity reconstituted from lipid-replaced Complexes I and III exhibit changes in slope at 24 degrees C. When the concentrations of phospholipid and ubiquinone-10 are increased, the Arrhenius plots show discontinuities at 24 degrees C as well as changes in slope. 5. The kinetics of cytochrome b reduction by NADH were measured in mixtures containing 2 mol of Complex III/mol of Complex I. When the enzymes contained natural phospholipids. the reduction kinetics were biphasic. When the enzymes had been supplemented with further phospholipid and ubiquinone-10 the kinetics were monophasic. When lipid-replaced enzymes were supplemented with 1,2-ditetradecanoyl-sn-glycero-3-phosphocholine and ubiquinone-10, reduction of cytochrome b was monophasic above the phase-transition temperature of the lipid but biphasic below it. 6. These findings are interpreted in terms of the model for the interaction of Complexes in the natural membrane proposed by Heron, Ragan & Trum-power [(1978) Biochem. J. 174, 791--800].

Animals↗

PubMed1975

Ubiquinone-mediated coupling of NADH dehydrogenase to active transport in membrane vesicles from Escherichia coli.

Addition of ubiquinone-1 to E. coli ML 308-225 membrane vesicles dramatically increases coupling between NADH oxidation and active transport such that initial rates and steady-state levels of lactose and amino-acid accumulation are comparable to those observed during D-lactate oxidation. Similar but less dramatic effects are observed with the quinone and succinate or L-lactate. In the presence of NADH and ubiquinone-1, the vesicles also generate a membrane potential (interior negative) that is similar in magnitude to that observed in the presence of D-lactate. Stimulation of NADH-dependent transport by ubiquinone-1 cannot be accounted for by increased rates of oxidation of NADH, and the effect of the quinone on NADH-dependent lactose transport is not observed in vesicles depleted of NADH dehydrogenase activity. Thus, it is apparent that ubiquinone-1 shunts electrons from NADH dehydrogenase [NADH:(acceptor)oxidoreductase; EC 1.6.99.3] to the portion of the respiratory chain containing the energy-coupling site. The findings demonstrate unequivocally that inefficient coupling of NADH oxidation to active transport cannot be due to the presence of inverted vesicles. In addition, they provide further support for specific localization of the energy-coupling site.

Amino Acids↗

PubMed1978

Nonspecific resistance to bacterial infections. Enhancement by ubiquinone-8.

A lipid fraction from Escherichia coli was extracted with apolar solvents and was found to protect mice from a number of experimental bacterial infections. The benzoquinone, ubiquinone-8, was isolated from this extract by high pressure liquid chromatography and identified as such by nuclear magnetic resonance and mass spectrometry. At a dose of 25 mg/kg this substance was found to provide complete protection against otherwise lethal infections with gram-negative and gram-positive bacteria in mice. Treatment was most effective when given intravenously 24 h before infection. In comparative studies, ubiquinone-8 had a clearly higher activity than ubiquinones-4, Q6, and Q10. A highly significant increase in the clearance rate of bacteria from the blood by the spleen and the liver of treated animals, correlated well with the protective effect of ubiquinone-8. The compound stimulated the ability of mouse macrophages to incorporate sheep erythrocytes and significantly increased the number of antibody-producing cells in spleens of mice.

Animals↗

PubMed1978

Dioxygen and temperature dependence of ubiquinone formation in Escherichia coli: studies of cells charged with 2-octaprenyl phenol.

The multiple aromatic auxotroph Escherichia coli K-12 strain AB 2847 (aroB-) was conditioned for efficient ubiquinone-8 formation. Resting cells readily convert 4-hydroxy[U-14C]benzoate into ubiquinone-8 (60 nmol per g wet weight). Under argon this processing stops at the stage of 2-octaprenyl phenol. Only upon admission of air is the pool of 2-octaprenyl phenol converted to ubiquinone-8. This reaction occurs in the cytoplasmic membrane and is significantly inhibited by cytochrome P-450 inhibitors. The rate for 2-octaprenyl phenol conversion is strongly dependent on temperature. The Arrhenius plot shows inflection points at 32 degrees C and 16 degrees C. Enzymes for ubiquinone-8 synthesis are absent from anaerobically grown E. coli. Processing of 4-hydroxy[U-14C]benzoate by these cells starts only when protein synthesis is permitted under aerobic conditions.

Cytochrome P-450 Enzyme System↗

PubMed1975

Role of ubiquinone-10 in electron transport system of chromatophores from Rhodospirillum rubrum.

The role of ubiquinone-10 in the activities for the reduction of free cytochrome c2 and bound cytochrome cc' by succinate was studied with chromatophores from a blue-green mutant (G-9) of Rhodospirillum rubrum. 1. By a single extraction with isooctane, approximately 90% of ubiquinone-10 was easily removed from the chromatophores. In the extracted chromatophores, the activity for succinate-cytochrome c2 reduction decreased to 5-10% of the original activity. This depressed activity was mostly restored by adding ubiquinone-10. The remaining quinone was hardly extractable, even by repeated extractions. With repeatedly extracted chromatophores, the activity for succinate-cytochrome c2 reduction was mostly restored to the same extent as with once-extracted chromatophores, whereas the extent of inhibtion of the activity by antimycin A gradually fell. 2. In isooctane-extracted chromatophores, the activity for the reduction of bound cytochrome cc' by succinate under anaerobic conditions decreased to 35 to 95% of the original level. With chromatophores in which the remaining activity was as low as 40% of the original level, the activity was partially restored by adding ubiquinone-10, but this was not the case with chromatophores in which the remaining activity was higher than approximately 50% of the original level.

Alkanes↗

PubMed1979

A role of ubiquinone in energy conservation in mitochondria.

Short chain ubiquinones (Q-3) uncouple oxidative phosphorylation in rat heart mitochondria, as shown by polarimetric experiments, and abolish P:O ratios in succinate driven oxidative phosphorylaton. The uncoupling is reversed by long chain ubiquinones (Q-7). Furthermore, short chain ubiquinones abolish oligomycin sensitivity of ATPase; the inhibition is restored by Q-7. The extraction of endogenous ubiquinone from mitochondria reversibly lowers oligomycin sensitivity of ATPase.

Animals↗

PubMedDate not supplied

[Effect of phenylalanine and alpha-tocopherol on ubiquinone and ubichromenol metabolism in the liver of E-avitaminotic rats in vitro].

When incubating the liver pulp of vitamin E-deficiency rats with 2-14C-sodium acetate and phenylalanine for an hour the content and radioactivity of ubiquinone and ubichromenol increase as compared to the control level. In this respect phenylalanine in in a dose of 60 and 120 mumol per 1 g of the liver pulp is most effective. Under conditions of these experiments incubation for 3 h causes no noticable changes in the content and metabolism of ubiquinone and ubichromenol in the liver pulp of vitamin E-deficiency rats as compared to the control level. Introduction of different amounts of alpha-tocopherol into the incubation medium results 3 h after an increase in concentration and radioactivity of ubiquinone, the alpha-tocopherol dose of 116 nmol being the most effective. An increase in the concentration and radioactivity of ubichromenol occurs at lower doses of exogenous alpha-tocopherol (58 nmol). All the used doses of alpha-tocopherol cause a decrease in intensity of radio-label incorporation into the unsaponifiable fraction of vitamin E-deficiency rat liver incubated for 3 h. Phenylalanine also results in a decrease of these values with the system incubation for an hour and produces no changes in them in the 3 h incubation. The results of the experiments give grounds to suppose the presence of interrelation between alpha-tocopherol and biosynthesis of ubiquinone and ubichromenol in the rat liver.

Animals↗

PubMed1976

[Effect of training for increased physical loads on the concentration and biosynthesis of ubiquinones in rat skeletal muscle].

Rats were subjected to a strenuous program of treadmill running for 2.5--3 months. Ubiquinone content was determined in the skeletal muscles and the muscle mitochondria; at the same time incorporation of labeled acetate-1-14C precursor into ubiquinone and sterols by thin muscle slices was studied. Ubiquinone and mitochondrial protein content increased in the muscles of trained rats. Incorporation of 14C into ubiquinone of trained rats increased; as to sterols, their incorporation remained unchanged.

Acetates↗

PubMed1975

Thermodynamic and EPR characterization of iron-sulfur centers in the NADH-ubiquinone segment of the mitochondrial respiratory chain in pigeon heart.

Several iron-sulfur centers in the NADH-ubiquinone segment of the respiratory chain in pigeon heart mitochondria and in submitochondrial particles were analyzed by the combined application of cryogenic EPR (between 30 and 4.2 degrees K) and potentiometric titration. Center N-1 (iron-sulfur centers associated with NADH dehydrogenase are designated with the prefix "N") resolves into two single electron titratins with EM7.2 values of minus 380 plus or minus 20 mV and minus 240 plus or minus 20 mV (Centers N-1a and N-1b, respectively). Center N-1a exhibits an EPR spectrum of nearly axial symmetry with g parellel = 2.03, g = 1.94, while that of Center N-1b shows more apparent rhombic symmetry with gz = 2.03, gy = 1.94 and gx = 1.91. Center N-2 also reveals EPR signals of axial symmetry at g parallel = 2.05 and g = 1.93 and its principal signal overlaps with those of Centers N-1a and N-1b. Center N-2 can be easily resolved from N-1a and N-1b because of its high EM7.2 value (minus 20 plus or minus 20 mV). Resolution of Centers N-3 and N-4 was achieved potentiometrically in submitochondrial particles. The component with EM7.2 = minus 240 plus or minus 20 mV is defined as Center N-3 (gz = 2.10, (gz = 2.10, (gy = 1.93?), GX = 1.87); the minus 405 plus or minus 20 mV component as Center N-4 (gz = 2.11, (gy = 1.93?), gx = 1.88). At temperatures close to 4.2 degrees K, EPR signals at g = 2.11, 2.06, 2.03, 1.93, 1.90 and 1.88 titrate with EM7.2 = minus 260 plus or minus 20 mV. The multiplicity of peaks suggests the presence of at least two different iron-sulfur centers having similar EM7.2 values (minus 260 plus or minus 20 mV); HENCE, tentatively assigned as N-5 and N-6. Consistent with the individual EM7.2 values obtained, addition of succinate results in the partial reduction of Center N-2, but does not reduce any other centers in the NADH-ubiquinone segment of the respiratory chain. Centers N-2, N-1b, N-3, N-5 and N-6 become almost completely reduced in the presence of NADH, while Centers N-1a and N-4 are only slightly reduced in pigeon heart submitochondrial particles. In pigeon heart mitochondria, the EM7.2 of Center N-4 lies much closer to that of Center N-3, so that resolution of the Center N-3 and N-4 spectra is not feasible in mitochondrial preparations. EM7.2 values and EPR lineshapes for the other iron-sulfur centers of the NADH-ubiquinone segment in the respiratory chain of intact mitochondria are similar to those obtained in submitochondrial particle preparations. Thus, it can be concluded that, in intact pigeon heart mitochondria, at least five iron-sulfur centers show EM7.2 values around minus 250 mV; Center N-2 exhibits a high EM7.2 (minus 20 plus or minus 20 mV), while Center N-1a shows a very low EM7.2 (minus 380 plus or minus 20 mV).

Animals↗

PubMed1977

Secondary electron transfer in reaction centers of Rhodopseudomonas sphaeroides. Out-of-phase periodicity of two for the formation of ubisemiquinone and fully reduced ubiquinone.

Electron transfer between purified reaction centers from Rhodopseudomonas sphaeroides and exogenous ubiquinone has been studied in the presence of electron donors by measurements of light-induced absorbance changes following a sequence of short actinic light flashes. Each odd flash promotes the formation of a molecule of ubisemiquinone; after each even flash the semiquinone disappears and a molecule of the fully reduced quinone appears. We interpret these results by means of a model where a specialized molecule of ubiquinone is reduced by the primary electron acceptor in a one-electron transfer reaction after each flash, and is reoxidized by a molecule of the ubiquinone pool in a two-electron transfer reaction every two flashes.

Darkness↗

PubMed1979

The involvement of iron and ubiquinone in electron transfer reactions mediated by reaction centers from photosynthetic bacteria.

Reaction centers from Rhodopseudomonas sphaeroides strain R-26 were prepared with varying Fe and ubiquinone (Q) contents. The photooxidation of P-870 to P-870+ was found to occur with the same quantum yield in Fe-depleted reaction centers as in control samples. The kinetics of electron transfer from the initial electron acceptor (I) to Q also were unchanged upon Fe removal. We conclude that Fe has no measurable role in the primary photochemical reaction. The extent of secondary reaction from the first quinone acceptor (QA) to the second quinone acceptor (QB) was monitored by the decay kinetics of P-870+ after excitation of reaction centers with single flashes in the absence of electron donors, and by the amount of P-870 photooxidation that occurred on the second flash in the presence of electron donors. In reaction centers with nearly one iron and between 1 and 2 ubiquinones per reaction center, the amount of secondary electron transfer is proportional to the ubiquinone content above one per reaction center. In reaction centers treated with LiClO4 and o-phenanthroline to remove Fe, the amount of secondary reaction is decreased and is proportional to Fe content. Fe seems to be required for the secondary reaction. In reaction centers depleted of Fe by treatment with SDS and EDTA, the correlation between Fe content and secondary activity is not as good as that found using LiClO4. This is probably due in part to a loss of primary photochemical activity in samples treated with SDS; but the correlation is still not perfect after correction for this effect. The nature of the back reaction between P-870+ and Q-B was investigated using stopped flow techniques. Reaction centers in the P-870+ Q-B state decay with a 1-s half-time in both the presence and absence of o-phenanthroline, an inhibitor of electron transfer between Q-B and QB. This indicates that the back reaction between P-870+ and Q-A is direct, rather than proceeding via thermal repopulation of Q-A. The P-870+ Q-B state is calculated to lie at least 100 mV in free energy below the P-870+ Q-A state.

Bacteriochlorophylls↗

PubMed1977

Interactions of tocopherols and ubiquinones with monolayers of phospholipids.

1. The penetration of alpha-tocopherol and seven of its derivatives, and five compounds in the ubiquinone series, having differing chain lengths, into monolayers at the air/water interface of 11 different synthetic phospholipids and cholesterol was investigated; the properties of mixed monolayers of the tocopherols and of ubiquinones with phospholipids were also studied. 2. Penetration of alpha-tocopherol into diarachidonylglycerylphosphorycholine was approximately constant for molar ratios of tocopherol/phospholipid ranging from 0.4:1.0 to 2.0:1.0. 3. Tocopherols with shorter or longer side chains than alpha-tocopherol had a lesser ability to penetrate monolayers of phospholipid molecules with 16 or more carbon atoms in their acyl chains. 4. All the tocopherols penetrated more readily as unsaturation in the phospholipids was increased, and their penetration into mixed monolayers of phospholipids was greatly facilitated by the presence of relatively small quantities of unsaturated phospholipid molecules. 5. There was relatively little interaction between the tocopherols and cholesterol, or between the ubiquinones and phospholipids. 6. The possible significance of the observed interactions between alpha-tocopherol and polyunsaturated phospholipids is discussed in relation to the biochemical actions of alpha-tocopherol in vivo. 7. It is suggested that fluidity of the lipid bilayer in membranes containing polyunsaturated phospholipids may allow alpha-tocopherol to interact in a dynamic manner with a number of phospholipid molecules.

Membranes↗