Studies with ubiquinone-depleted submitochondrial particles. Effects of extraction and reincorporation of ubiquinone on the kinetics of succinate dehydrogenase

Pro- and anti-oxidant activities of the mitochondrial respiratory chain: factors influencing NAD(P)H-induced lipid peroxidation

This paper is a study of factors influencing the rate of lipid peroxidation in beef heart submitochondrial particles induced by NAD(P)H via the NADH-ubiquinone oxidoreductase (Complex I) of the respiratory chain. In accordance with earlier observations, both NADH and NADPH initiated lipid peroxidation in the presence of ADP-Fe3+. The rate of the reaction, measured as oxygen consumption and formation of thiobarbituric acid reactive substances, was biphasic as a function of NADH concentration, reaching a maximum at low NADH concentrations and then declining. In contrast, the NADPH-initiated lipid peroxidation showed a monophasic concentration profile of hyperbolic character. Rotenone did not eliminate the biphasicity of the NADH-induced reaction, indicating that this was not due to an antioxidant effect of reduced ubiquinone at high NADH concentrations. This conclusion was further supported by the demonstration that extraction of ubiquinone from the particles did not relieve the inhibition of lipid peroxidation by high NADH concentrations. However rhein, another inhibitor of Complex I, eliminated the biphasicity, and even caused a substantial stimulation of the NADH-induced lipid peroxidation in the particles upon extraction of ubiquinone by pentane. No similar effect occurred in the case of NADPH-induced lipid peroxidation. Furthermore, rhein facilitated both NADH- and NADPH-induced lipid peroxidation even in the absence of added ADP-Fe3+, in a fashion similar to that earlier reported with succinate in the presence of theonyltrifluoroacetone. Based on these findings and measurements of the redox states of ubiquinone and cytochromes in the presence of KCN and NADH or NADPH, it is concluded that Complex I may distinguish between electron input from NADH and NADPH by differences in the site(s) of substrate binding and in the pathways and rates of NADH and NADPH oxidation.

Lipid peroxidation and changes in the ubiquinone content and the respiratory chain enzymes of submitochondrial particles

The relationship between, lipid peroxidation induced by ascorbate and adenosine ADP/Fe3+, and its effect on the respiratory chain activities of beef heart submitochondrial particles has been investigated. Lipid peroxidation, measured as thiobarbituric acid reactive substance formation, resulted in an inhibition of the NADH and succinate oxidase activities. Examination of several partial reactions of the respiratory chain revealed inactivation primarily of those involving endogenous ubiquinone, i.e., NADH- and succinate-ubiquinone1 and cytochrome c reductases. Ubiquinol-cytochrome c reductase, measured with reduced ubiquinone2 as electron donor, was unaffected. The amount of NADH- or succinate-reducible cytochrome b in the presence of cyanide was strongly decreased, but could be recovered by the addition of antimycin. There occurred a substantial decrease of the ubiquinone content in the course of lipid peroxidation, with a linear relationship between this decrease and the NADH and succinate oxidase activities. The results are consistent with the conclusion that the ubiquinone pool undergoes an oxidative modification during lipid peroxidation, to a form that can no longer function as a component of the respiratory chain. Lipid peroxidation also led to a partial inhibition of the succinate dehydrogenase and cytochrome c oxidase activities and a minor decrease of the cytochrome c and cytochrome a contents. Reduction of endogenous ubiquinone prevented lipid peroxidation as well as the concomitant modification of ubiquinone and inactivation of the respiratory chain. These observations suggest that the destruction of ubiquinone through lipid peroxidation is the primary cause of inactivation of the respiratory chain, and emphasize the antioxidant role of ubiquinol in preventing these effects. The possible implications of these findings for regulation of the cellular turnover of ubiquinone by the prevailing oxidative stress are discussed.

Lovastatin decreases coenzyme Q levels in rats

Lovastatin is used for the treatment of hypercholesterolemia. It functions by inhibiting the enzyme, 3-hydroxy-3-methylglutaryl-coenzyme A reductase (EC 1.1.1.34), that is required for the conversion of 3-hydroxy-3-methylglutaryl-coenzyme A to mevalonic acid. Since biosynthesis of both cholesterol and coenzyme Q (CoQ) requires mevalonic acid as a precursor, it was considered that lovastatin therapy would also result in a lowering of cellular CoQ levels. This study was conducted to determine whether lovastatin treatment does decrease CoQ levels and whether such decreases can be prevented by CoQ supplementation. Forty-five adult male Holtzman rats were randomly assigned to one of three treatment groups. Controls were fed ground laboratory rat chow ad libitum. The other two groups were fed ground laboratory rat chow containing 400 mg of lovastatin per kg of diet ad libitum. One of the lovastatin-fed groups received CoQ10 (15 mg per kg of body weight) daily via stomach intubation. After 4 weeks, samples of heart, liver, and blood were analyzed for CoQ concentrations. Results indicated that CoQ concentrations in all tissues analyzed were decreased in lovastatin-treated rats. Lovastatin-treated animals that were supplemented with CoQ10 had blood, heart, and liver CoQ10 concentrations that approximated or exceeded those of control animals. It is concluded that lovastatin does indeed lower tissue concentrations of CoQ and that a return to normal can be achieved by supplementation with CoQ.

The participation of coenzyme Q in free radical production and antioxidation

Published experimental data pertaining to the participation of coenzyme Q as a site of free radical formation in the mitochondrial electron transfer chain and the conditions required for free radical production have been reviewed critically. The evidence suggests that a component from each of the mitochondrial NADH-coenzyme Q, succinate-coenzyme Q, and coenzyme QH2-cytochrome c reductases (complexes I, II, and III), most likely a nonheme iron-sulfur protein of each complex, is involved in free radical formation. Although the semiquinone form of coenzyme Q may be formed during electron transport, its unpaired electron most likely serves to aid in the dismutation of superoxide radicals instead of participating in free radical formation. Results of studies with electron transfer chain inhibitors make the conclusion dubious that coenzyme Q is a major free radical generator under normal physiological conditions but may be involved in superoxide radical formation during ischemia and subsequent reperfusion. Experiments at various levels of organization including subcellular systems, intact animals, and human subjects in the clinical setting, support the view that coenzyme Q, mainly in its reduced state, may act as an antioxidant protecting a number of cellular membranes from free radical damage.

Inhibition by coenzyme Q of ethanol- and carbon tetrachloride-stimulated lipid peroxidation in vivo and catalyzed by microsomal and mitochondrial systems

The ability of coenzyme Q to inhibit lipid peroxidation in intact animals as well as in mitochondrial, submitochondrial, and microsomal systems has been tested. Rats fed coenzyme Q prior to being treated with carbon tetrachloride or while being treated with ethanol excrete less thiobarbituric acid-reacting material in the urine than such rats not fed coenzyme Q. Liver homogenates, mitochondria, and microsomes isolated from rats treated with carbon tetrachloride and ethanol catalyze lipid peroxidation at rates which exceed those from animals also fed coenzyme Q. The rate of lipid peroxidation catalyzed by submitochondrial particles isolated from hearts of young, old, and endurance trained elderly rats was inversely proportional to the coenzyme Q content of the submitochondrial preparation in assays in which succinate was employed to reduce the endogenous coenzyme Q. Reduced, but not oxidized, coenzyme Q inhibited lipid peroxidation catalyzed by rat liver microsomal preparations. These results provide additional evidence in support of an antioxidant role for coenzyme Q.

Differential investigation of the capacity of succinate oxidation in human skeletal muscle

Procedures are described for the estimation of the succinate:ubiquinone oxidoreductase and succinate:phenazine methosulfate oxidoreductase activities in post-nuclear supernatants of human skeletal muscle homogenates using 2,6-dichlorophenol indophenol as the terminal electron acceptor. The influence of ionic strength and of sucrose upon these assays and upon the succinate:cytochrome c oxidoreductase activity has been investigated. Sucrose markedly interferes with the activation of the succinate dehydrogenase complex. Succinate:cytochrome c oxidoreductase activity and succinate:phenazine methosulfate oxidoreductase activity are inhibited by increasing concentrations of ions and of sucrose. Our results lead us to propose the existence of a single acceptor site for phenazine methosulfate at the succinate dehydrogenase complex, not involved in the physiological electron flux across ubiquinone. Estimation of the enzymatic activities mentioned above allows differential investigation of the functional integrity of a large part of the respiratory chain in patients suspected of suffering from a neuromuscular disorder.

Tissue coenzyme Q (ubiquinone) and protein concentrations over the life span of the laboratory rat

The coenzyme Q (ubiquinone) concentrations of a number of tissues have been determined over the life span of the male laboratory rat. Coenzyme Q increased between 2 and 18 months and decreased significantly at 25 months in the heart and kidney, and the gastrocnemius, oblique and deep aspect (red) vastus lateralis muscles. The coenzyme Q concentration of liver increased over the life span, while it remained relatively constant in brain, lung, and the superficial aspect (white) of the vastus lateralis muscle. Data are also included for organ weights and protein contents of tissues over the life span. The various roles of coenzyme Q in cellular electron transfer and its regulation, energy conservation in oxidative phosphorylation, and its clinical efficacy in diseases of energy metabolism are discussed. It is hypothesized that coenzyme Q serves as a free radical quencher in the mitochondrion, a major site of free radical formation, in addition to its other roles in cellular energy metabolism, and that its cellular diminution may contribute to the loss of cellular function accompanying ageing.

Studies on the succinate dehydrogenating system. Isolation and properties of the mitochondrial succinate-ubiquinone reductase

A simple procedure for preparation of highly purified soluble succinate-ubiquinone reductase from bovine heart mitochondrial particles is described. The enzyme exhibits four major bands on sodium dodecyl sulfate gel electrophoresis and contains (nmol per mg protein): covalently bound flavin, 6; non-heme iron, 53; acid-labile sulfur, 50; cytochrome b-560 heme, 1.2. The enzyme catalyzes thenoyltrifluoroacetone, or carboxin-sensitive (pure non-competitive with Q2) reduction of Q2 by succinate with a turnover number close to that in parent submitochondrial particles. The succinate reduced enzyme exhibits ferredoxin-type iron-sulfur center EPR-signal (g = 1.94 species) and a semiquinone signal (g = 2.00). An oxidized preparation shows a symmetric signal centered around g = 2.01. An unusual dissociation of the enzyme in the absence of a detergent is described. When added to the assay mixture from a concentrated protein-detergent solution, the enzyme does not reduce Q2 being highly reactive towards ferricyanide ('low Km ferricyanide reactive site'; Vinogradov, A.D., Gavrikova, E.V. and Goloveshkina, V.G. (1975) Biochem. Biophys. Res. Commun. 65, 1264-1269). The ubiquinone reductase, not the ferricyanide reductase was observed when the enzyme was added to the assay mixture from the diluted protein-detergent solutions. Thus the dissociation of succinate dehydrogenase from the complex occurs in the absence of a detergent dependent on the concentration of the protein-detergent complex in the stock preparation where the samples for the assay are taken from. An active antimycin-sensitive succinate-cytochrome c reductase was reconstituted by admixing of the soluble succinate-ubiquinone reductase and the cytochrome b-c1 complex, i.e., from the complexes which both contain the ubiquinone reactivity conferring protein (QPs). Cytochrome c reductase was also reconstituted from the succinate-ubiquinone reductase and succinate-cytochrome c reductase containing inactivated succinate dehydrogenase. The reconstitution experiments suggest that there exists a specific protein-protein (or lipid) interaction between QPs and a certain component(s) of the b-c1 complex.

Elevation of tissue coenzyme Q (ubiquinone) and cytochrome c concentrations by endurance exercise in the rat

Six months of enforced and voluntary endurance training of young female Wistar rats resulted in significant decreases of body weight and gastrocnemius muscle wet weight and protein content, and increases in heart weight and protein content, and liver protein content. The coenzyme Q and cytochrome c concentrations of cardiac, gastrocnemius, and deep red region of the vastus lateralis muscles were increased, while small or nonsignificant trends toward increases in cytochrome c and coenzyme Q were seen in kidney, brain, lung, liver, internal + external oblique muscles, and the superficial white region of the vastus lateralis muscle. These results are discussed with regard to several roles for coenzyme Q in cellular function.

Alterations of oxidative phosphorylation reactions in mitochondria isolated from hypothyroid rat liver

Several parameters of oxidative phosphorylation reaction were studied in vitro in isolated liver mitochondria from hypothyroid rats. When succinate was employed as a respiratory substrate for mitochondria incubated in a mannitol/sucrose/phosphate buffer, and measurements were performed during initial additions of ADP, the magnitude of state 3 and state 4 respiration was not different between mitochondria from the hypothyroid and those from the control rats. During the course of repetitive additions of ADP and consequently of sequential transitions from state 4 to state 3 and back to state 4, mitochondria from hypothyroid animals showed a gradual decline in the rate of both state 3 and state 4 respiration whereas those from normal animals did not. The total succinate dehydrogenase activity was not different between the two types of mitochondria, and the decline in state 3 and state 4 respiration was not accompanied by any change in the apparent Km for ADP or in the corrected ADP/O ratio [Biochem. Biophys. Res. Commun. (1973) 53, 988]. The amount of oxygen consumed during the state-4----3----4 transition was lower in the hypothyroid than in the control mitochondria. These alterations were reversed if the hypothyroid animals were injected with thyroxine intraperitoneally (2 micrograms/100 g body weight) for 3 weeks before isolation of mitochondria. These results indicate that the fall of respiratory activity in hypothyroidism may result from the decrease not only of respiratory activities of state 3 and state 4, but also of the energy spent in the process of the state-4----3----4 transition, while the coupling efficiency per se remains normal. These properties become manifest when mitochondria respond to pulses of ADP load, a situation likely to occur in situ.

Interaction of the membrane-bound succinate dehydrogenase with substrate and competitive inhibitors

The protective effect of dicarboxylates on the active-site-directed inhibition of the membrane-bound succinate dehydrogenase by N-ethylmaleimide, steady-state kinetics methods for Ki and Ks determinations, and equilibrium studies were employed to quantitate the relative affinities of succinate, fumarate, malonate and oxaloacetate to the reduced and oxidized species of the enzyme. A more than 10-fold difference in the relative affinities of the reduced and oxidized succinate dehydrogenase to succinate, fumarate and oxaloacetate is found, whereas the reactivity of the active-site sulphydryl group does not depend on the redox state of the enzyme. The redox-state-dependent changes in the affinity of the membrane-bound succinate dehydrogenase to oxaloacetate can be quantitatively accounted for by a 10-fold increase in the rate of dissociation of the enzyme-inhibitor complex which occurs upon reduction of the enzyme. The data obtained give no support for either the existence of a sulphydryl group other than the active-site one important for the catalysis or for the presence of a separate dicarboxylate-specific regulatory site in the succinate dehydrogenase molecule.

Tetrazolium method for studying the catalytic properties of oxidoreductases in cellular organelles immobilized on glass surfaces

A new quantitative method allowing the measurement of the activity of oxidoreductases, as well as the study of their catalytic properties, is proposed. The method is based on photometering a smear of cellular organelles in the course of incubation in medium containing the reductase substrate and an artificial electron acceptor, tetrazolium salt. Catalytic properties of succinate:p-nitrotetrazolium violet reductase, as revealed on the smears, are shown to be identical to those of the reductase in mitochondrial suspension. Under similar conditions the maximal oxidation rate of succinate with p-nitrotetrazolium violet is the same as that in the presence of an acceptor of another type, Wurster's blue. The method allows the study of a number of reductases.

The reconstitution of oxidative phosphorylation in mitochondria isolated from a ubiquinone-deficient mutant of Saccharomyces cerevisiae

Mitochondria, isolated from the ubiquinone-deficient nuclear mutant of Saccharomyces cerevisiae E3-24, are practically unable to oxidize exogenous substrates. Respiratory activity, coupled to ATP synthesis, can, however, be reconstituted by the simple addition of ethanolic solutions of ubiquinones. A minimal length of the isoprenoid side chain (greater than or equal to 3) was required for the restoration. Saturation of the reconstitution required a large amount of exogeneous ubiquinone, in excess over the normal content present in the mitochondria of the wild type strain. A similar pattern of reconstituted activities could be also obtained using sonicated inverted particles. Mitochondria and sonicated particles are also able to carry out a dye-mediated electron flow coupled to ATP synthesis in the absence of added ubiquinone, using ascorbate or succinate as electron donor. This demonstrates that the energy conserving mechanism at the third coupling site of the respiratory chain is fully independent of the presence of the large mobile pool of ubiquinone in the membrane.

On the site of action of the inhibition of the mitochondrial respiratory chain by lipoxygenase

Treatment of beef-heart submitochondrial particles with reticulocyte lipoxygenases gives rise to a strong irreversible inhibition of the NADH and succinate oxidase activities. This is not accompanied by any loss of the Fe-S clusters of the respiratory chain as determined by EPR spectroscopy. The inhibitory blockage is located between both the NADH and succinate dehydrogenases and Q-10. The inhibitory action of treatment with lipoxygenase also takes place in the absence of Q-10. The Fe-S clusters of the mitochondrial outer membrane are destroyed by lipoxygenase treatment, without any effect on the rotenone-insensitive NADH: cytochrome c oxidoreductase activity. It is concluded that these clusters are not involved in this enzyme.

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

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.

Immunological studies on beef-heart ubiquinol--cytochrome c reductase (complex III)

Antibodies against isolated beef-heart ubiquinol--cytochrome c reductase (complex III) have been characterized. Antibodies to complex III react strongly with isolated beef heart complex III and intact beef heart mitochondria, as shown by immunodiffusion and rocket electrophoresis experiments. The complex III content of intact mitochondria can be quantitated with rocket electrophoresis using isolated complex III as a standard. Antibodies to complex III also react with beef liver mitochondria and with both heart and liver mitochondria from rats. The latter are very weak antigens compared to beef heart material. Antibodies to complex III do not react with respiratory chain complexes I and IV, or F1-ATPase from beef heart mitochondria, but gives a slight, but variable, reaction with complex II and the membrane fraction isolated from complex V (oligomycin-sensitive ATPase). Antigenic sites are located on at least five of the seven peptides of complex III. These peptides are presumably lacking in respiratory chain complexes which do not react with antibodies to complex III, and are assumed to be uniquely located in complex III. Antiserum against complex III inhibitis duroquinol--cytochrome c reductase activity in isolated complex III and in complex III incorporated into phospholipid vesicles. Oxidation of NADH and succinate is not affected in submitochondrial particles treated with 6-times more antibody than required for complete inhibition of enzyme activity in free complex III or in complex III-phospholipid vesicles.

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.

The mitochondrial generation of hydrogen peroxide. General properties and effect of hyperbaric oxygen

1. Pigeon heart mitochondria produce H(2)O(2) at a maximal rate of about 20nmol/min per mg of protein. 2. Succinate-glutamate and malate-glutamate are substrates which are able to support maximal H(2)O(2) production rates. With malate-glutamate, H(2)O(2) formation is sensitive to rotenone. Endogenous substrate, octanoate, stearoyl-CoA and palmitoyl-carnitine are by far less efficient substrates. 3. Antimycin A exerts a very pronounced effect in enhancing H(2)O(2) production in pigeon heart mitochondria; 0.26nmol of antimycin A/mg of protein and the addition of an uncoupler are required for maximal H(2)O(2) formation. 4. In the presence of endogenous substrate and of antimycin A, ATP decreases and uncoupler restores the rates of H(2)O(2) formation. 5. Reincorporation of ubiquinone-10 and ubiquinone-3 to ubiquinone-depleted pigeon heart mitochondria gives a system in which H(2)O(2) production is linearly related to the incorporated ubiquinone. 6. The generation of H(2)O(2) by pigeon heart mitochondria in the presence of succinate-glutamate and in metabolic state 4 has an optimum pH value of 7.5. In states 1 and 3u, and in the presence of antimycin A and uncoupler, the optimum pH value is shifted towards more alkaline values. 7. With increase of the partial pressure of O(2) to the hyperbaric region the formation of H(2)O(2) is markedly increased in pigeon heart mitochondria and in rat liver mitochondria. With rat liver mitochondria and succinate as substrate in state 4, an increase in the pO(2) up to 1.97MPa (19.5atm) increases H(2)O(2) formation 10-15-fold. Similar pO(2) profiles were observed when rat liver mitochondria were supplemented either with antimycin A or with antimycin A and uncoupler. No saturation of the system with O(2) was observed up to 1.97MPa (19.5atm). By increasing the pO(2) to 1.97MPa (19.5atm), H(2)O(2) formation in pigeon heart mitochondria with succinate as substrate increased fourfold in metabolic state 4, with antimycin A added the increase was threefold and with antimycin A and uncoupler it was 2.5-fold. In the last two saturation of the system with oxygen was observed, with an apparent K(m) of about 71kPa (0.7-0.8atm) and a V(max.) of 12 and 20nmol of H(2)O(2)/min per mg of protein. 8. It is postulated that in addition to the well-known flavin reaction, formation of H(2)O(2) may be due to interaction with an energy-dependent component of the respiratory chain at the cytochrome b level.