Interaction between succinate dehydrogenase and ubiquinone-binding protein from succinate-ubiquinone reductase

The Good, the Bad, and the Ugly of ROS: New Insights on Aging and Aging-Related Diseases from Eukaryotic and Prokaryotic Model Organisms

Aging is associated with the accumulation of cellular damage over the course of a lifetime. This process is promoted in large part by reactive oxygen species (ROS) generated via cellular metabolic and respiratory pathways. Pharmacological, nonpharmacological, and genetic interventions have been used to target cellular and mitochondrial networks in an effort to decipher aging and age-related disorders. While ROS historically have been viewed as a detrimental byproduct of normal metabolism and associated with several pathologies, recent research has revealed a more complex and beneficial role of ROS in regulating metabolism, development, and lifespan. In this review, we summarize the recent advances in ROS research, focusing on both the beneficial and harmful roles of ROS, many of which are conserved across species from bacteria to humans, in various aspects of cellular physiology. These studies provide a new context for our understanding of the parts ROS play in health and disease. Moreover, we highlight the utility of bacterial models to elucidate the molecular pathways by which ROS mediate aging and aging-related diseases.

(Un)suitability of the use of pH buffers in biological, biochemical and environmental studies and their interaction with metal ions – a review

The present work reviews, discusses and update the metal complexation characteristics of thirty one buffers commercially available. Additionally, their impact on the biological systems is also presented and discussed.

Inhibitors of succinate: quinone reductase/Complex II regulate production of mitochondrial reactive oxygen species and protect normal cells from ischemic damage but induce specific cancer cell death

Succinate:quinone reductase (SQR) of Complex II occupies a unique central point in the mitochondrial respiratory system as a major source of electrons driving reactive oxygen species (ROS) production. It is an ideal pharmaceutical target for modulating ROS levels in normal cells to prevent oxidative stress-induced damage or alternatively,increase ROS in cancer cells, inducing cell death.The value of drugs like diazoxide to prevent ROS production,protecting normal cells, whereas vitamin E analogues promote ROS in cancer cells to kill them is highlighted. As pharmaceuticals these agents may prevent degenerative disease and their modes of action are presently being fully explored. The evidence that SDH/Complex II is tightly coupled to the NADH/NAD+ ratio in all cells,impacted by the available supplies of Krebs cycle intermediates as essential NAD-linked substrates, and the NAD+-dependent regulation of SDH/Complex II are reviewed, as are links to the NAD+-dependent dehydrogenases, Complex I and the E3 dihiydrolipoamide dehydrogenase to produce ROS. This review collates and discusses diverse sources of information relating to ROS production in different biological systems, focussing on evidence for SQR as the main source of ROS production in mitochondria, particularly its relevance to protection from oxidative stress and to the mitochondrial-targeted anti cancer drugs (mitocans) as novel cancer therapies [corrected].

Genome-wide screen identifies Escherichia coli TCA-cycle-related mutants with extended chronological lifespan dependent on acetate metabolism and the hypoxia-inducible transcription factor ArcA

Single-gene mutants with extended lifespan have been described in several model organisms. We performed a genome-wide screen for long-lived mutants in Escherichia coli, which revealed strains lacking tricarboxylic acid (TCA)-cycle-related genes that exhibit longer stationary-phase survival and increased resistance to heat stress compared to wild-type. Extended lifespan in the sdhA mutant, lacking subunit A of succinate dehydrogenase, is associated with the reduced production of superoxide and increased stress resistance. On the other hand, the longer lifespan of the lipoic acid synthase mutant (lipA) is associated with reduced oxygen consumption and requires the acetate-producing enzyme pyruvate oxidase, as well as acetyl-CoA synthetase, the enzyme that converts extracellular acetate to acetyl-CoA. The hypoxia-inducible transcription factor ArcA, acting independently of acetate metabolism, is also required for maximum lifespan extension in the lipA and lpdA mutants, indicating that these mutations promote entry into a mode normally associated with a low-oxygen environment. Because analogous changes from respiration to fermentation have been observed in long-lived Saccharomyces cerevisiae and Caenorhabditis elegans strains, such metabolic alterations may represent an evolutionarily conserved strategy to extend lifespan.

Identification of quinone-binding and heme-ligating residues of the smallest membrane-anchoring subunit (QPs3) of bovine heart mitochondrial succinate:ubiquinone reductase

The smallest membrane-anchoring subunit (QPs3) of bovine heart succinate:ubiquinone reductase was overexpressed in Escherichia coli JM109 as a glutathione S-transferase fusion protein using the expression vector pGEX2T/QPs3. The yield of soluble active recombinant glutathione S-transferase-QPs3 fusion protein was isopropyl-1-thio-beta-D-galactopyranoside concentration-, induction growth time-, temperature-, and medium-dependent. Maximum yield of soluble recombinant fusion protein was obtained from cells harvested 3.5 h post-isopropyl-1-thio-beta-D-galactopyranoside (0.4 mM)-induction growth at 25 degrees C in 2.0% tryptone, 0.5% yeast extract, 10 mM NaCl, 2.5 mM KCl, 10 mM MgCl2, 20 mM glucose (SOC medium) containing 440 mM sorbitol and 2.5 mM betaine. QPs3 was released from the fusion protein by proteolytic cleavage with thrombin. Isolated recombinant QPs3 shows one protein band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis that corresponds to subunit V of mitochondrial succinate:ubiquinone reductase. Although purified recombinant QPs3 is dispersed in 0.01% dodecylmaltoside, it is in a highly aggregated form, with an apparent molecular mass of more than 1 million. The recombinant QPs3 binds ubiquinone, causing a spectral blue shift. Upon titration of the recombinant protein with ubiquinone, a saturation behavior is observed, suggesting that the binding is specific and that recombinant QPs3 may be in the functionally active state. Two amino acid residues, serine 33 and tyrosine 37, in the putative ubiquinone binding domain of QPs3 are involved in ubiquinone binding because the S33A- or Y37A-substituted recombinant QPs3s do not cause the spectral blue shift of ubiquinone. Although recombinant QPs3 contains little cytochrome b560 heme, the spectral characteristics of cytochrome b560 are reconstituted upon addition of hemin chloride. Reconstituted cytochrome b560 in recombinant QPs3 shows a EPR signal at g = 2.92. Histidine residues at positions 46 and 60 are responsible for heme ligation because the H46N- or H60N-substituted QPs3 fail to restore cytochrome b560 upon addition of hemin chloride.

Involvement of a histidine residue in the interaction between membrane-anchoring protein (QPs) and succinate dehydrogenase in mitochondrial succinate-ubiquinone reductase

The involvement of a histidine residue of the membrane-anchoring protein (QPs) fraction in reconstitution of succinate dehydrogenase to form succinate-ubiquinone reductase is studied by using a histidine-modifying reagent, diethylpyrocarbonate (DEPC). A maximum inactivation of 80% of reconstitutive activity is obtained when QPs is treated with 1 mM DEPC at 0 degrees C for 30 min in 50 mM Tris-HCl (pH 7.0). DEPC also inactivates about 85% of intact succinate-ubiquinone reductase. The inactivation of succinate-ubiquinone reductase by DEPC is a result of the modification of essential histidine residues of succinate dehydrogenase. The inactivation is not a result of the modification of the histidine residue in QPs which is essential for interaction with succinate dehydrogenase because the QPs dissociated from the inactivated succinate-ubiquinone reductase is active in reconstitution with active succinate-dehydrogenase. Apparently, the essential histidine in QPs is shielded by succinate dehydrogenase and thus inaccessible to DEPC modification in succinate-ubiquinone reductase. The involvement of a histidine residue of QPs in interaction with succinate dehydrogenase is further evident by the presence of 553 nm shoulder on the alpha-absorption peak of reduced cytochrome b-560 (a characteristic of physical association of QPs with succinate dehydrogenase) in the DEPC-inactivated succinate-ubiquinone reductase. This shoulder disappears from a mixture of succinate dehydrogenase and DEPC-treated QPs when reduced with dithionite. About one histidine residue per molecule of QPs is modified in the DEPC-treated sample, suggesting that only one histidine residue is essential for interaction with succinate dehydrogenase. This essential histidine group is located in the smaller subunit (Mr 13,000) of QPs.

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.

Purification and properties of succinate-ubiquinone oxidoreductase complex from Paracoccus denitrificans

Highly active succinate-ubiquinone reductase has been purified from cytoplasmic membranes of aerobically grown Paracoccus denitrificans. The purified enzyme has a specific activity of 100 units per mg protein, and a turnover number of 305 s-1. Succinate-ubiquinone reductase activity of the purified enzyme is inhibited by 3'-methylcarboxin and thenoyltrifluoroacetone. Four subunits, with apparent molecular masses of 64.9, 28.9, 13.4 and 12.5 kDa, were observed on sodium dodecyl sulfate polyacrylamide gel electrophoresis. The enzyme contains 5.62 nmol covalently bound flavin and 3.79 nmol cytochrome b per mg protein. The 64.9 kDa subunit was shown to be a flavoprotein by its fluorescence. Polyclonal antibodies raised against this protein cross-reacted with the flavoprotein subunit of bovine heart mitochondrial succinate-ubiquinone reductase. The 28.9 kDa subunit is likely analogous to the bovine heart iron protein, and the cytochrome b heme is probably associated with one or both of the low-molecular-weight polypeptides. The cytochrome b is not reducible with succinate but is reoxidized with fumarate after prereduction with dithionite. Iron-sulfur clusters S-1 and S-3 of the Paracoccus oxidoreductase exhibit EPR spectra very similar to their mitochondrial counterparts. Paracoccus succinate-ubiquinone reductase complex is thus similar to the bovine heart mitochondrial enzyme with respect to prosthetic groups, enzymatic activity, inhibitor sensitivities, and polypeptide subunit composition.

Studies on the succinate dehydrogenating system. Interaction of the mitochondrial succinate-ubiquinone reductase with pyridoxal phosphate

The inhibitory effect of pyridoxal phosphate on the Triton X-100 solubilized purified bovine heart succinate-ubiquinone reductase (Choudhry, Z.M., Gavrikova, E.V., Kotlyar, A.B., Tushurashvilli, P.R. and Vinogradov, A.D. (1985) FEBS Lett. 182, 171-175) was studied. The kinetics of the enzyme inactivation by pyridoxal phosphate was found to be strongly dependent both qualitatively and quantitatively on the concentration of the protein-detergent complexes. In the diluted system the inactivation of the ubiquinone-depleted enzyme was completely prevented by the saturating concentrations of Q2, carboxin, thenoiltrifluoroacetone and pentachlorophenol, i.e., by the substrate and specific inhibitors of the enzyme. The protective effects of Q2 and the inhibitors was employed to quantitate the affinities of the ligands to their specific binding sites. Strong difference in the affinity of Q2 to the reduced and oxidized enzyme was found. When the soluble reconstitutively active succinate dehydrogenase was treated with pyridoxal phosphate, the reactivity of the enzyme towards low ferricyanide concentrations and its reconstitutive activity was significantly protected against aerobic inactivation.

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.

Pyridoxal phosphate-induced dissociation of the succinate: ubiquinone reductase

Treatment of the soluble ubiquinone-deficient succinate: ubiquinone reductase with pyridoxal phosphate results in the inhibition of the carboxin-sensitive ubiquinone-reductase activity of the enzyme. The inactivation is prevented by the soluble homolog of ubiquinone (Q2) but is insensitive to the dicarboxylates interacting with the substrate binding site of succinate dehydrogenase. The reactivity of the pyridoxal phosphate-inhibited enzyme with different electron acceptors suggests that the observed inhibition is due to the dissociation of succinate dehydrogenase from the enzyme complex. The soluble succinate dehydrogenase was recovered in the supernatant after treatment of the insoluble succinate: ubiquinone reductase with pyridoxal phosphate. The data obtained strongly suggest the participation of amino groups in the interaction between succinate dehydrogenase and the ubiquinone reactivity conferring peptide within the 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.

Mitochondrial genetics of mammalian cells: a mouse antimycin-resistant mutant with a probable alteration of cytochrome b

Mouse LA9 antimycin-resistant mutants (ANT-R) were isolated and characterized. Genetic analyses established that this phenotype is encoded within the mtDNA: (1) the ANT-R phenotype showed frequent mitotic segregation and reassortment in hybrid clonal lines; (2) it was transmitted directly in cybrid crosses; and (3) it was cotransmitted in cybrid crosses with the mitochondrial CAP-R marker. Furthermore, the genetic studies suggested that the LA9 CAP-R ANT-R cells were heteroplasmic and contained at least two mtDNA genotypes, cap-r ant-s and cap-s ant-r. Cellular respiration of the ANT-R mutant was markedly more resistant to inhibition by antimycin than that of the parental ANT-S cells. The increased resistance of cellular respiration was entirely accounted for by an increase in the resistance of mitochondrial succinate-cytochrome c oxidoreductase to antimycin inhibition. There was no detectable change in the specific activity of the oxidoreductase in mitochondria of resistant ANT-R cells nor in the sensitivity of the complex to three other specific inhibitors of the complex: TTFA, myxothiazol, and HQNO. Taken together, these studies indicate that the ANT-R phenotype is most likely encoded within the mitochondrial cytochrome b gene and, more specifically, within an antimycin binding domain.

Dietary lipid modulation of rat liver mitochondrial succinate: cytochrome c reductase

Diets supplemented with high levels of either saturated fatty acids or unsaturated fatty acids were fed to adult rats for a period of 9 weeks and changes in the liver mitochondrial membrane phospholipid fatty acid composition and thermal behaviour of succinate: cytochrome c reductase were determined. The dietary treatment induced a change in the omega 6 to omega 3 unsaturated fatty acid ratio in the membrane lipids, with the ratio being highest with the unsaturated fatty acid and lowest with the saturated fatty acid diet. Arrhenius plots of succinate: cytochrome c reductase activity exhibited differences in both critical temperature (Tf) and Arrhenius activation energy (Ea) depending on the type of dietary treatment. The Tf was elevated from 23 degrees C in control to 32 degrees C in the saturated fatty acid-supplemented group. No significant effect on the Tf was observed in the unsaturated fatty acid-supplemented group however higher Ea values were observed due to the unsaturated fatty acid diet. The changes in succinate: cytochrome c reductase are probably due to changes in the lipid-protein interactions in the membrane, induced by the dietary lipid supplementation.

Kinetics of ubiquinone reduction by the resolved succinate: ubiquinone reductase

A significant lag in the thenoyltrifluoroacetone (TTFA)-sensitive succinate: ubiquinone reductase activity was observed when a ubiquinone-deficient resolved preparation of the enzyme was assayed in the presence of exogenous ubiquinone-2 (Q2) and 2,6-dichlorophenolindophenol. No such lag was seen when the free radical of N,N,N',N'-tetramethyl-p-phenylenediamine (Wurster's Blue) was used as the terminal electron acceptor, or when the reduction of Q2 was directly measured. The apparent Km value for exogenous Q2 was determined in the Q2-mediated TTFA-sensitive succinate: Wurster's Blue reductase reaction. When the enzyme activity was measured directly by monitoring Q2 reduction without terminal acceptors, the time course of the reaction deviated from zero-order kinetics at Q2 concentrations which were much higher than those expected from the KQ2m value determined in the presence of Wurster's Blue. The time course of Q2 reduction fits a curve describing a competitive interrelationship between oxidized and reduced Q2 at the specific binding site. The data obtained are in agreement with the Q-pool behavior of ubiquinone in mitochondrial membranes and suggest that the rate of ubiquinone reduction by succinate is dependent on the Q/QH2 ratio.

The function of the subunits of the fumarate reductase complex of Vibrio succinogenes

The membrane-bound fumarate reductase complex of Vibrio succinogenes catalyzes the reduction of fumarate by 2,3-dimethyl-1,4-naphthohydroquinone (dimethylnaphthohydroquinone) and consists of three different peptides (Mr 79,000, Mr 31,000 and Mr 25,000), the smallest of which is cytochrome b [Unden, G., Hackenberg, H. and Kröger A. (1980) Biochem. Biophys. Acta 591, 275-288]. The complex was cleaved with guanidinium chloride, the resulting subunits characterized and their functions within the complex investigated by reconstitutional experiments. 1. The Mr-79,000 subunits catalyzed the reduction of fumarate by benzylviologen radicals as well as the oxidation of succinate by methylene blue, but not fumarate reduction by dimethylnaphthohydroquinone. 2. The spectral and the redox properties of the isolated cytochrome b (Mr 25,000) were equivalent to those of the high-potential cytochrome b of the bacteria. The isolated cytochrome b had a midpoint potential of -15 mV and was reducible by dimethylnaphthohydroquinone in the absence of the other subunits. 3. The Mr-31,000 subunit did not catalyze any of the reactions mentioned above. For the reduction of cytochrome b by succinate in the presence of the Mr-79,000 subunit, an amount of the Mr-31,000 subunit was required which was equimolar to cytochrome b. 4. The activity of fumarate reduction by dimethylnaphthohydroquinone could be restored by coprecipitation of the three subunits. It is concluded that the fumarate reductase complex has two different sites, which are essential for its function in the phosphorylative electron transport of the bacterium. The site reacting with the substrates fumarate and succinate is situated on the Mr-79,000 subunit, and that reacting with dimethylnaphthohydroquinone is cytochrome b. The Mr-31,000 subunit mediates the electron transport between cytochrome b and the Mr-79,000 subunit.

The participation of primary amino groups of succinate dehydrogenase in the formation of succinate-Q reductase

(1) Purified succinate dehydrogenase contains about 49 mol of lysine residues per mol enzyme. Titration of succinate dehydrogenase with fluorescamine indicates that half the lysyl groups are located on the surface of the protein and the other half are buried inside. (2) The reconstitutive activity and the low Km ferricyanide reductase activity of succinate dehydrogenase decreased as the extent of alkylation of amino groups by fluorescamine increased. (3) The inhibitory effects of fluorescamine on both activities are parallel and are succinate concentration dependent. (4) Alkylation of the native succinate-Q reductase by fluorescamine does not affect the enzymatic activity or alter the enzyme kinetic parameters. This indicates that the inhibitory effect of fluorescamine on succinate dehydrogenase is due to the modification of a specific amino group(s) on succinate dehydrogenase which is essential in the interaction with QPs to form succinate-Q reductase. The participation of an ionic group in the formation of succinate-Q reductase supports the idea of the involvement of ionic interaction between succinate dehydrogenase and QPs.