Control of mitochondrial superoxide production by reverse electron transport at complex I (original) (raw)
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AJP: Cell Physiology, 2007
Cardiac ischemia decreases complex III activity, cytochrome c content, and respiration through cytochrome oxidase in subsarcolemmal mitochondria (SSM) and interfibrillar mitochondria (IFM). The reversible blockade of electron transport with amobarbital during ischemia protects mitochondrial respiration and decreases myocardial injury during reperfusion. These findings support that mitochondrial damage occurs during ischemia and contributes to myocardial injury during reperfusion. The current study addressed whether ischemic damage to the electron transport chain (ETC) increased the net production of reactive oxygen species (ROS) from mitochondria. SSM and IFM were isolated from 6-mo-old Fisher 344 rat hearts following 25 min global ischemia or following 40 min of perfusion alone as controls. H2O2 release from SSM and IFM was measured using the amplex red assay. With glutamate as a complex I substrate, the net production of H2O2 was increased by 178 ± 14% and 179 ± 17% in SSM and IFM...
Cardiac Mitochondria and Reactive Oxygen Species Generation
Circulation Research, 2014
Mitochondrial reactive oxygen species (ROS) have emerged as an important mechanism of disease and redox signaling in the cardiovascular system. Under basal or pathological conditions, electron leakage for ROS production is primarily mediated by the electron transport chain and the proton motive force consisting of a membrane potential (ΔΨ) and a proton gradient (ΔpH). Several factors controlling ROS production in the mitochondria include flavin mononucleotide and flavin mononucleotide–binding domain of complex I, ubisemiquinone and quinone-binding domain of complex I, flavin adenine nucleotide–binding moiety and quinone-binding pocket of complex II, and unstable semiquinone mediated by the Q cycle of complex III. In mitochondrial complex I, specific cysteinyl redox domains modulate ROS production from the flavin mononucleotide moiety and iron–sulfur clusters. In the cardiovascular system, mitochondrial ROS have been linked to mediating the physiological effects of metabolic dilation...
Ubisemiquinone is the electron donor for superoxide formation by complex III of heart mitochondria*1
Archives of Biochemistry and Biophysics, 1985
Much evidence indicates that superoxide is generated from Oz in a cyanide-sensitive reaction involving a reduced component of complex III of the mitochondrial respiratory chain, particularly when antimycin A is present. Although it is generally believed that ubisemiquinone is the electron donor to Oz, little experimental evidence supporting this view has been reported. Experiments with succinate as electron donor in the presence of antimycin A in intact rat heart mitochondria, which contain much superoxide dismutase but little catalase, showed that myxothiazol, which inhibits reduction of the Rieske iron-sulfur center, prevented formation of hydrogen peroxide, determined spectrophotometrically as the HzOz-peroxidase complex. Similarly, depletion of the mitochondria of their cytochrome c also inhibited formation of Hz02, which was restored by addition of cytochrome c. These observations indicate that factors preventing the formation of ubisemiquinone also prevent Hz02 formation. They also exclude ubiquinol, which remains reduced under these conditions, as the reductant of Oz. Since cytochrome b also remains fully reduced when myxothiazol is added to succinate-and antimycin A-supplemented mitochondria, reduced cytochrome b may also be excluded as the reductant of OZ. These observations, which are consistent with the Q-cycle reactions, by exclusion of other possibilities leave ubisemiquinone as the only reduced electron carrier in complex III capable of reducing Oz to 0;. o 1985 Academic Press, Inc.
Mitochondrial respiration scavenges extramitochondrial superoxide anion via a nonenzymatic mechanism
Journal of Clinical Investigation, 1995
We determined that mitochondrial respiration reduced cytosolic oxidant stress in vivo and scavenged extramitochondrial superoxide anion (0) in vitro. First, Saccharomyces cerevisiae deficient in both the cytosolic antioxidant cuprozinc superoxide dismutase (CuZn-SOD) and electron transport (Rho°state) grew poorly (P < 0.05) in 21% 02 compared with parent yeast and yeast deficient only in electron transport or CuZn-SOD, whereas anaerobic growth was the same (P > 0.05) in all yeast. Second, isolated yeast and mammalian mitochondria scavenged extramitochondrial°2 generated by xanthine/xanthine oxidase. Yeast mitochondria scavenged 42% more (P < 0.05) extramitochondrial 0 2 during pyruvate/malate-induced respiration than in the resting state. Addition of either antimycin (respiratory chain inhibitor) or FCCP (respiratory chain uncoupler) prevented increased 0 scavenging. Mitochondria isolated from yeast deficient in the mitochondrial manganous superoxide dismutase (Mn-SOD) increased (P < 0.05)°2 scavenging 56% during respiration. This apparent SOD activity, expressed in units of SOD activity per milligram of mitochondrial protein, was the same (9±0.6 vs. 10±1.0; P-= 0.43) as the O2 scavenging of mitochondria with Mn-SOD, suggesting that respiration-dependent mitochondrial O 2 scavenging was nonenzymatic. Finally, isolated rat liver and lung mitochondria also increased (P < 0.05) 0 2 scavenging during respiration. We speculate that respiring mitochondria, via the protomnotive pump, present a polarized, proton-rich surface that enhances nonenzymatic dismutation of extramitochondrial O 2 and that this is a previously unrecognized function of mitochondrial respiration with potential physiological ramifications. (J. Clin. Invest. 1995.
Opening mitoKATP increases superoxide generation from complex I of the electron transport chain
AJP: Heart and Circulatory Physiology, 2006
Opening the mitochondrial ATP-sensitive K+ channel (mitoKATP) increases levels of reactive oxygen species (ROS) in cardiomyocytes. This increase in ROS is necessary for cardioprotection against ischemia-reperfusion injury; however, the mechanism of mitoKATP-dependent stimulation of ROS production is unknown. We examined ROS production in suspensions of isolated rat heart and liver mitochondria, using fluorescent probes that are sensitive to hydrogen peroxide. When mitochondria were treated with the KATP channel openers diazoxide or cromakalim, their ROS production increased by 40–50%, and this effect was blocked by 5-hydroxydecanoate. ROS production exhibited a biphasic dependence on valinomycin concentration, with peak production occurring at valinomycin concentrations that catalyze about the same K+ influx as KATP channel openers. ROS production decreased with higher concentrations of valinomycin and with all concentrations of a classical protonophoretic uncoupler. Our studies sho...
2011
Reactive oxygen species (ROS) produced in the mitochondrial respiratory chain (RC) are primary signals that modulate cellular adaptation to environment, and are also destructive factors that damage cells under the conditions of hypoxia/ reoxygenation relevant for various systemic diseases or transplantation. The important role of ROS in cell survival requires detailed investigation of mechanism and determinants of ROS production. To perform such an investigation we extended our rule-based model of complex III in order to account for electron transport in the whole RC coupled to proton translocation, transmembrane electrochemical potential generation, TCA cycle reactions, and substrate transport to mitochondria. It fits respiratory electron fluxes measured in rat brain mitochondria fueled by succinate or pyruvate and malate, and the dynamics of NAD + reduction by reverse electron transport from succinate through complex I. The fitting of measured characteristics gave an insight into the mechanism of underlying processes governing the formation of free radicals that can transfer an unpaired electron to oxygen-producing superoxide and thus can initiate the generation of ROS. Our analysis revealed an association of ROS production with levels of specific radicals of individual electron transporters and their combinations in species of complexes I and III. It was found that the phenomenon of bistability, revealed previously as a property of complex III, remains valid for the whole RC. The conditions for switching to a state with a high content of free radicals in complex III were predicted based on theoretical analysis and were confirmed experimentally. These findings provide a new insight into the mechanisms of ROS production in RC.
Antioxidants & Redox Signaling, 2014
Significance: Oxidative stress is a well established hallmark of cardiovascular disease and there is strong evidence for a causal role of reactive oxygen and nitrogen species (RONS) therein. Recent Advances: Improvement of cardiovascular complications by genetic deletion of RONS producing enzymes and overexpression of RONS degrading enzymes proved the involvement of these species in cardiovascular disease at a molecular level. Vice versa, overexpression of RONS producing enzymes as well as deletion of antioxidant enzymes was demonstrated to aggravate cardiovascular complications. Critical Issues: With the present overview we present and discuss different pathways how mitochondrial RONS interact (crosstalk) with other sources of oxidative stress, namely NADPH oxidases, xanthine oxidase and an uncoupled nitric oxide synthase. The potential mechanisms of how this crosstalk proceeds are discussed in detail. Several examples from the literature are summarized (including hypoxia, angiotensin II mediated vascular dysfunction, cellular starvation, nitrate tolerance, aging, hyperglycemia, b-amyloid stress and others) and the underlying mechanisms are put together to a more general concept of redox-based activation of different sources of RONS via enzyme-specific ''redox switches''. Mitochondria play a key role in this concept providing redox triggers for oxidative damage in the cardiovascular system but also act as amplifiers to increase the burden of oxidative stress. Future Directions: Based on these considerations, the characterization of the role of mitochondrial RONS formation in cardiac disease as well as inflammatory processes but also the role of mitochondria as potential therapeutic targets in these pathophysiological states should be addressed in more detail in the future. Antioxid. Redox Signal. 20, 308-324.