ArticleLiterature Review

Supercomplex organization of the mitochondrial respiratory chain and the role of the Coenzyme Q pool: Pathophysiological implications

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Abstract

In this review we examine early and recent evidence for an aggregated organization of the mitochondrial respiratory chain. Blue Native Electrophoresis suggests that in several types of mitochondria Complexes I, III and IV are aggregated as fixed supramolecular units having stoichiometric proportions of each individual complex. Kinetic evidence by flux control analysis agrees with this view, however the presence of Complex IV in bovine mitochondria cannot be demonstrated, presumably due to high levels of free Complex. Since most Coenzyme Q appears to be largely free in the lipid bilayer of the inner membrane, binding of Coenzyme Q molecules to the Complex I-III aggregate is forced by its dissociation equilibrium; furthermore free Coenzyme Q is required for succinate-supported respiration and reverse electron transfer. The advantage of the supercomplex organization is in a more efficient electron transfer by channelling of the redox intermediates and in the requirement of a supramolecular structure for the correct assembly of the individual complexes. Preliminary evidence suggests that dilution of the membrane proteins with extra phospholipids and lipid peroxidation may disrupt the supercomplex organization. This finding has pathophysiological implications, in view of the role of oxidative stress in the pathogenesis of many diseases.

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... Further, CoQ is essential for the assembly of complex III in yeast [47]. Although it has been long time considered that different CoQ pools are present in mitochondria, one linked to proteins and other free in the membrane, CoQ is also essential for the assembly of individual complexes, especially I, III and IV, into supercomplexes [48]. ...
... In fact, recent studies indicate that CoQ is essential in the structure of mitochondrial supercomplexes [21,49]. Formation of supercomplexes permits a more efficient electron transfer through the individual complexes [48], reduces the production of ROS and permits a more balanced activity of the mitochondrial electron transport chain. Interestingly, in rat heart, supercomplexes show a decline during aging [50] and this destabilization causes lower oxidative capacity and is responsible of a higher superoxide production [51]. ...
Article
Coenzyme Q (CoQ) is a key component for many essential metabolic and antioxidant activities in cells in mitochondria and cell membranes. Mitochondrial dysfunction is one of the hallmarks of aging and age-related diseases. Deprivation of CoQ during aging can be the cause or the consequence of this mitochondrial dysfunction. In any case, it seems clear that aging-associated CoQ deprivation accelerates mitochondrial dysfunction in these diseases. Non-genetic prolongevity interventions, including CoQ dietary supplementation, can increase CoQ levels in mitochondria and cell membranes improving mitochondrial activity and delaying cell and tissue deterioration by oxidative damage. In this review, we discuss the importance of CoQ deprivation in aging and age-related diseases and the effect of prolongevity interventions on CoQ levels and synthesis and CoQ-dependent antioxidant activities.
... Recently, it has been indicated that OPA1, a regulator of the fusion of the mitochondrial outer membrane, mediates the regulation of complex IV activity through a CoQ-dependent procedure [71]. Interestingly, a pool of CoQ is associated with complex I + III + IV supercomplexes, whereas free CoQ is dedicated to complex II-dependent respiratory chain activity [72][73][74]. This is very important as supercomplexes are associated with a balanced ETC chain activity and point to the regulatory role of CoQ in their assembly dynamics [70,75,76]. ...
Article
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Coenzyme Q is a unique lipidic molecule highly conserved in evolution and essential to maintaining aerobic metabolism. It is endogenously synthesized in all cells by a very complex pathway involving a group of nuclear genes that share high homology among species. This pathway is tightly regulated at transcription and translation, but also by environment and energy requirements. Here, we review how coenzyme Q reacts within mitochondria to promote ATP synthesis and also integrates a plethora of metabolic pathways and regulates mitochondrial oxidative stress. Coenzyme Q is also located in all cellular membranes and plasma lipoproteins in which it exerts antioxidant function, and its reaction with different extramitochondrial oxidoreductases contributes to regulate the cellular redox homeostasis and cytosolic oxidative stress, providing a key factor in controlling various apoptosis mechanisms. Coenzyme Q levels can be decreased in humans by defects in the biosynthesis pathway or by mitochondrial or cytosolic dysfunctions, leading to a highly heterogeneous group of mitochondrial diseases included in the coenzyme Q deficiency syndrome. We also review the importance of coenzyme Q levels and its reactions involved in aging and age-associated metabolic disorders, and how the strategy of its supplementation has had benefits for combating these diseases and for physical performance in aging.
... Mitochondria exhibit a double-membrane structure and are the major responsible for the synthesis of adenosine triphosphate (ATP) in mammalian cells [15,16]. Moreover, several other reactions involved in the maintenance of metabolism in mammalian cells occur in the mitochondria, such as gluconeogenesis and urea cycle [17], among others. ...
Article
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Carnosic acid (CA; C20H28O4), a phenolic diterpene characterized as an ortho-dihydroquinone-type molecule, is a pro-electrophile agent that becomes an electrophile after reacting with free radicals. The electrophile generated from CA interacts with and activates the nuclear factor erythroid 2-related factor 2 (Nrf2) transcription factor, which is a major modulator of redox biology in mammalian cells. CA induces antioxidant and anti-inflammatory effects in several cell types, as observed in both in vitro and in vivo experimental models. In this context, CA has been viewed as a neuroprotective agent by activating signaling pathways associated with cell survival during stressful conditions. Indeed, CA exhibits the ability to promote mitochondrial protection in neural cells. Mitochondria are the main source of both ATP and reactive species in animal cells. Mitochondrial dysfunction plays a central role in the start and development of neurodegenerative disorders, such as Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease, among others. Therefore, the study of strategies aiming to reduce mitochondrial impairment in the case of neurodegeneration is of pharmacological interest. In the present review, it is described and discussed the effects of CA on brain mitochondria in experimental models of neural lesion. Based on the data discussed here, CA is a potential candidate to be listed as a neuroprotective agent by acting on the mitochondria of neural cells.
... Kinetic and structural analysis of the mammalian mitochondrial respiratory chain suggests that the individual Complexes I-IV (NADH:ubiquinone oxidoreductase, succinate:ubiquinone oxidoreductase, bc 1 complex (ubiqunol:cytochrome c oxidoreductase), and cytochrome c oxidase, respectively) exist in mitochondria under physiological conditions in equilibrium with supercomplexes or " respirasomes " composed of all of the above individual complexes (see (Mileykovskaya et al., 2005) for references). Depending on metabolic conditions electron transfer in the respiratory chain would occur (1) via substrate channeling of the small carriers, (ubiquinone, between Complexes I (or II) and III or cytochrome c between Complexes III and IV) due to supercomplex formation or (2) via random diffusion of these small carriers between individual complexes independently imbedded in the lipid bilayer (Genova et al., 2005). In S. cerevisiae mitochondria this equilibrium appears to be shifted to supercomplex organization of Complexes III and IV (Mileykovskaya et al., 2005), which may also contain Complex II as well as two peripheral NADH dehydrogenases (Boumans et al., 1998); S. cerevisiae lack Complex I and utilize the peripheral NADH dehydrogenases. ...
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Lipids play important roles in cellular dysfunction leading to disease. Although a major role for phospholipids is in defining the membrane permeability barrier, phospholipids play a central role in a diverse range of cellular processes and therefore are important factors in cellular dysfunction and disease. This review is focused on the role of phospholipids in normal assembly and organization of the membrane proteins, multimeric protein complexes, and higher order supercomplexes. Since lipids have no catalytic activity, it is difficult to determine their function at the molecular level. Lipid function has generally been defined by affects on protein function or cellular processes. Molecular details derived from genetic, biochemical, and structural approaches are presented for involvement of phosphatidylethanolamine and cardiolipin in protein organization. Experimental evidence is presented that changes in phosphatidylethanolamine levels results in misfolding and topological misorientation of membrane proteins leading to dysfunctional proteins. Examples are presented for diseases in which proper protein folding or topological organization is not attained due to either demonstrated or proposed involvement of a lipid. Similar changes in cardiolipin levels affects the structure and function of individual components of the mitochondrial electron transport chain and their organization into supercomplexes resulting in reduced mitochondrial oxidative phosphorylation efficiency and apoptosis. Diseases in which mitochondrial dysfunction has been linked to reduced cardiolipin levels are described. Therefore, understanding the principles governing lipid-dependent assembly and organization of membrane proteins and protein complexes will be useful in developing novel therapeutic approaches for disorders in which lipids play an important role.
... Subsequently, ubiquinol is oxidized by complex III. The electrons are then transferred to cytochrome C, which is then oxidized by complex IV by reducing O 2 to H 2 O [12]. Complexes III and IV can translocate protons across the inner mitochondrial membrane throughout electron transfer, resulting in a proton gradient that drives ATP synthesis by complex V. ...
Article
To investigate the effect of anaerobiosis on the Saccharomyces cerevisiae mitochondrial proteome and the formation of respiratory chain and other protein complexes, we analyzed mitochondrial protein extracts that were enriched from lysates of aerobic and anaerobic steady-state chemostat cultures. We chose an innovative approach in which native mitochondrial membrane protein complexes were separated by 1-D blue native PAGE, which was combined with quantitative analysis of each complex subunit using stable isotope labeling. LC-FT(ICR)-MS/MS analysis was applied to identify and quantify the mitochondrial proteins. In addition, to establish if changes in mitochondrial complex composition occurred under anaerobiosis, we investigated the 1-D blue native PAGE protein migration patterns by Pearson correlation analysis. Surprisingly, we discovered that under anaerobic conditions, where the yeast respiratory chain is not active, the respiratory chain supercomplexes, such as complex V dimer, complex (III)(2)(IV)(2) and complex (III)(2)(IV) were still present, although at reduced levels. Pearson correlation analysis showed that the composition of the mitochondrial complexes was unchanged under aerobic or anaerobic conditions, with the exception of complex II. In addition, this latter approach allowed screening for possible novel complex interaction partners, since for example protein Aim38p, with a yet unknown function, was identified as a possible component of respiratory chain complex IV.
... Most likely the activity of these integral membrane enzymes is impaired due to changes in membrane fluidity [159] produced by lipid peroxidation. Moreover, it has been reported that oxidative stress is particularly deleterious for enzymes associated with electron transport chains such as desaturases [160]. Firstly, changes in intracellular redox potential disrupt the homeostatic balance of released and accepted electrons. ...
Article
Non-alcoholic fatty liver disease (NAFLD) has a high occurrence in most countries. Recent studies estimate its prevalence to be near 30% in United States, Italian and Japanese general adult populations. NAFLD commonly presents along with obesity and insulin resistance (IR), pathologies that share with NAFLD metabolic and inflammatory components. These conditions, particularly NAFLD, are associated with alterations in the bioavailability of long-chain polyunsaturated fatty acids (LCPUFAs). In the human population, the bioavailability of LCPUFAs depends both on endogenous biosynthesis and diet amount of preformed LCPUFAs. However, the lower liver LCPUFAs product/precursor ratio namely (20:5n-3+22:6n-3)/18:3n-3, 20:4n-6/18:2n-6 present in common Western diets, makes critical an adequate pathway activity to ensure minimum bioavailability of LCPUFAs in most Western populations. The key step of this biosynthesis involves Δ5 and Δ6-desaturases, whose activities are altered in NAFLD. During the disease, the presence of molecular activators of these two enzymes does not correlate with the scarce LCPUFAS biosynthesis observed. The key to this apparent contradiction, or at least part of it, could be explained on the basis of the possible sensitivity of the desaturases to oxidative stress; a metabolic condition strongly linked to inflammatory pathologies such as NAFLD, obesity and IR and that, according to latest research, not only would be consequence but also possibly a cause of these diseases. The present review is focused on the relationship between NAFLD and the bioavailability of LCPUFAs, with special reference to the role that oxidative stress could play in the modulation of the liver fatty acid desaturase activity.
... This is in accordance with our data on stability of CO I and supercomplexes in these two mutants. Mutual interdependency of CO I, III and IV in respiratory supercomplexes is clearly established [31]. It is far less clear what is complex II role in this and what would be the consequences of its upregulation on the stoichiometry of supercomplexes. ...
Article
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Many Caenorhabditis elegans mutants with dysfunctional mitochondrial electron transport chain are surprisingly long lived. Both short-lived (gas-1(fc21)) and long-lived (nuo-6(qm200)) mutants of mitochondrial complex I have been identified. However, it is not clear what are the pathways determining the difference in longevity. We show that even in a short-lived gas-1(fc21) mutant, many longevity assurance pathways, shown to be important for lifespan prolongation in long-lived mutants, are active. Beside similar dependence on alternative metabolic pathways, short-lived gas-1(fc21) mutants and long-lived nuo-6(qm200) mutants also activate hypoxia-inducible factor -1α (HIF-1α) stress pathway and mitochondrial unfolded protein response (UPR(mt)). The major difference that we detected between mutants of different longevity, is in the massive loss of complex I accompanied by upregulation of complex II levels, only in short-lived, gas-1(fc21) mutant. We show that high levels of complex II negatively regulate longevity in gas-1(fc21) mutant by decreasing the stability of complex I. Furthermore, our results demonstrate that increase in complex I stability, improves mitochondrial function and decreases mitochondrial stress, putting it inside a "window" of mitochondrial dysfunction that allows lifespan prolongation.
... In particular, mutant fibroblasts with moderate deficiency (30-50% UQ 10 ) produce maximal oxidative stress, while ,20% residual UQ 10 is not associated with increased oxidative stress (25,63,74). The complexes of the mitochondrial respiratory chain can assemble into supermolecular structures called supercomplexes which allow more efficient and rapid electron transfer as opposed to a random collision model (75,76). Supercomplex formation is thought to be a very dynamic process and of great importance for regulation of mitochondrial bioenergetics and controlling ROS production (77). ...
Article
Ubiquinone (UQ), a.k.a. coenzyme Q, is a redox-active lipid that participates in several cellular processes, in particular mitochondrial electron transport. Primary UQ deficiency is a rare but severely debilitating condition. Mclk1 (a.k.a. Coq7) encodes a conserved mitochondrial enzyme that is necessary for UQ biosynthesis. We engineered conditional Mclk1 knockout models to study pathogenic effects of UQ deficiency and to assess potential therapeutic agents for the treatment of UQ deficiencies. We found that Mclk1 knockout cells are viable in the total absence of UQ. The UQ biosynthetic precursor DMQ9 accumulates in these cells and can sustain mitochondrial respiration, albeit inefficiently. We demonstrated that efficient rescue of the respiratory deficiency in UQ-deficient cells by UQ analogues is sidechain length-dependent, and that classical UQ analogues with alkyl sidechains such as idebenone and decylUQ are inefficient in comparison to analogues with isoprenoid sidechains. Furthermore, Vitamin K2, which has an isoprenoid sidechain, and has been proposed to be a mitochondrial electron carrier, had no efficacy on UQ-deficient mouse cells. In our model with liver-specific loss of Mclk1, a large depletion of UQ in hepatocytes caused only a mild impairment of respiratory chain function and no gross abnormalities. In conjunction with previous findings, this surprisingly small effect of UQ depletion indicates a non-linear dependence of mitochondrial respiratory capacity on UQ content. With this model we also showed that diet-derived UQ10 is able to functionally rescue the electron transport deficit due to severe endogenous UQ deficiency in the liver, an organ capable of absorbing exogenous UQ.
... The proportion of the different ratios between free complexes and supercomplexes depends on cell type and metabolic state. The plasticity model allows the explanation of previous observations such as the dependence between complex I stability and complex III [18] or IV [19][20][21] physical presence, the different supercomplexes proportions in different cell types or the kinetic studies supporting the existence of different CoQ pools [22,23]. ...
Article
Two alternative models of organization of the mitochondrial electron transport chain (mETC) have been alternatively favored or questioned by the accumulation evidences of different sources, the solid model or the random collision model. Both agree in the number of respiratory complexes (I-IV) that participate in the mETC, but while the random collision model proposes that Complexes I-IV do not interact physically and that electrons are transferred between them by coenzyme Q and cytochrome c, the solid model proposes that all complexes super-assemble in the so-called respirasome. Recently, the plasticity model has been developed to incorporate the solid and the random collision model as extreme situations of a dynamic organization, allowing super-assembly free movement of the respiratory complexes. In this review, we evaluate the supporting evidences of each model and the implications of the super-assembly in the physiological role of coenzyme Q.
... The proportion of the different ratios between free complexes and supercomplexes depends on cell type and metabolic state. The plasticity model allows the explanation of previous observations such as the dependence between complex I stability and complex III [18] or IV [19][20][21] physical presence, the different supercomplexes proportions in different cell types or the kinetic studies supporting the existence of different CoQ pools [22,23]. ...
Article
The evidence accumulated during the last fifteen years on the existence of respiratory supercomplexes and their proposed functional implications has changed our understanding of the OXPHOS system complexity and regulation. The plasticity model is a point of encounter accounting for the apparently contradictory experimental observations claimed to support either the solid or the fluid models. It allows the explanation of previous observations such as the dependence between respiratory complexes, supercomplex assembly dynamics or the existence of different functional ubiquinone pools. With the general acceptation of respiratory supercomplexes as true entities, this review evaluates the supporting evidences in favor or against the existence of different ubiquinone pools and the relationship between supercomplexes, ROS production and pathology.
... superkompleksy. Taka organizacja pozwala zwiększyć szybkość i wydajność transportu elektronów, a także ograniczyć powstawanie szkodliwych reaktywnych form tlenu (RFT) przez kompleks I [17,26,43]. W warunkach normoksji przepływ elektronów w łańcuchu oddechowym jest związany głównie z utlenianiem substratów związanych z NAD i odbywa się poprzez kompleks I. Szacuje się, że jest odpowiedzialny za 55-65% oddychania mitochondrialnego, pozostała część jest związana z aktywnością kompleksu II. ...
Article
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Neurons vary widely in shape, size, type of neurotransmitters and number of synapses. Their common characteristic is a very high sensitivity to changes in oxygen concentration. The consequence of hypoxia is to launch a series of biochemical reactions called the ischemic cascade. The term is a bit misleading, because it suggests that there is a succession of events, in a linear fashion. In fact, the ischemic cascade involves very complex processes that take place simultaneously and interact with each other. The key role in neuronal responses to hypoxia is played by changes related to mitochondria, which occur immediately after hypoxia, at the beginning of the ischemic cascade. Disturbances in the mitochondrial functions are recognized as an essential element not only in acute but also in chronic hypoxia, as well as neurodegenerative diseases.
... Supercomplexes are massive protein structures formed by various respiratory enzymes. As opposed to random collisions of the individual complexes, the advantage of such organization is a more efficient electron transfer and thereby restricted ROS generation during electron transfer reactions (Genova et al., 2005, Winge, 2012, Seelert et al., 2009. It is possible that under condition of severe UQ depletion, in order to sustain sufficient energy production, the mitochondrial respiratory chain may augment the electron transport via the respiratory supercomplexes, producing less ROS. ...
Article
Ubiquinone (UQ), also known as coenzyme Q (CoQ), is a redox-active lipid present in all cellular membranes where it functions in a variety of cellular processes. The best known functions of UQ are to act as a mobile electron carrier in the mitochondrial respiratory chain and to serve as a lipid soluble antioxidant in cellular membranes. All eukaryotic cells synthesize their own UQ. Most of the current knowledge on the UQ biosynthetic pathway was obtained by studying Escherichia coli and Saccharomyces cerevisiae UQ-deficient mutants. The orthologues of all the genes known from yeast studies to be involved in UQ biosynthesis have subsequently been found in higher organisms. Animal mutants with different genetic defects in UQ biosynthesis display very different phenotypes, despite the fact that in all these mutants the same biosynthetic pathway is affected. This review summarizes the present knowledge of the eukaryotic biosynthesis of UQ, with focus on the biosynthetic genes identified in animals, including Caenorhabditis elegans, rodents, and humans. Moreover, we review the phenotypes of mutants in these genes and discuss the functional consequences of UQ deficiency in general.
... It has been proposed that one of the functions of SCs is to allow for a more efficient electron transfer conferring kinetic advantage by substrate channeling. A more efficient electron transfer will avoid diffusion of intermediates that could prematurely react with oxygen to form free radicals such as superoxide [17,18]. SCs would also enhance the stability of respiratory complexes particularly of CI and would limit the production of reactive oxygen species (ROS) [19]. ...
Article
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We examine the effect of oxidative stress on the stability of mitochondrial respiratory complexes and their association into supercomplexes (SCs) in the neuron-specific Rieske iron sulfur protein (RISP) and COX10 knockout (KO) mice. Previously we reported that these two models display different grades of oxidative stress in distinct brain regions. Using blue native gel electrophoresis, we observed a redistribution of the architecture of SCs in KO mice. Brain regions with moderate levels of oxidative stress (cingulate cortex of both COX10 and RISP KO and hippocampus of the RISP KO) showed a significant increase in the levels of high molecular weight (HMW) SCs. High levels of oxidative stress in the piriform cortex of the RISP KO negatively impacted the stability of CI, CIII and SCs. Treatment of the RISP KO with the mitochondrial targeted antioxidant mitoTEMPO preserved the stability of respiratory complexes and formation of SCs in the piriform cortex and increased the levels of glutathione peroxidase. These results suggest that mild to moderate levels of oxidative stress can modulate SCs into a more favorable architecture of HMW SCs to cope with rising levels of free radicals and cover the energetic needs.
... Mitochondria utilize oxygen (O 2 ) gas as a final acceptor of electrons in the respiratory chain, which is composed by complex I (NADH dehydrogenase), complex II (succinate dehydrogenase (SDH)), complex III (ubiquinol-cytochrome c reductase), and complex IV (cytochrome c oxidase) (Chance and Williams 1955;Korzeniewski 1996;Papa et al. 2012). The complexes I, III, and IV pump protons from the mitochondrial matrix to the intermembrane space (IMS), which is located between the inner mitochondrial membrane (IMM) and the outer mitochondrial membrane (OMM) (Alvarez-Paggi et al. 2017;Genova et al. 2005;Genova and Lenaz 2011;Gibson et al. 2005;Nohl et al. 2003). The electrochemical gradient generated by the proton pumping is used by complex V to produce ATP from adenosine diphosphate (ADP) and inorganic phosphate (Pi) (Papa et al. 2012;Solaini et al. 2007). ...
Article
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Mitochondria are the major site of adenosine triphosphate (ATP) production in mammalian cells. Moreover, mitochondria produce most of the reactive oxygen species (ROS) in nucleated cells. Redox and bioenergetic abnormalities have been seen in mitochondria during the onset and progression of neurodegenerative diseases. In that context, excitotoxicity induced by glutamate (GLU) plays an important role in mediating neurotoxicity. Several drugs have been used in the treatment of diseases involving excitotoxicity. Nonetheless, some patients (20–30%) present drug resistance. Thus, it is necessary to find chemicals able to attenuate mitochondrial dysfunction in the case of excitotoxicity. In this work, we treated the human neuroblastoma SH-SY5Y cell line with the diterpene carnosic acid (CA) at 1 μM for 12 h prior to the exposure to GLU for further 24 h. We found that CA prevented the GLU-induced mitochondrion-related redox impairment and bioenergetic decline in SH-SY5Y cells. CA also downregulated the pro-apoptotic stimulus elicited by GLU in this experimental model. CA exerted mitochondrial protection by a mechanism associated with the transcription factor nuclear factor erythroid 2–related factor 2 (Nrf2), since silencing of this protein with small interfering RNA (siRNA) suppressed the CA-induced protective effects. Future directions include investigating whether CA would be able to modulate mitochondrial function and/or dynamics in in vivo experimental models of excitotoxicity.
... The proportion of the different ratios between free complexes and supercomplexes depends on cell type and metabolic state. The plasticity model allows the explanation of previous observations such as the dependence between complex I stability and complex III [18] or IV [19][20][21] physical presence, the different supercomplexes proportions in different cell types or the kinetic studies supporting the existence of different CoQ pools [22,23]. ...
Article
Electron transfer between respiratory complexes is an essential step for the efficiency of the mitochondrial oxidative phosphorylation. Until recently, it was stablished that ubiquinone and cytochrome c formed homogenous single pools in the inner mitochondrial membrane which were not influenced by the presence of respiratory supercomplexes. However, this idea was challenged by the fact that bottlenecks in electron transfer appeared after disruption of supercomplexes into their individual complexes. The postulation of the plasticity model embraced all these observations and concluded that complexes and supercomplexes co-exist and are dedicated to a spectrum of metabolic requirements. Here, we review the involvement of superassembly in complex I stability, the role of supercomplexes in ROS production and the segmentation of the CoQ and cyt c pools, together with their involvement in signaling and disease. Taking apparently conflicting literature we have built up a comprehensive model for the segmentation of CoQ and cyt c mediated by supercomplexes, discuss the current limitations and provide a prospect of the current knowledge in the field.
... However, the exact composition and functional role of the supercomplexes are still unclear [132][133][134][135][136][137][138] . Preliminary evidence suggests that mitochondrial membrane lipid composition and peroxidation may influence supercomplex organization 139 . In particular, cardiolipin is considered to be an important factor anchoring the supercomplex in the mitochondrial inner-membrane 140 . ...
Article
Obesity‐induced insulin resistance and type 2 diabetes mellitus can ultimately result in various complications, including diabetic cardiomyopathy. In this case, cardiac dysfunction is characterized by metabolic disturbances such as impaired glucose oxidation and an increased reliance on fatty acid oxidation. Mitochondrial dysfunction has often been associated with the altered metabolic function in the diabetic heart, and may result from fatty acid‐induced lipotoxicity and uncoupling of oxidative phosphorylation. In this review, we address the metabolic changes in the diabetic heart, focusing on the loss of metabolic flexibility and cardiac mitochondrial function. We consider the alterations observed in mitochondrial substrate utilization, bioenergetics and dynamics, and highlight new areas of research which may improve our understanding of the cause and effect of cardiac mitochondrial dysfunction in diabetes. Finally, we explore how lifestyle (nutrition and exercise) and pharmacological interventions can prevent and treat metabolic and mitochondrial dysfunction in diabetes.
... Therefore, mitochondrial dysfunction may play a major role in AD aetiopathogenesis (Wang et al. 2009). Mitochondrion is a solo organelle responsible for the synthesis of ATP during respiratory chain activity in mammalian cells, and at the same time, it also produces ROS (Genova et al. 2005;Papa et al. 2012;Naoi et al. 2005). It also contains enzymes, i.e. monoamine oxidase (MAO) and nitric oxide synthase (NOS), in which the former produces the H 2 O 2 and the latter is responsible for the production of NO in the influence of neuroinflammtion (Brown and Bal-Price 2003;Pun et al. 2010;Venditti et al. 2013;Wilkins and Swerdlow 2016). ...
Chapter
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Rosemary (Rosmarinus officinalis L.), the representative of Lamiaceae family is known for its various medicinal uses that are accompanied by their hallmark secondary metabolites, i.e., carnosol, carnosic acid and rosmarinic acid (mostly the polyphenolic diterpenes). In the age of medicines and methodologies, when we are floating through the advancements and achievements, we are being hijacked by various diseases leading to increased number of young deaths. Neurological disorders are one of them and characterized by any impairment in the nervous system, brain or spinal cord. The majority of young and aged people around the globe are manifested by neurological disorders, i.e., stroke, epilepsy, dementia, Alzheimer’s disease (AD), Parkinson’s disease (PD) and migraine. A large number of therapeutic approaches mend the symptoms in early stages of these disorders, but with the span of time, patients become progressively more disabled as they may suffer from drug-associated adverse effects. Emphasizing on the urgent need of alternative therapeutic regimens, natural products are encouraged worldwide in terms of safety and to minimize the aforesaid loss. In this order, the current chapter summarizes the protective role of R. officinalis L. and its bio-active metabolites against various neurological disorders via targeting amyloid-beta (A-β) aggregation, neuronal cell death, acetylcholinesterase (AChE), neuroinflammation, β-secretase (BACE-1) activity, mitochondrial redox status, etc. Based on the multifunctional nature due to effective bio-active secondary metabolites, R. officinalis can be a terrific alternative therapeutic source against many neurodegenerative diseases.
... 21 Dysfunction in the assembly of MRC complexes in supercomplexes has been hypothesized to be affected in diseases and probably in aging, 22 and CoQ 10 could be an important factor in this dysfunction. 23 As a redox lipid, CoQ 10 shows antioxidant properties, 24 protecting cellular membranes, mainly plasma membrane, through the transplasma-membrane electron transport system 25 (Fig. 3). CoQ 10 is an antioxidant by itself or by maintaining α-tocopherol and vitamin C in their reduced states, which would contribute to extracellular and intramembrane oxidative damages. ...
Chapter
Coenzyme Q10 (CoQ10) is an essential factor for aerobic bioenergetics and antioxidant protection in cell membranes and blood plasma lipoproteins. It is a component of the electron transport chain in mitochondria and the trans plasma membrane electron transport. Its deficiency in human causes CoQ10 deficiency syndrome, a heterogeneous group of mitochondrial diseases. Decrease of CoQ10 levels has been also associated with aging progression and age-related diseases. Human supplementation with CoQ10 has improved the progression of age-dependent diseases and decreased the mortality caused by these diseases. Some of them are linked to oxidative damage such as cardiovascular disease and fibrosis. However, its use as supplement depends on its bioavailability and in the capacity to reach organs and tissues. Other strategies to increase endogenous CoQ10 biosynthesis during aging would be explored.
... The mitochondria present the molecular apparatus necessary to produce more than 90% of the adenosine triphosphate (ATP) in the nucleated human cells [10]. The electron transfer chain (ETC) contains the complexes I (NADH dehydrogenase), II (succinate dehydrogenase, SDH), III (coenzyme Q:cytochrome c-oxidoreductase), and IV (cytochrome c oxidase), as well as the electron transfer components ubiquinone (the so-called coenzyme Q 10 ) and cytochrome c (a heme protein) [11,12]. The flux of electrons in the ETC is utilized by the complexes to generate a proton (H + ) gradient across the inner mitochondrial membrane, which is measured as the mitochondrial membrane potential (MMP) experimentally [13]. ...
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The link between mitochondrial dysfunction, redox impairment, and inflammation leads to increased rates of brain cells loss in neurodegenerative diseases and in affective disorders. Carvacrol (CAR) is a component of essential oils found in Labiatae. CAR exerts antioxidant and anti-inflammatory effects in different cell types, as assessed in both in vitro and in vivo experimental designs. Nonetheless, it was not previously investigated whether and how CAR would prevent mitochondrial impairment in human cells exposed to a pro-oxidant challenge. Therefore, we analyzed here whether a pretreatment (for 4 h) with CAR (10–1000 µM) would promote mitochondrial protection in the human neuroblastoma cells SH-SY5Y exposed to hydrogen peroxide (H2O2). We found that CAR at 100 µM prevented the H2O2-induced decline in the activity of the complexes I and V, as well as on the levels of adenosine triphosphate (ATP). CAR also prevented the H2O2-elicited decrease in the activity of the mitochondrial enzymes aconitase, α-ketoglutarate dehydrogenase, and succinate dehydrogenase. Moreover, CAR induced an antioxidant action by decreasing the levels of lipid peroxidation, protein carbonylation, and protein nitration in the mitochondrial membranes. Interestingly, CAR prevented the pro-inflammatory action of H2O2 by downregulating the transcription factor nuclear factor-κB (NF-κB). The inhibition of the heme oxygenase-1 (HO-1) enzyme by zinc protoporphyrin IX (ZnPP IX, 10 µM) suppressed the preventive effects caused by CAR regarding mitochondrial function and inflammation. Thus, it is suggested that CAR caused cytoprotective effects by an HO-1-dependent manner in SH-SY5Y cells exposed to H2O2.
... The oxidative phosphorylation system comprises the respiratory chain and the complex V (ATP synthase/ATPase) enzyme) [5]. The complexes I (NADH dehydrogenase), II (succinate dehydrogenase), III (ubiquinol:cytochrome c oxidoreductase), and IV (cytochrome c oxidase) are the components of the respiratory chain [6,7]. The flux of electrons in the respiratory chain releases energy that is utilized by the complexes (with exception to the complex II) to pump protons from the mitochondrial matrix into the intermembrane space (IMS), which is an area between the inner mitochondrial membrane (IMM) and the outer mitochondrial membrane (OMM) [5]. ...
Article
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Mitochondria are double-membrane organelles involved in the transduction of energy from different metabolic substrates into adenosine triphosphate (ATP) in mammalian cells. The oxidative phosphorylation system is comprised by the activity of the respiratory chain and the complex V (ATP synthase/ATPase). This system is dependent on oxygen gas (O2) in order to maintain a flux of electrons in the respiratory chain, since O2 is the final acceptor of these electrons. Electron leakage from this complex system leads to the continuous generation of reactive species in the cells. The mammalian cells exhibit certain mechanisms to attenuate the consequences originated from the constant exposure to these reactive species. In this context, the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) and one of the enzymes whose expression is modulated by Nrf2, heme oxygenase-1 (HO-1), take a central role in inducing cytoprotection in humans. Mitochondrial abnormalities are observed during intoxication and in certain diseases, including neurodegeneration. Mitochondrial protection promoted by natural compounds has attracted the attention of researchers due to the promising effects these agents induce experimentally. In this regard, we examined here whether and how gastrodin (GAS), a phenolic glucoside, would prevent the paraquat (PQ)-induced mitochondrial impairment in the SH-SY5Y cells. The cells were exposed to GAS (25 μM) for 4 h prior to the challenge with PQ at 100 μM for additional 24 h. The silencing of Nrf2 by siRNA or the inhibition of HO-1 by ZnPP IX suppressed the GAS-elicited cytoprotection. Therefore, GAS promoted mitochondrial protection by an Nrf2/HO-1-dependent manner.
Article
The aim of this work was to study hepatic and muscular mitochondria function in response to chronic or acute exercise. We have simultaneously studied the mitochondrial oxygen consumption and free radical production based on the H2O2 production with Amplex Red as a probe. We have shown that a single bout of exercise increases free radical production that was persistent for 2 hours in muscle while it was delayed in liver. This free radical production appears to be tolerated by the mitochondria through the antioxidant pool that remained unaffected. Measurements with specific substrates and inhibitors on the electron transport chain that are useful to functionally isolate the different respiratory complexes allowed us to determine specific sites of adaptations. In a second part, we tested the effect of moderate chronic exercise that induced increases in mitochondrial density in muscle and more originally in liver, along with functional adaptations. Muscle mitochondria seems to have a better efficiency to extract reduced equivalents from fatty acids through a process named metabolic slipping. Liver mitochondria displayed an enhanced oxidation yield in ADP-stimulated respiratory status with complex I substrates. Results suggest that the decrease in mitochondrial functioning is compensated by the increase in the tissue mitochondrial density, as shown by parallel increases in CS activity. The sites of ROS production appear to be tissue specific. In fact, exercise appears to affect mostly the H2O2 production from complex III in muscle mitochondria but complex I in liver mitochondria. The use of PGC-1α antisense oligonucleotides, in order to decrease the PGC-1α protein expression, doesn't affect mitochondrial biogenesis induced by endurance training in muscle but totally inhibit the training-induced mitochondrial biogenesis in liver. Functional adaptations (i.e. altered respiratory control and ROS production) linked to the absence of this protein seem to confirm the essential role of PGC-1α in tissue-specific mitochondrial adaptations to exercise. These results suggest that free radicals could play a role by feedback control of PGC-1α, on exercise-induced mitochondrial adaptations.
Chapter
Oxidative stress has been related to osteoporosis and other pathologies at the bone. Coenzyme Q10 (CoQ10), a lipid-soluble antioxidant present in cell membranes, has been suggested in vitro to reduce intracellular reactive oxygen species (ROS) production at the same time to prevent or reduce osteoclastogenesis. Also, it promotes osteoblast differentiation and proliferation and matrix mineralization. Thus it has been suggested that this effect on osteoclastogenesis could be a consequence of the reduction of intracellular ROS. The protective effect of CoQ10 against bone loss has been also demonstrated in rodents. Age-associated changes in systemic markers of oxidative damage in animals treated with CoQ10 suggest that this antioxidant can reduce not only intracellular ROS alleviating oxidative damage but also osteoclastogenesis and bone resorption triggered by different signals. Additionally, it has been suggested that oxidative stress is the main mechanism explaining bone alterations both in aged rodents and in those with acute sex steroid deficiency.
Article
The evidence supporting a treatment benefit for coenzyme Q10 (CoQ10) in primary mitochondrial disease (mitochondrial disease) whilst positive is limited. Mitochondrial disease in this context is defined as genetic disease causing an impairment in mitochondrial oxidative phosphorylation (OXPHOS). There are no treatment trials achieving the highest Level I evidence designation. Reasons for this include the relative rarity of mitochondrial disease, the heterogeneity of mitochondrial disease, the natural cofactor status and easy 'over the counter availability' of CoQ10 all of which make funding for the necessary large blinded clinical trials unlikely. At this time the best evidence for efficacy comes from controlled trials in common cardiovascular and neurodegenerative diseases with mitochondrial and OXPHOS dysfunction the etiology of which is most likely multifactorial with environmental factors playing on a background of genetic predisposition. There remain questions about dosing, bioavailability, tissue penetration and intracellular distribution of orally administered CoQ10, a compound which is endogenously produced within the mitochondria of all cells. In some mitochondrial diseases and other commoner disorders such as cardiac disease and Parkinson's disease low mitochondrial or tissue levels of CoQ10 have been demonstrated providing an obvious rationale for supplementation. This paper discusses the current state of the evidence supporting the use of CoQ10 in mitochondrial disease.
Article
In mitochondria, most Coenzyme Q is free in the lipid bilayer; the question as to whether tightly bound, non-exchangeable Coenzyme Q molecules exist in mitochondrial complexes is still an open question. We review the mechanism of inter-complex electron transfer mediated by ubiquinone and discuss the kinetic consequences of the supramolecular organization of the respiratory complexes (randomly dispersed vs. super-complexes) in terms of Coenzyme Q pool behavior vs. metabolic channeling, respectively, both in physiological and in some pathological conditions. As an example of intra-complex electron transfer, we discuss in particular Complex I, a topic that is still under active investigation.
Article
The etiology of several neurodegenerative disorders is thought to involve impaired mitochondrial function and oxidative stress. Coenzyme Q-10 (CoQ10) acts both as an antioxidant and as an electron acceptor at the level of the mitochondria. In several animal models of neurodegenerative diseases including amyotrophic lateral sclerosis, Huntington's disease, and Parkinson's disease, CoQ10 has shown beneficial effects. Based on its biochemical properties and the effects in animal models, several clinical trials evaluating CoQ10 have been undertaken in many neurodegenerative diseases. CoQ10 appears to be safe and well tolerated, and several efficacy trials are planned.
Article
The plasma membrane of eukaryotic cells is the limit to interact with the environment. This position implies receiving stress signals that affects its components such as phospholipids. Inserted inside these components is coenzyme Q that is a redox compound acting as antioxidant. Coenzyme Q is reduced by diverse dehydrogenase enzymes mainly NADH-cytochrome b(5) reductase and NAD(P)H:quinone reductase 1. Reduced coenzyme Q can prevent lipid peroxidation chain reaction by itself or by reducing other antioxidants such as alpha-tocopherol and ascorbate. The group formed by antioxidants and the enzymes able to reduce coenzyme Q constitutes a plasma membrane redox system that is regulated by conditions that induce oxidative stress. Growth factor removal, ethidium bromide-induced rho degrees cells, and vitamin E deficiency are some of the conditions where both coenzyme Q and its reductases are increased in the plasma membrane. This antioxidant system in the plasma membrane has been observed to participate in the healthy aging induced by calorie restriction. Furthermore, coenzyme Q regulates the release of ceramide from sphingomyelin, which is concentrated in the plasma membrane. This results from the non-competitive inhibition of the neutral sphingomyelinase by coenzyme Q particularly by its reduced form. Coenzyme Q in the plasma membrane is then the center of a complex antioxidant system preventing the accumulation of oxidative damage and regulating the externally initiated ceramide signaling pathway.
Article
Statins are drugs of known and undisputed efficacy in the treatment of hypercholesterolemia, usually well tolerated by most patients. In some cases treatment with statins produces skeletal muscle complaints, and/or mild serum CK elevation; the incidence of rhabdomyolysis is very low. As a result of the common biosynthetic pathway Coenzyme Q (ubiquinone) and dolichol levels are also affected, to a certain degree, by the treatment with these HMG-CoA reductase inhibitors. Plasma levels of CoQ10 are lowered in the course of statin treatment. This could be related to the fact that statins lower plasma LDL levels, and CoQ10 is mainly transported by LDL, but a decrease is also found in platelets and in lymphocytes of statin treated patients, therefore it could truly depend on inhibition of CoQ10 synthesis. There are also some indications that statin treatment affects muscle ubiquinone levels, although it is not yet clear to which extent this depends on some effect on mitochondrial biogenesis. Some papers indicate that CoQ10 depletion during statin therapy might be associated with subclinical cardiomyopathy and this situation is reversed upon CoQ10 treatment. We can reasonably hypothesize that in some conditions where other CoQ10 depleting situations exist treatment with statins may seriously impair plasma and possible tissue levels of coenzyme Q10. While waiting for a large scale clinical trial where patients treated with statins are also monitored for their CoQ10 status, with a group also being given CoQ10, physicians should be aware of this drug-nutrient interaction and be vigilant to the possibility that statin drugs may, in some cases, impair skeletal muscle and myocardial bioenergetics.
Article
Plasma coenzyme Q10 (CoQ10) response to oral ingestion of various CoQ10 formulations was examined. Both total plasma CoQ10 and net increase over baseline CoQ10 concentrations show a gradual increase with increasing doses of CoQ10. Plasma CoQ10 concentrations plateau at a dose of 2400 mg using one specific chewable tablet formulation. The efficiency of absorption decreases as the dose increases. About 95% of circulating CoQ10 occurs as ubiquinol, with no appreciable change in the ratio following CoQ10 ingestion. Higher plasma CoQ10 concentrations are necessary to facilitate uptake by peripheral tissues and also the brain. Solubilized formulations of CoQ10 (both ubiquinone and ubiquinol) have superior bioavailability as evidenced by their enhanced plasma CoQ10 responses.
Article
A number of functions for coenzyme Q (CoQ) have been established during the years but its role as an effective antioxidant of the cellular membranes remains of dominating interest. This compound is our only endogenously synthesized lipid soluble antioxidant, present in all membranes and exceeding both in amount and efficiency that of other antioxidants. The protective effect is extended to lipids, proteins and DNA mainly because of its close localization to the oxidative events and the effective regeneration by continuous reduction at all locations. Its biosynthesis is influenced by nuclear receptors which may give the possibility, in the future, by using agonists or antagonists, of reestablishing the normal level in deficiencies caused by genetic mutations, aging or cardiomyopathy. An increase in CoQ concentration in specific cellular compartments in the presence of various types of oxidative stress appears to be of considerable interest.
Article
Details of the discovery of ubiquinone (coenzyme Q) are described in the context of research on mitochondria in the early 1950s. The importance of the research environment created by David E. Green to the recognition of the compound and its role in mitochondria is emphasized as well as the dedicated work of Karl Folkers to find the medical and nutritional significance. The development of diverse functions of the quinone from electron carrier and proton carrier in mitochondria to proton transport in other membranes and uncoupling protein control as well as antioxidant and prooxidant functions is introduced. The successful application in medicine points the way for future development.
Article
This review describes recent advances in our understanding of the uptake and distribution of coenzyme Q10 (CoQ10) in cells, animals, and humans. These advances have provided evidence of important pharmacokinetic factors, such as non-linear absorption and enterohepatic recirculation, and may facilitate the development of new CoQ10 formulations. Studies providing data which support the claim of tissue uptake of exogenous CoQ10 are also discussed. Improved CoQ10 dosing and drug level monitoring guidelines are suggested for adult and pediatric patient populations. Future CoQ10 research should consider uptake and distribution factors to determine cost-benefit relationships.
Article
Coenzyme Q10 (CoQ10) plays a pivotal role in oxidative phosphorylation (OXPHOS) as it distributes electrons between the various dehydrogenases and the cytochrome segments of the respiratory chain. Primary coenzyme Q10 deficiency is a rare, but possibly treatable, autosomal recessive condition with four major clinical presentations, an encephalomyopathic form, a generalized infantile variant with severe encephalopathy and renal disease, a myopathic form and an ataxic form. The diagnosis of ubiquinone deficiency is supported by respiratory chain analysis and eventually by the quantification of CoQ10 in patient tissues. We review here the infantile and pediatric quinone deficiency diseases as well as the clinical improvement after oral CoQ10 therapy. The clinical heterogeneity of ubiquinone deficiency is suggestive of a genetic heterogeneity that should be related to the large number of enzymes, and corresponding genes, involved in ubiquinone biosynthesis.
Article
Mevalonic aciduria (MVA) and phenylketonuria (PKU) are inborn errors of metabolism caused by deficiencies in the enzymes mevalonate kinase and phenylalanine 4-hydroxylase, respectively. Despite numerous studies the factors responsible for the pathogenicity of these disorders remain to be fully characterised. In common with MVA, a deficit in coenzyme Q10 (CoQ10) concentration has been implicated in the pathophysiology of PKU. In MVA the decrease in CoQ10 concentration may be attributed to a deficiency in mevalonate kinase, an enzyme common to both CoQ10 and cholesterol synthesis. However, although dietary sources of cholesterol cannot be excluded, the low/normal cholesterol levels in MVA patients suggests that some other factor may also be contributing to the decrease in CoQ10.The main factor associated with the low CoQ10 level of PKU patients is purported to be the elevated phenylalanine level. Phenylalanine has been shown to inhibit the activities of both 3-hydroxy-3-methylglutaryl-CoA reductase and mevalonate-5-pyrophosphate decarboxylase, enzymes common to both cholesterol and CoQ10 biosynthesis. Although evidence of a lowered plasma/serum CoQ10 level has been reported in MVA and PKU, few studies have assessed the intracellular CoQ10 concentration of patients. Plasma/serum CoQ10 is influenced by dietary intake as well as its lipoprotein content and therefore may be limited as a means of assessing intracellular CoQ10 concentration. Whether the pathogenesis of MVA and PKU are related to a loss of CoQ10 has yet to be established and further studies are required to assess the intracellular CoQ10 concentration of patients before this relationship can be confirmed or refuted.
Article
Coenzyme Q10 is administered for an ever-widening range of disorders, therefore it is timely to illustrate the latest findings with special emphasis on areas in which this therapeutic approach is completely new. These findings also give further insight into the biochemical mechanisms underlying clinical involvement of coenzyme Q10. Cardiovascular properties of coenzyme Q10 have been further addressed, namely regarding myocardial protection during cardiac surgery, end-stage heart failure, pediatric cardiomyopathy and in cardiopulmonary resuscitation. The vascular aspects of coenzyme Q10 addressing the important field of endothelial function are briefly examined. The controversial issue of the statin/coenzyme Q10 relationship has been investigated in preliminary studies in which the two substances were administered simultaneously. Work on different neurological diseases, involving mitochondrial dysfunction and oxidative stress, highlights some of the neuroprotective mechanisms of coenzyme Q10. A 4-year follow-up on 10 Friedreich's Ataxia patients treated with coenzyme Q10 and vitamin E showed a substantial improvement in cardiac and skeletal muscle bioenergetics and heart function. Mitochondrial dysfunction likely plays a role in the pathophysiology of migraine as well as age-related macular degeneration and a therapy including coenzyme Q10 produced significant improvement. Finally, the effect of coenzyme Q10 was evaluated in the treatment of asthenozoospermia. The latest findings highlight the beneficial role of coenzyme Q10 as coadjuvant in the treatment of syndromes, characterized by impaired mitochondrial bioenergetics and increased oxidative stress, which have a high social impact. Besides their clinical significance, these data give further insight into the biochemical mechanisms of coenzyme Q10 activity.
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It is proposed that ischemic preconditioning (PC) initiates signaling that converges on mitochondria and results in cardioprotection. The outcome of this signaling on mitochondrial enzyme complexes is yet to be understood. We therefore used proteomic methods to test the hypothesis that PC and pharmacological preconditioning similarly alter mitochondrial signaling complexes. Langendorff-perfused murine hearts were treated with the specific GSK-3 inhibitor AR-A014418 (GSK Inhib VIII) for 10 min or subjected to four cycles of 5-min ischemia-reperfusion (PC) before 20-min global ischemia and 120-min reperfusion. PC and GSK Inhib VIII both improved recovery of postischemic left ventricular developed pressure, decreased infarct size, and reduced lactate production during ischemia compared with their time-matched controls. We used proteomics to examine mitochondrial protein levels/posttranslational modifications that were common between PC and GSK Inhib VIII. Levels of cytochrome-c oxidase subunits Va and VIb, ATP synthase-coupling factor 6, and cytochrome b-c1 complex subunit 6 were increased while cytochrome c was decreased with PC and GSK Inhib VIII. Furthermore, the amount of cytochrome-c oxidase subunit VIb was found to be increased in PC and GSK Inhib VIII mitochondrial supercomplexes, which are comprised of complexes I, III, and IV. This result would suggest that changes in complex subunits associated with cardioprotection may affect supercomplex composition. Thus the ability of PC and GSK inhibition to alter the expression levels of electron transport complexes will have important implications for mitochondrial function.
Article
The role of reactive oxygen species (ROS) in cancer cells has been intensively studied for the past two decades. Cancer cells mostly have higher basal ROS levels than their normal counterparts. The induction of ROS has been shown to be associated with cancer development, metastasis, progression, and survival. Various therapeutic approaches targeting intracellular ROS levels have yielded mixed results. As widely accepted dietary supplements, antioxidants demonstrate both ROS scavenging ability and anti-cancer characteristics. However, antioxidants may not always be safe to use since excessive intake of antioxidants could lead to serious health concerns. In this review, we have evaluated the production and scavenging systems of ROS in cells, as well as the beneficial and harmful roles of ROS in cancer cells. We also examine the effect of antioxidants in cancer treatment, the effect of combined treatment of antioxidants with traditional cancer therapies, and the side effects of excessive antioxidant intake. Copyright © 2015. Published by Elsevier Ireland Ltd.
Article
The fundamental role of coenzyme Q(10) (CoQ(10)) in mitochondrial bioenergetics and its well-acknowledged antioxidant properties constitute the basis for its clinical applications, although some of its effects may be related to a gene induction mechanism. Cardiovascular disease is still the main field of study and the latest findings confirm a role of CoQ(10) in improving endothelial function. The possible relation between CoQ(10) deficiency and statin side effects is highly debated, particularly the key issue of whether CoQ(10) supplementation counteracts statin myalgias. Furthermore, in cardiac patients, plasma CoQ(10) was found to be an independent predictor of mortality. Studies on CoQ(10) and physical exercise have confirmed its effect in improving subjective fatigue sensation and physical performance and in opposing exercise-related damage. In the field of mitochondrial myopathies, primary CoQ(10) deficiencies have been identified, involving different genes of the CoQ(10) biosynthetic pathway; some of these conditions were found to be highly responsive to CoQ(10) administration. The initial observations of CoQ(10) effects in Parkinson's and Huntington's diseases have been extended to Friedreich's ataxia, where CoQ(10) and other quinones have been tested. CoQ(10) is presently being used in a large phase III trial in Parkinson's disease. CoQ(10) has been found to improve sperm count and motility on asthenozoospermia. Moreover, for the first time CoQ(10) was found to decrease the incidence of preeclampsia in pregnancy. The ability of CoQ(10) to mitigate headache symptoms in adults was also verified in pediatric and adolescent populations.
Article
Using cyclic voltammetry, we examined the dependence of the reduction potentials of six quinones on the concentration of the supporting electrolyte. An increase in the electrolyte concentration, resulting in an increase in the solution polarity, caused positive shifts of the reduction potentials. We ascribed the observed changes in the potentials to the dependence of the solvation energy of the quinones and their anions on the media polarity. Analysis of the reduction potentials, using the Born solvation energy equation, yielded unfeasibly small values for the effective radii of the quinone species, that is, the experimentally obtained effective radii were up to 4-fold smaller than the radii of the solvation cavities that we calculated for the quinones. The nonspherical shapes of the quinones, along with the uneven charge density distribution in their anions, encompassed the underlying reasons for the discrepancies between the obtained experimental and theoretical values for the radii of these redox species. The generalized Born approach, which does not treat the solvated species as single spheres, provided means for addressing this discrepancy and yielded effective radii that were relatively close to the measured values.
Book
This book focuses on the use of various molecules with antioxidant properties in the treatment of major male genital tract disorders, especially male infertility, erectile dysfunction, and accessory gland infection. The coverage also includes discussion of pathophysiology, the molecular basis of male infertility, and the rationale for use of antioxidants, with particular attention to coenzyme Q10 and carnitine. Oxidative stress occurs when the production of reactive oxygen species, including free radicals, exceeds the body’s natural antioxidant defences, leading to cellular damage. Oxidative stress is present in about half of all infertile men, and reactive oxygen species can produce infertility both by damaging the sperm membrane, with consequences for sperm motility, and by altering the sperm DNA. There is consequently a clear rationale for the use of antioxidant treatments within andrology, and various in vitro and in vivo studies have indicated that many antioxidants indeed have beneficial impacts. In providing a detailed and up-to-date overview of the subject, this book will be of interest to both practitioners and researchers in andrology, endocrinology, and urology.
Article
Nonalcoholic fatty liver disease (NAFLD) is currently the most common liver disease in the world. It encompasses a histological spectrum, ranging from simple, nonprogressive steatosis to nonalcoholic steatohepatitis (NASH), which may progress to cirrhosis and hepatocellular carcinoma. While liver-related complications are confined to NASH, emerging evidence suggests both simple steatosis and NASH predispose to type 2 diabetes and cardiovascular disease. The pathogenesis of NAFLD is currently unknown, but accumulating data suggest that oxidative stress and altered redox balance play a crucial role in the pathogenesis of steatosis, steatohepatitis, and fibrosis. We will examine intracellular mechanisms, including mitochondrial dysfunction and impaired oxidative free fatty acid metabolism, leading to reactive oxygen species generation; additionally, the potential pathogenetic role of extracellular sources of reactive oxygen species in NAFLD, including increased myeloperoxidase activity and oxidized low density lipoprotein accumulation, will be reviewed. We will discuss how these mechanisms converge to determine the whole pathophysiological spectrum of NAFLD, including hepatocyte triglyceride accumulation, hepatocyte apoptosis, hepatic inflammation, hepatic stellate cell activation, and fibrogenesis. Finally, available animal and human data on treatment opportunities with older and newer antioxidant will be presented.
Article
A high-fat diet affects liver metabolism, leading to steatosis, a complex disorder related to insulin resistance and mitochondrial alterations. Steatosis is still poorly understood since diverse effects have been reported, depending on the different experimental models used. We hereby report the effects of an 8 week high-fat diet on liver energy metabolism in a rat model, investigated in both isolated mitochondria and hepatocytes. Liver mass was unchanged but lipid content and composition were markedly affected. State-3 mitochondrial oxidative phosphorylation was inhibited, contrasting with unaffected cytochrome content. Oxidative phosphorylation stoichiometry was unaffected, as were ATPase and adenine nucleotide translocator proteins and mRNAs. Mitochondrial acylcarnitine-related H(2)O(2) production was substantially higher and the mitochondrial quinone pool was smaller and more reduced. Cellular consequences of these mitochondrial alterations were investigated in perifused, freshly isolated hepatocytes. Ketogenesis and fatty acid-dependent respiration were lower, indicating a lower β-oxidation rate contrasting with higher RNA contents of CD36, FABP, CPT-1, and AcylCoA dehydrogenases. Concomitantly, the cellular redox state was more reduced in the mitochondrial matrix but more oxidized in the cytosol: these opposing changes are in agreement with a significantly higher in situ mitochondrial proton motive force. A high-fat diet results in both a decrease in mitochondrial quinone pool and a profound modification in mitochondrial lipid composition. These changes appear to play a key role in the resulting inhibition of fatty acid oxidation and of mitochondrial oxidative-phosphorylation associated with an increased mitochondrial ROS production. Mitochondrial quinone pool could have prospects as a crucial event, potentially leading to interesting therapeutic perspectives.
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For a number of years, coenzyme Q (CoQ10 in humans), was known for its key role in mitochondrial bioenergetics; later studies demonstrated its presence in other subcellular fractions and in plasma, and also extensively investigated its antioxidant role. This chapter discusses the relationship between the acknowledged bioenergetic role of CoQ10 and some clinical effects. The antioxidant properties of CoQ10 are then analyzed especially for their consequences on protection of circulating human low-density lipoproteins and prevention of atherogenesis. The relationship between CoQ10 and statins is also discussed in the light of possible involvement of CoQ10 deficiency in the issue of statin side effects. New aspects of the antioxidant involvement of coenzyme Q are also discussed together with their relevance in cardiovascular disease. Data are reported on the efficacy of CoQ10 in ameliorating endothelial dysfunction in patients affected by ischemic heart disease. Many of the effects of CoQ10, which were classically ascribed to its bioenergetic properties, are now considered as the result of its biochemical interaction with nitric oxide (NO), NO synthase and reactive oxygen species capable of inactivating NO. Clinical studies are reported highlighting the effect of CoQ10 on extracellular SOD, which is deeply involved in endothelial dysfunction. Previous studies have shown decreased levels of CoQ10 in the seminal plasma and sperm cells of infertile men with different kinds of asthenospermia. Research has been extended to supplementation with CoQ10 of infertile men affected by idiopathic asthenozoospermia. CoQ10 levels increased significantly in seminal plasma and sperm cells after 6 months of treatment with concomitant improvement of sperm cell motility.
Chapter
The function of proteins is dependent on other proteins. Proteins function as oligomers, complexes, super-complexes or higher order networks, in which they interact with each other, either temporarily when they exert their function or ‘permanently’ in functional units. Genetic defects in single proteins may therefore, in addition to disturbing the specific function of the defective protein, disturb other functions that are dependent on it. In this review we will discuss how the two main types of defects in genetic disease, truncating variations (stop-codon introductions and small out-of-frame deletions/insertions) and in-frame variations (missense variations and small in-frame deletions/insertions), may disturb normal interactions. Depending on the importance (location) of the missing or aberrant protein, the effect on the cellular pathway or interacting network may be severe or mild. Protein interactions and disturbances therein may be determined by protein mass spectrometry after immuno-precipitation or other fractionation and separation methods.
Article
An excessive production of oxidants disturbs the normal intracellular equilibrium, and can lead to an “oxidative stress”. Recent data indicate that several components of the regular diet as well as chemical compounds and drugs can modulate the so-called “oxidative stress” both via anti-oxidant effects and via inhibition or activation of the enzymes involved in reactive nitrogen oxygen species (RNOS). We will describe in this review article the biochemistry of oxygen, the physiological roles and regulation of oxidative stress. The clinical relevance of uncontrolled oxidative stress will be presented as well as the results of therapeutic trials with antioxidants. New promising strategies which modulate the activities of the RNOS generating enzymes, with selected catalytic inhibitors will be discussed.
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The mitochondria are essential for normal cell functioning. Changes in mitochondrial DNA (mtDNA) may affect the occurrence of some chronic diseases and cancer. This process is complex and not entirely understood. The assignment to a particular mitochondrial haplogroup may be a factor that either contributes to cancer development or reduces its likelihood. Mutations in mtDNA occurring via an increase in reactive oxygen species may favour the occurrence of further changes both in mitochondrial and nuclear DNA. Mitochondrial DNA mutations in postmitotic cells are not inherited, but may play a role both in initiation and progression of cancer. One of the first discovered polymorphisms associated with cancer was in the gene NADH-ubiquinone oxidoreductase chain 3 (mt-ND3) and it was typical of haplogroup N. In prostate cancer, these mutations and polymorphisms involve a gene encoding subunit I of respiratory complex IV cytochrome c oxidase subunit 1 gene (COI). At present, a growing number of studies also address the impact of mtDNA polymorphisms on prognosis in cancer patients. Some of the mitochondrial DNA polymorphisms occur in both chronic disease and cancer, for instance polymorphism G5913A characteristic of prostate cancer and hypertension.
Chapter
Human coenzyme Q (CoQ10) or ubiquinone is mainly known for its bioenergetic role as a proton and electron carrier in the inner mitochondrial membrane and is also an endogenous lipophilic antioxidant, ubiquitous in biological membranes. It is also present in plasma lipoproteins, where it plays a well-recognized antioxidant role. More recently coenzyme Q10 was also shown to affect gene expression by modulating the intracellular redox status. Its involvement in many cellular and extracellular functions suggests that its use as a food supplement could be beneficial in conditions associated with increased oxidative stress underlying different pathological conditions. In reproductive biology, CoQ10 has been shown to play a role in fertility of both males and females.
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Eccentric exercise (EE) is known to induce damage and dysfunction in skeletal muscle. However, the possible role of mitochondrial (dys)function, including the vulnerability to mitochondrial permeability transition pore (MPTP) opening, is unclear. Therefore, this study aimed to analyze the impact of a single acute bout of downhill running on skeletal muscle mitochondrial function. Thirty 12-week-old Charles River CD1 male mice were randomly assigned into control (C) or exercised groups. EE consisted of 120 min of downhill treadmill running at a -16° gradient. Exercised animals were sacrificed immediately (Ecc0h) and 48 h (Ecc48h) after the end of the running bout. Plasma and skeletal muscles were then obtained. Muscle mitochondrial function, including oxygen consumption prior to and after anoxia and reoxygenation, membrane potential, and MPTP opening, were evaluated. Respiratory chain complexI, II, and V activities were determined. EE significantly increased plasma creatine kinase activity (119.4 ± 5.6 vs. 1061.3 ± 46.3 vs. 256.8 ± 15.3 U·L(-1), C, Ecc0h and Ecc48h, respectively) and myoglobin and interleukin-6 content. Impaired state 3 and respiratory control ratio (8.4 ± 0.4 vs. 5.6 ± 0.9 vs. 8.4 ± 0.5, C, Ecc0h and Ecc48h, respectively), as well as increased susceptibility to MPTP opening, seen by cyclosporin A-sensitive high swelling amplitude, lower time to maximal swelling velocity (313.8 ± 17.7 vs. 244.5 ± 19.4 vs. 298.5 ± 8.7 s, C, Ecc0h and Ecc48h, respectively), and calcium release immediately after the end of exercise (C vs. Ecc0h) were observed. EE induced a transient impairment in the activity of complex V (C vs. Ecc0h). No significant changes from the C group were observed 48 h after the end of EE (C vs. Ecc48h) in any analyzed parameters. In conclusion, prolonged EE transiently impaired mice skeletal muscle mitochondrial function and increased susceptibility to calcium-induced MPTP opening.
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Mitochondria provide the main source of energy to eukaryotic cells, oxidizing fats and sugars to generate adenosine 5'-triphosphate (ATP). Mitochondrial fatty acid β-oxidation (FAO) and oxidative phosphorylation (OXPHOS) are two metabolic pathways which are central to this process. Defects in these pathways can result in diseases of the brain, skeletal muscle, heart and liver, affecting approximately 1 in 5,000 live births. There are no effective therapies for these disorders, with quality of life severely reduced for most patients. The pathology underlying many aspects of these diseases is not well understood; for example, it is not clear why some patients with primary FAO deficiencies exhibit secondary OXPHOS defects. However, recent findings suggest that physical interactions exist between FAO and OXPHOS proteins, and that these interactions are critical for both FAO and OXPHOS function. Here, we review our current understanding of the interactions between FAO and OXPHOS proteins and how defects in these two metabolic pathways contribute to mitochondrial disease pathogenesis.
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The regular practice of physical activity is recommended usually with the aim to control the development of degenerative deseases. However, studies on oxidative stress demonstrated that the increase in the rate of oxygen consumption (O2) in the cell could, in parallel, to favor the occurrence of oxidative damage in biomolecules. In the case of the athletic training, those lesions might assume larger dimensions. Oxidative stress refer to the unbalance occurred in the organism in favor of superoxide (O2 •-), hydrogen peroxide (H2O2) and hydroxil radical (•OH) formation, among others, denominated reactive oxygen species (ROS), comparative to the chemical (vitamin C, E, carotene, phenols, etc.) and enzymatic (superoxide dismutase, catalase, glutathione peroxidase, etc.) antioxidants available. Those oxygen derived chemical species are responsible for the oxidative stress provoked by the intense physical exercise, being •OH the more harmful chemical specie recognized. Therefore, in spite that physical activity is frequently related with fitness, some sided effects provoked by the intense physical activity might result in negative alterations of cellular functionality. Among the oxidative damage in biomolecules provoked by ROS, lipid peroxidation is the more studied. We intended in this work, to review the data available on this subject.
Article
Since the identification of the genetic mutation causing Friedreich's ataxia (FRDA) our understanding of the mechanisms underlying disease pathogenesis have improved markedly. The genetic abnormality results in the deficiency of frataxin, a protein targeted to the mitochondrion. There is extensive evidence that mitochondrial respiratory chain dysfunction, oxidative damage and iron accumulation play significant roles in the disease mechanism. There remains considerable debate as to the normal function of frataxin, but it is likely to be involved in mitochondrial iron handling, antioxidant regulation, and/or iron sulphur centre regulation. Therapeutic avenues for patients with FRDA are beginning to be explored in particular targeting antioxidant protection, enhancement of mitochondrial oxidative phosphorylation, iron chelation and more recently increasing FRDA transcription. The use of quinone therapy has been the most extensively studied to date with clear benefits demonstrated using evaluations of both disease biomarkers and clinical symptoms, and this is the topic that will be covered in this review.
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The knowledge of coenzyme Q levels in tissues, organs, and subcellular compartments is of outstanding interest. A wide amount of data regarding coenzyme Q distribution and occurrence was collected in the last decades; nevertheless the data are often hard to compare because of the different extraction methods and different analytical techniques used. We have undertaken a systematic study for detecting the ubiquinone content in subcellular compartments, cells, and whole-tissue homogenates by a previously standardized HPLC method performed after an extraction procedure identical for all samples. It was confirmed that the major coenzyme Q homologue in rat tissues is coenzyme Q9; however, it was pointed out that all the rodents samples tested contain more than one coenzyme Q homologue. The coenzyme Q homologue distribution is tissue dependent with relatively high coenzyme Q10 content in brain mitochondria, irrespective of the rat strain used. There is no constant relationship of the coenzyme Q content in mitochondria and microsomes fractions. Most organisms tested (including other mammals, bird and fish specimens) have only coenzyme Q10, while the protozoan Tetrahymena pyriformis contains only coenzyme Q8.
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Evidence for the presence of a quinol oxidase super-complex composed of a cytochrome bc1 complex and cytochrome oxidase in the respiratory chain of a Gram-positive thermophilic bacterium PS3 is reported. On incubation with an octyl glucoside-solubilized fraction of the total membranes of PS3 anti-serum against PS3 cytochrome oxidase gave an immunoprecipitate that showed both quinol-cytochrome c reductase and cytochrome c oxidase activities. When the cholate-deoxycholate and LiCl-treated membranes of PS3 were solubilized and subjected to ion-exchange chromatography in the presence of octaethyleneglycol dodecyl ether, most of the A-, B-, and C-type cytochromes were copurified as a peak having both quinol-cytochrome c reductase and cytochrome oxidase activities. The immunoprecipitate and quinol oxidase preparation contained hemes a, b, and c in a ratio of about 2:2:3, indicating the presence of one-to-one complex of cytochrome oxidase containing 2 hemes a and one heme c, and a bc1 complex containing 2 hemes b and 2 hemes c. Gel electrophoresis in the presence of dodecyl sulfate showed that the immunoprecipitate and quinol oxidase preparation were composed of seven subunits; those of 51 (56-kDa), 38, and 22 kDa for cytochrome oxidase and those of 29, 23, 21, and 14 kDa for the bc1 complex. The 38-, 29-, and 21 kDa components possessed covalently bound heme c. The apparent molecular mass of the super complex was estimated to be as 380 kDa by gel filtration.
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We have compared the modes and rates of cytochrome c diffusion to the rates of cytochrome c-mediated electron transport in isolated inner membranes and in whole intact mitochondria. For inner membranes, an increasing ionic strength results in an increasing rate of cytochrome c diffusion, a decreasing concentration (affinity) of cytochrome c near the membrane surface as well as near its redox partners, and an increasing rate of electron transport. For intact mitochondria, an increasing ionic strength results in a parallel, increasing rate of cytochrome c-mediated electron transport. In both inner membranes and intact mitochondria the rate of cytochrome c-mediated electron transport is highest at physiological ionic strength (100-150 mM), where the diffusion rate of cytochrome c is highest and its diffusion mode is three-dimensional. In intact mitochondria, succinate and duroquinol-driven reduction of endogenous cytochrome c is greater than 95% at all ionic strengths, indicating that cytochrome c functions as a common pool irrespective of its diffusion mode. Using a new treatment to obtain bimolecular diffusion-controlled collision frequencies in a heterogenous diffusion system, where cytochrome c diffuses laterally, pseudo-laterally, or three-dimensionally while its redox partners diffuse laterally, we determined a high degree of collision efficiency (turnover/collisions) for cytochrome c with its redox partners for all diffusion modes of cytochrome c. At physiological ionic strength, the rapid diffusion of cytochrome c in three dimensions and its low concentration (affinity) near the surface of the inner membrane mediate the highest rate of electron transport through maximum collision efficiencies. These data reveal that the diffusion rate and concentration of cytochrome c near the surface of the inner membrane are rate-limiting for maximal (uncoupled) electron transport activity, approaching diffusion control.
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We have determined the modes and rates of cytochrome c diffusion as well as the collision frequencies of cytochrome c with its redox partners at the surface of the isolated, mitochondrial inner membrane over a broad range (0-150 mM) of ionic strengths. Using fluorescence recovery after photobleaching, resonance energy transfer, and direct binding assay, we determined that the diffusion coefficient of cytochrome c is independent of its concentration and quantity bound to the inner membrane, that the distance of cytochrome c from the membrane surface increases with increasing ionic strength, and that there is no significant immobile fraction of cytochrome c on the membrane regardless of ionic strength. The rate of cytochrome c diffusion increases while its mode of diffusion changes progressively from lateral to three-dimensional with increasing ionic strength. At physiological ionic strength (100-150 mM), the diffusion of cytochrome c is three-dimensional with respect to the surface of the inner membrane with a coefficient of 1.0 x 10(-6) cm2/s, and little, if any cytochrome c is bound to the membrane regardless of its concentration. Furthermore, as ionic strength is raised from zero to 150 mM, the cytochrome ckd for the inner membrane increases, its mean occupancy time on the inner membrane to collide with a redox partner (tau) decreases, and its diffusion-based collision frequencies with its redox partners decrease. These data reveal the significance of both diffusion and concentration (affinity) of cytochrome c near the surface of the inner membrane in the control of the collision frequency of cytochrome c with its redox partners.
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The molecular structure of mitochondria and their inner membrane has been studied using a combined approach of stereology and biochemistry. The amount of mitochondrial structures (volume, number, surface area of inner membrane) in a purified preparation of mitochondria from rat liver was estimated by stereological procedures. In the same preparation, the oxidative activity of the respiratory chain with different substrates and the concentration of the redox complexes were measured by biochemical means. By relating the stereological and biochemical data, it was estimated that the individual mitochondrion isolated from rat liver has a volume of 0.27 micron 3, an inner membrane area of 6.5 micron 2, and contains between 2,600 (complex I) and 15,600 (aa3) redox complexes which produce an electron flow of over 100,000 electrons per second with pyruvate as substrate. The individual redox complexes and the H+-ATPase together occur at a density of approximately 7,500/micron 2 and occupy approximately 40% of the inner membrane area. From the respective densities it was concluded that the mean nearest distance between reaction partners is small enough (70-200 A) to cause the formation of micro-aggregates. The meaning of these results for the mechanism of mitochondrial energy transduction is discussed.
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An enzyme complex with ubiquinol-cytochrome c oxidoreductase, cytochrome c oxidase, and ubiquinol oxidase activities was purified from a detergent extract of the plasma membrane of aerobically grown Paracoccus denitrificans. This ubiquinol oxidase consists of seven polypeptides and contains two b cytochromes, cytochrome c1, cytochrome aa3, and a previously unreported c-type cytochrome. This c-type cytochrome has an apparent Mr of 22,000 and an alpha absorption maximum at 552 nm. Retention of this c cytochrome through purification presumably accounts for the independence of ubiquinol oxidase activity on added cytochrome c. Ubiquinol oxidase can be separated into a 3-subunit bc1 complex, a 3-subunit c-aa3 complex, and a 57-kDa polypeptide. This, together with detection of covalently bound heme and published molecular weights of cytochrome c1 and the subunits of cytochrome c oxidase, allows tentative identification of most of the subunits of ubiquinol oxidase with the prosthetic groups present. Ubiquinol oxidase contains cytochromes corresponding to those of the mitochondrial bc1 complex, cytochrome c oxidase complex, and a bound cytochrome c. Ubiquinol-cytochrome c oxidoreductase activity of the complex is inhibited by inhibitors of the mitochondrial bc1 complex. Thus it seems likely that the pathway of electron transfer through the bc1 complex of ubiquinol oxidase is similar to that through the mitochondrial bc1 complex. The number of polypeptides present is less than half the number in the corresponding mitochondrial complexes. This structural simplicity may make ubiquinol oxidase from P. denitrificans a useful system with which to study the mechanisms of electron transfer and energy transduction in the bc1 and cytochrome c oxidase sections of the respiratory chain.
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The interaction between 1,2-dipalmitoyl phosphatidylcholine and ubiquinone-10 in aqueous systems was studied by difference i.r. spectroscopy. Binary mixtures of the two lipids in proportions of 2, 5 and 15 mol% were investigated in the spectral regions reporting on the hydrocarbon chains of the phospholipid and the polar phosphate group. No spectral shifts or significant broadening of any absorbances due to the phospholipid were detected at temperatures of 20 or 54 degrees C. Changes in the frequency of the maximum of the CH2 antisymmetric C-H stretching vibration with temperature indicated that the gel-to-liquid-crystal-line phase-transition temperature of the phospholipid was lowered by about 2 degrees C in the presence of between 2 and 15 mol% ubiquinone-10. Absorbance by the benzoquinone substituent of ubiquinone-10 was detected by spectral subtraction of dispersions of phospholipid alone. Bands due to C = O stretching and ester group vibrations of ubiquinone-10 in co-dispersion with phospholipid were compared with the same spectral region when ubiquinone-10 was dissolved in solvents or as a crystalline solid. Spectral changes could be detected when ubiquinone-10 in phospholipid was compared with solution in dodecane and chloroform. These may indicate that the benzoquinone ring system is located within a hydrocarbon domain in dispersions with dipalmitoyl phosphatidylcholine. It was concluded from the study that when ubiquinone-10 is co-dispersed with dipalmitoyl phosphatidylcholine in water the two lipids phase-separate. There is no evidence that ubiquinone-10 intercalates between phospholipid molecules, which undergo a gel-liquid-crystalline phase transition in only a slightly modified form. The data suggest that the benzoquinone substituent resides in a hydrophobic domain and that aggregates spanning the bilayer are a possible arrangement of the ubiquinone in the structure.
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The cytochrome b-c1 complex has been “solubilized” and purified to a stage containing 6.5 nmoles of cytochrome b per mg of protein. Seven bands are resolved on a polyacrylamide gel electrophoretic column in sodium dodecyl sulfateβ-mercaptoethanol medium. Five of these seven bands have been identified as cytochromes b and c1 and a non-heme iron protein. The remaining two bands might be associated with these components or, less likely, might be impurities but do not belong to the so-called structural proteins. The cytochrome b-c1 complex is enzymatically active and can reconstitute with soluble succinate dehydrogenase to form an integral entity of antimycin A-sensitive succinate-cytochrome c reductase. The reconstituted reductase shows the same structural and functional characteristics as the intact reductase. The total number of the p-hydroxymercuribenzoate (p-MB) titratable groups in the cytochrome b-c1 complex has been found to be 11 ± 1 moles per mole of cytochrome b. The p-MB-reacted complex is inactive in reconstitution but shows the same catalytic activity in the oxidation of reduced ubiquinone by cytochrome c.
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This chapter discusses the constraints of the mitochondrial membrane in determining and regulating electron transfer function. It focuses on the heme-containing components of the inner mitochondrial membrane, namely, the cytochromes. These cytochromes provide interesting intrinsic chromophores suitable for optical probing in situ. It provides an overview on physical techniques, which determine orientation, distances, structure, and motion of the electron carriers. It is generally accepted that the respiratory chain components undergo independent diffusion. The rotational and transverse motions of cytochrome c oxidase and cytochrome c are directly measured. The rotational motion of the ADP/ATP translocator has been established and the transverse diffusion of the cytochrome bc1 complex has been demonstrated. The chapter also explains that specificity is achieved by having specific interaction domains on the electron carrier for its redox partners. In this regard, much work has been done on cytochrome c to explain its interaction domains with the oxidase and the reductase
Chapter
This past year has seen such a plethora of reviews and “mini-reviews” on the mechanism of oxidative phosphorylation (e.g., refs. 1–3) that it would be both tedious and arrogant of me to add to their number. Instead, I propose to offer some personal thoughts on the subject, illustrated by reference to some of our own work, past and present. This selection is not intended to claim any particular priorities; indeed, in some cases the examples are more of pitfalls than of positive contributions. The common thread is that when the contributions have proved to be useful they have been based on the solid conceptual framework of the organization of the inner mitochondrial membrane in general and of the respiratory chain in particular, which is one of the great contributions that David Green has made to science.
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Affinity purified immunoglobulin of the IgG class, monospecific for cytochrome c oxidase, and the ferritin conjugate of the IgG, were used as membrane impermeable probes for the purpose of determining the orientation and spatial, site by site distribution of functional cytochrome c oxidase on the two surfaces of the inner mitochondrial membrane. Affinity purified IgG was prepared using bovine heart cytochrome c oxidase as the immunosorbent and proved to be monospecific for the bovine heart enzyme as well as for cytochrome c oxidase of detergent solubilized rat liver mitochondria. The IgG inhibited succinate oxidase and ascorbate cytochrome c oxidase activity immediately and completely when reacted with (a) a purified, metabolically and structurally intact inner membrane matrix fraction prepared from rat liver mitochondria and (b) an inverted inner membrane vesicle preparation produced from the inner membrane matrix fraction. In direct contrast, IgG monospecific for cytochrome c inhibited succinate oxidase activity immediately and completely in the inner membrane matrix fraction but showed no inhibitory effect on the inverted inner membrane vesicle preparation. Analysis of ferricyanide reduction and difference spectra of the inner membrane bound heme proteins revealed that both immunoglobulins, those monospecific for cytochrome c oxidase and for cytochrome c, completely displaced cytochrome c from the surface of the inner membrane matrix fraction. Neither immunoglobulin affected electron transport in mitochondria possessing an intact outer membrane. The data reveal: (a) AU cytochrome c oxidase which is active during the oxidation of succinate and ascorbate is accessible on both surfaces of the inner membrane through a transmembrane orientation; no cytochrome c oxidase functional in electron transport is restricted to only one surface of the membrane. (b) AU cytochrome a which catalyzes the oxidation of ferrocytochrome c is restricted in its orientation to the outer surface of the inner membrane while all cytochrome a 3 which catalyzes the reduction of oxygen is restricted in its orientation to the inner surface of the inner membrane. (c) Approximately 2000 cytochrome c oxidase binding sites are available through immunodeterminants of the oxidase on the outer surface of the intact inner membrane in a relatively disordered spatial distribution over both the cristal and inner boundary membrane regions.
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This chapter describes the preparative procedures and properties of the subchloroplast fragments. Digitonin, a nonionic detergent, disrupts chloroplasts into fragments with different pigment compositions and with different photochemical activities. The larger fragments are enriched in photosystem II, whereas the smaller fragments have the properties of photosystem I. Therefore, incubation of chloroplasts with digitonin produces a physical separation of the photochemical systems. Chloroplasts are prepared from spinach leaves (Spinacia oleracea L.) and washed once with the sucrose–KCl–phosphate buffer. The subchloroplast fragments are separated by differential centrifugation. The first centrifugation is at 1000 g for 10 minutes in an SS-34 rotor of a Servall refrigerated centrifuge (RC-2). Subsequent centrifugations are at 10,000 g for 30 minutes in a Servall centrifuge, 50,000 g (23,000 rpm) for 30 minutes in a No. 40 rotor of a Spinco Model L centrifuge, and 144,000 g (40,000 rpm) for 60 minutes in a Spinco centrifuge. The pellets from each centrifugation are suspended in 50 mM phosphate buffer + 10 mM KCl and designated 1000 g (D-l), 10,000 g (D-10), 50,000 g (D-50), and 144,000 g (D-144) fractions. Brief sonication for seven seconds in a sonic disintegrator (10-kHz, 250-W Raytheon) facilitates resuspension. The volumes of resuspension buffer for fragments prepared from 8 g of leaves are D-l, 2 ml; D-10, 6 ml; D-50, 1.5 ml; and D-144, 1.5 ml.
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A project to systematically investigate respiratory supercomplexes in plant mitochondria was initiated. Mitochondrial fractions from Arabidopsis, potato (Solanum tuberosum), bean (Phaseolus vulgaris), and barley (Hordeum vulgare) were carefully treated with various concentrations of the nonionic detergents dodecylmaltoside, Triton X-100, or digitonin, and proteins were subsequently separated by (a) Blue-native polyacrylamide gel electrophoresis (PAGE), (b) two-dimensional Blue-native/sodium dodecyl sulfate-PAGE, and (c) two-dimensional Blue-native/Blue-native PAGE. Three high molecular mass complexes of 1,100, 1,500, and 3,000 kD are visible on one-dimensional Blue native gels, which were identified by separations on second gel dimensions and protein analyses by mass spectrometry. The 1,100-kD complex represents dimeric ATP synthase and is only stable under very low concentrations of detergents. In contrast, the 1,500-kD complex is stable at medium and even high concentrations of detergents and includes the complexes I and III2. Depending on the investigated organism, 50% to 90% of complex I forms part of this supercomplex if solubilized with digitonin. The 3,000-kD complex, which also includes the complexes I and III, is of low abundance and most likely has a III4I2 structure. The complexes IV, II, and the alternative oxidase were not part of supercomplexes under all conditions applied. Digitonin proved to be the ideal detergent for supercomplex stabilization and also allows optimal visualization of the complexes II and IV on Blue-native gels. Complex II unexpectedly was found to be composed of seven subunits, and complex IV is present in two different forms on the Blue-native gels, the larger of which comprises additional subunits including a 32-kD protein resembling COX VIb from other organisms. We speculate that supercomplex formation between the complexes I and III limits access of alternative oxidase to its substrate ubiquinol and possibly regulates alternative respiration. The data of this investigation are available at http://www.gartenbau.uni-hannover.de/genetik/braun/AMPP.
Article
The mitochondrial electron transport chain complexes are large multisubunit complexes embedded in the inner membrane. We report here that in the yeast Saccharomyces cerevisiae, the cytochrome bc 1 and cytochrome c oxidase complexes co-exist as a larger complex of ∼1000 kDa in the mitochondrial membrane. Following solubilization with a mild detergent, the cytochromebc 1-cytochrome c oxidase complex remains stable. It was analyzed using the techniques of gel filtration and blue native-polyacrylamide gel electrophoresis. Direct physical association of subunits of the cytochrome bc 1complex with those of the cytochrome c oxidase complex was verified by co-immunoprecipitation analysis. Our data indicate that the cytochrome bc 1 complex is exclusively in association with the cytochrome c oxidase complex in yeast mitochondria. We term this complex the cytochromebc 1-cytochrome c oxidase supracomplex.
Article
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Article
The role of ubiquinone (Q) in the respiratory chain is quantitatively analyzed by correlating both the steady-state redox level of Q and the kinetics of oxidation and reduction with the flux of the overall electron transport in uncoupled submitochondrial particles. This is achieved by experimentally defining donor and acceptor activities for Q.1The degree of reduction of Q in the steady state is proportional to the respiratory activity with NADH and succinate, if the respiratory activity is varied by titrating the donor side for Q with rotenone and malonate, respectively. The proportionality constant (acceptor activity, Vox) is independent of the substrate used.2The degree of oxidation of Q in the steady state is proportional to the respiratory activity as varied by titration of the acceptor side for Q with antimycin. The proportionality constant (donor activity, Vred) is independent of the acceptor activity and depends on the dehydrogenase activity for NADH and succinate.3From these experimental relations, the redox state of Q in the steady state and the respiratory activity can be described as functions of the donor and the acceptor activity only. The equations are valid with both NADH and succinate as the substrates.4The kinetics of oxidation of Q on the addition of oxygen as measured by the quench-flow method are in agreement with that measured by direct absorption recording in a mixing chamber. The reaction is first order with a rate constant equal to the acceptor activity divided by the amount of redox-active Q (Vox/Qa). The final steady-state level (in the present case 15% reduction) is a result also of the reduction reaction with the first-order rate constant, VredQa.5The acceptor activity can also be measured as maximum respiratory activity with duro-hydroquinone. This activity is independent of the presence of Q but sensitive to antimycin. Thus, the acceptor activity for ubiquinone can be measured by three independent methods.6It is concluded, that also in the steady state the reduction and oxidation of the active Q-pool follow pseudo-first-order reactions, the rates of which are equal to the respiratory rate. The total amount of redox-active Q is kinetically and functionally homogeneous and is not divided into substrate-specific compartments.
Article
An improved method was developed to sequentially fractionate succinate-cytochrome c reductase into three reconstitutive active enzyme systems with good yield: pure succinate dehydrogenase, ubiquinone-binding protein fraction and a highly purified ubiquinol-cytochrome c reductase (cytochrome b-c1 III complex).An extensively dialyzed succinate-cytochrome c reductase was first separated into a succinate dehydrogenase fraction and the cytochrome b-c1 complex by alkali treatment. The resulting succinate dehydrogenase fraction was further purified to homogeneity by the treatment of butanol, calcium phosphate gel adsorption and ammonium sulfate fractionation under anaerobic condition in the presence of succinate and dithiothreitol. The cytochrome b-c1 complex was separated into cytochrome b-c1 III complex and ubiquinone-binding protein fractions by careful ammonium acetate fractionation in the presence of deoxycholate.The purified succinate dehydrogenase contained only two polypeptides with molecular weights of 70 000 and 27 000 as revealed by the sodium dodecyl sulfate polyacrylamide gel electrophoretic pattern. The enzyme has the reconstitutive activity and a low Km ferricyanide reductase activity of 85 μmol succinate oxidized per min per mg protein at 38°C.Chemical composition analysis of cytochrome b-c1 III complex showed that the preparation was completely free of contamination of succinate dehydrogenase and ubiquinone-binding protein and was 30% more pure than the available preparation.When these three components were mixed in a proper ratio, a thenoyl-trifluoroacetone- and antimycin A-sensitive succinate-cytochrome c reductase was reconstituted.
Article
1. Beef heart mitochondria have a cytochrome c1:c:aa3 ratio of 0.65:1.0:1.0 as isolated; Keilin-Hartree submitochondrial particles ahve a ratio of 0.65:0.4:1.0. More than 50% of the submitochondrial particle membrane is in the 'inverted' configuration, shielding the catalytically active cytochrome c. The 'endogenous' cytochrome c of particles turns over at a maximal rate between 450 and 550 s-1 during the oxidation of succinate or ascorbate plus TMPD; the maximal turnover rate for cytochrome c in mitochondria is 300-400 s-1, at 28 degrees-30 degrees C, pH 7.4. 2. Ascorbate plus N,N,N',N'-tetramethyl-p-phenylene diamine added to antimycin-treated particles induces anomalous absorption increases between 555 and 565 nm during the aerobic steady state, which disappear upon anaerobiosis; succinate addition abolishes this cycle and permits the partial resolution of cytochrome c1 and cytochrome c steady states at 552.5-547 nm and 550-556.5 nm, respectively. 3. Cytochrome c1 is rather more reduced than cytochrome c during the oxidation of succinate and of ascorbate + N,N,N',N'-tetramethyl-p-phenylene diamine in both mitochondria and submitochondrial particles; a near equilibrium condition exists between cytochromes c1 and c in the aerobic steady state, with a rate constant for the c1 leads to c reduction step greater than 10(3) s-1. 4. The greater apparent response of the c/aa3 electron transfer step to salts, the hyperbolic inhibition of succinate oxidation by azide and cyanide, and the kinetic behaviour of the succinate-cytochrome c reductase system, are all explicable in terms of a near-equilibrium condition prevailing at the c1/c step. Endogenous cytochrome c of mitochondria and submitochondrial particles is apparently largely bound to cytochrome aa3 units in situ. Cytochrome c1 can either reduce the cytochrome c-cytochrome aa3 complex directly, or requires only a small extra amount of cytochrome c to carry the full electron transfer flux.
Article
Cytochrome c oxidase depleted of endogenous lipid by detergent exchange has been reconstituted into vesicles with synthetic lipids of known head group and fatty acid composition and enzymic activities have been measured. No evidence for head group specificity was found. However, the enzyme does require the fluid environment provided by unsaturated fatty acids. The state of dispersion of the enzyme was found to affect the activities regenerated in reconstitution studies. The highest activities were obtained using lysolecithin containing an oleoyl fatty acid as the lipid component.
Article
1. In the inner mitochondrial membrane, dehydrogenases and cytochromes appear to act independently of each other, and electron transport has been proposed to occur through a mobile pool of ubiquinone-10 molecules [Kröger & Klingenberg (1973) Eur. J. Biochem. 34, 358--368]. 2. Such behaviour can be restored to the interaction between purified Complex I and Complex III by addition of phospholipid and ubiquinone-10 to a concentrated mixture of the Complexes before dilution. 3. A model is proposed for the interaction of Complex I with Complex III in the natural membrane that emphasizes relative mobility of the Complexes rather than ubiquinone-10. Electron transfer occurs only through stoicheiometric Complex I-Complex III units, which, however, are formed and re-formed at rates higher than the rate of electron transfer.
Article
1. The NADH-ubiquinone oxidoreductase complex (Complex I) and the ubiquinol-cytochrome c oxidoreductase complex (Complex III) combine in a 1:1 molar ratio to give NADH-cytochrome c oxidoreductase (Complex I-Complex III). 2. Experiments on the inhibition of the NADH-cytochrome c oxidoreductase activity of mixtures of Complexes I and III by rotenone and antimycin indicate that electron transfer between a unit of Complex I-Complex III and extra molecules of Complexes I or III does not contribute to the overall rate of cytochrome c reduction. 3. The reduction by NADH of the cytochrome b of mixtures of Complexes I and III is biphasic. The extents of the fast and slow phases of reduction are determined by the proportion of the total Complex III specifically associated with Complex I. 4. Activation-energy measurements suggest that the structural features of the Complex I-Complex III unit promote oxidoreduction of endogenous ubiquinone-10.
Article
The degree of freedom for lateral translational diffusion by cytochrome c oxidase and other integral proteins in the energy-transducing membrane of the mitochondrion was determined by combining the use of an immunoglobulin probe monospecific for the oxidase with thermotropic lipid phase transitions. Lateral mobility of the oxidase was monitored by observing the distribution of the immunoglobulin probe on the membrane surface by deep-etch electron microscopy and by observing the distribution of intramembrane particles (integral proteins) in the hydrophobic interior of the membrane by freeze-fracture electron microscopy. Incubation of the membrane with the immunoglobulin resulted in a time-dependent clustering of predominantly large intramembrane particles. Low temperature-induced lipid phase transitions resulted in the close packing of all intramembrane particles and cytochrome c oxidase by lateral exclusion from domains of gel-state bilayer lipid and was completely reversible. However, when cytochrome c oxidase was crosslinked through an immunoglobulin lattice prior to returning the membrane to above the lipid phase transition temperature, small intramembrane particles rerandomized while the large oxidase-related particles remained clustered. These observations reveal that cytochrome c oxidase can diffuse laterally in the energy-transducing membrane, either independently of all other integral proteins or in physical union with one or more other integral proteins. In addition, many other as yet unidentified smaller integral proteins can diffuse independently of the oxidase.
Article
Deuterium nuclear magnetic resonance spectra of 1 -myristoyl-2- ( 14', 14', 1 4'-ZH3) myristoylphosphatidylcholine (DMPC-d3), 1,2- ( 16', 16',16'-ZH3)dipalmit~ylpho~phatidyl- choline (DPPC-d,), 1-( 16',16',16'-*H3)palmitoyl-2-palrnito- leylphosphatidylcholine (PPPC-d3), and 1-myristoyl-2-(6',- 6'-2H2)myri~t~ylphosphatidylcholine (DMPC-2-(6',6'-d2)) have been obtained in the presence of cytochrome oxidase (fer- rccytochrome c:Oz oxidoreductase, EC 1.9.3.1) as a function of temperature and composition and for the pure lipid as a function of temperature by using the quadrupole-echo Fourier transform method at 34.1 MHz. Above T,, the temperature of the gel-to-liquid crystal phase transition of the pure phospholipid, all of the spectra have a single quadrupole splitting with no evidence of a second component. For DMPC-d3 the splitting at - 30 OC decreases monotonically with cytochrome oxidase concentration from -3.7 kHz in the pure lipid to -2.6 kHz at 90 wt % protein. Plots of quad- rupole splitting vs. protein-lipid ratio are linear, indicating that a simple two-site exchange model may be sufficient to account for the results observed. This shows that the methyl groups are "less ordered" in the "boundary lipid" than in the free lipid bilayer. Moreover, the exchange between the two sites is fast enough (>lo3 s-') to average out their I-kHz difference in splitting. Similar, less extensive results were obtained for the other methyl-labeled lipids. However, DMPC-2-(6',6'-d2) with 67 wt % cytochrome oxidase has a spectrum with somewhat In the past 10 years there has been considerable interest in applying "physical" techniques, such as scanning calorimetry, electron spin resonance (ESR),' neutron diffraction, Raman spectroscopy, nuclear magnetic resonance (NMR) spectros- copy, X-ray diffraction, and fluorescence spectroscopy, to study the structure of cell membranes (see, for example, Oldfield et al. (1978a) and references cited therein). It is hoped that a better understanding of membrane structure will eventually lead to a better understanding of membrane function. A
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This chapter describes the preparation and properties of the enzymes and enzyme complexes of the mitochondrial oxidative phosphorylation system. The enzymes concerned with electron transport from NAD(P)H and succinate to molecular oxygen, energy conservation and transduction, and adenosine triphosphate (ATP) synthesis and hydrolysis are located in the mitochondrial inner membrane. Systematic fractionation of this membrane has shown that these enzymes are contained mainly in five protein–lipid complexes. This results in precipitation of complexes I, II, and III, which are separated by centrifugation from complex V in the supernatant. Then, the binary complex I–III is separated from II–III by precipitation with ammonium acetate, and finally I–III and II–III are resolved and separated into I, II, and III, using cholate and ammonium sulfate. The fractionation procedure involves the use of deoxycholate and cholate in conjunction with KCI, a neutral salt of low ionic strength, for membrane solubilization, and of ammonium acetate and ammonium sulfate for precipitation of the desired fragments.
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The interaction between cytochrome c oxidase complex and adenosine triphosphate synthase (F1F0) complex in the purified, dispersed state and embedded in phospholipid vesicles was studied by differential scanning calorimetry and by spin-label electron paramagnetic resonance. The detergent-dispersed cytochrome oxidase and F1F0 complexes undergo endothermic thermodenaturation. However, when these complexes are embedded in phospholipid vesicles, they undergo exothermic thermodenaturation. The energy released is believed to result from the collapse of a strained interaction between unsaturated fatty acyl groups of phospholipids and an exposed area of the complex formed by the removal of interacting proteins. The exothermic enthalpy change of thermodenaturation of a protein-phospholipid exothermic enthalpy change of thermodenaturation of a protein-phospholipid vesicle containing both cytochrome oxidase complex and F1F0 was smaller than that of a mixture of protein-phospholipid vesicles formed from each individual electron transfer complex. This suggests specific interaction between cytochrome oxidase complex and F1F0 in the membrane. Further evidence for interaction between these two complexes is provided by saturation transfer EPR studies in which the rotational correlation time of spin-labeled cytochrome oxidase increases significantly when the complex is mixed with F1F0 prior to being embedded in phospholipid vesicles. From these results, it is concluded that at least a part of cytochrome oxidase and a part of F1F0 form a supermacromolecular complex in the inner mitochondrial membrane. No such supermacromolecular complex is detected between F1F0 and ubiquinol--cytochrome c reductase.
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The saturation kinetics of NADH and succinate oxidation for Coenzyme Q (CoQ) has been re-investigated in pentane-extracted lyophilized beef heart mitochondria reconstituted with exogenous CoQ10. The apparent 'Km' for CoQ10 was one order of magnitude lower in succinate cytochrome c reductase than in NADH cytochrome c reductase. The Km value in NADH oxidation approaches the natural CoQ content of beef heart mitochondria, whereas that in succinate oxidation is close to the content of respiratory chain enzymes.
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The etiology of nerve cell death in neuronal degenerative disease is unknown, but it has been hypothesized that excitotoxic mechanisms may play a role. Such mechanisms may play a role in diseases such as Huntington's disease, Parkinson's disease, amyotropic lateral sclerosis, and Alzheimer's disease. In these illnesses, the slowly evolving neuronal death is unlikely to be due to a sudden release of glutamate, such as occurs in ischemia. One possibility, however, is that a defect in mitochondrial energy metabolism could secondarily lead to slow excitotoxic neuronal death, by making neurons more vulnerable to endogenous glutamate. With reduced oxidative metabolism and partial cell membrane depolarization, voltage-dependent N-methyl-D-aspartate (NMDA) receptor ion channels would be more easily activated. In addition, several other processes involved in buffering intracellular calcium may be impaired. Recent studies in experimental animals showed that mitochondrial toxins can result in a pattern of neuronal degeneration closely resembling that seen in Huntington's disease, which can be blocked with NMDA antagonists. NMDA antagonists also block neuronal degeneration induced by 1-methyl-4-phenylpyridium, which has been implicated in experimental models of Parkinson's disease. The delayed onset of neurodegenerative illnesses could be related to the progressive impairment of mitochondrial oxidative phosphorylation, which accompanies normal aging. If defective mitochondrial energy metabolism plays a role in cell death in neurodegenerative disorders, potential therapeutic strategies would be to use excitatory amino acid antagonists or agents to bypass bioenergetic defects.
Article
This study examines the possible role of Coenzyme Q (CoQ, ubiquinone) in the control of mitochondrial electron transfer. The CoQ concentration in mitochondria from different tissues was investigated by HPLC. By analyzing the rates of electron transfer as a function of total CoQ concentration, it was calculated that, at physiological CoQ concentration NADH cytochrome c reductase activity is not saturated. Values for theoretical Vmax could not be reached experimentally for NADH oxidation, because of the limited miscibility of CoQ10 with the phospholipids. On the other hand, it was found that CoQ3 could stimulate alpha-glycerophosphate cytochrome c reductase over three-fold. Electron transfer being a diffusion-coupled process, we have investigated the possibility of its being subjected to diffusion control. A reconstruction study of Complex I and Complex III in liposomes showed that NADH cytochrome c reductase was not affected by changing the average distance between complexes by varying the protein: lipid ratios. The results of a broad investigation on ubiquinol cytochrome c reductase in bovine heart submitochondrial particles indicated that the enzymic rate is not diffusion-controlled by ubiquinol, whereas the interaction of cytochrome c with the enzyme is clearly diffusion-limited.
Article
To explore the influence of the long isoprene chain of ubiquinone 10 (UQ) on the mobility of the molecule in a phospholipid bilayer, we have synthesized a fluorescent derivative of the head-group moiety of UQ and measured its lateral diffusion in inner membranes of giant mitochondria and in large unilamellar vesicles. The diffusion coefficients, determined by the technique of fluorescence redistribution after photobleaching, were 3.1 X 10(-9) cm2 s-1 in mitochondria and 1.1 X 10(-8) cm2 s-1 in vesicles. Similar diffusion rates were observed for fluorescently labeled phosphatidylethanolamine (PE) with the same moiety attached to its head group (4-nitro-2,1,3-benzooxadiazole: NBD). Fluorescence emission studies carried out in organic solvents of different dielectric constants, and in vesicles and mitochondrial membranes, indicate that NBDUQ is located in a more hydrophobic environment than NBDPE or the starting material IANBD (4-[N-[(iodoacetoxy)ethyl]-N-methylamino]-7-nitro-2,1,3- benzoxadiazole). Fluorescence quenching studies carried out with CuSO4, a water-soluble quenching agent, also indicate that NBDUQ is located deeper in the membrane than NBDPE. These results suggest that ubiquinone and PE are oriented differently in a membrane, even though their diffusion rates are similar. Conclusions regarding whether or not diffusion of UQ is a rate-limiting step in electron transfer must await a more detailed knowledge of the structural organization and properties of the electron transfer components.
Article
Motion of cytochrome c bound to giant (2-10-micron diam) mitochondria isolated from the waterbug Lethocerus indicus was examined using the technique of fluorescence recovery after photobleaching. Fluorescent cytochrome c was exchanged for native cytochrome c through partly damaged outer membrane. Recovery profiles were not statistically different when the fluorescence from iron-free cytochrome c or fluorescein-labeled cytochrome c was used and were essentially the same in the presence or absence of an uncoupler. In the presence of excess porphyrin cytochrome c, the apparent diffusion coefficient was 6 X 10(-11) cm2/s in 0.3 M sucrose-mannitol-EDTA and 3 X 10(-10) cm2/s in 0.10 M KCl/0.10 M sucrose. At concentrations of porphyrin cytochrome c that are stoichiometric with cytochrome c oxidase and for mitochondria in which excess cytochrome c was washed away, two components were observed in the recovery profile. The diffusion coefficient of the fast component was 1 X 10(-10) cm2/s. The second component showed no recovery during the time scale of measurement (D less than 10(-12) cm2/s). We speculate on the origin of the immobile fraction.
Article
The different possible dispositions of the electron transfer components in electron transfer chains are discussed: (a) random distribution of complexes and ubiquinone with diffusion-controlled collisions of ubiquinone with the complexes, (b) random distribution as above, but with ubiquinone diffusion not rate-limiting, (c) diffusion and collision of protein complexes carrying bound ubiquinone, and (d) solid-state assembly. Discrimination among these possibilities requires knowledge of the mobility of the electron transfer chain components. The collisional frequency of ubiquinone-10 with the fluorescent probe 12-(9-anthroyl)stearate, investigated by fluorescence quenching, is 2.3 × 109 M−1 sec−1 corresponding to a diffusion coefficient in the range of 10−6 cm2/sec (Fato, R., Battino, M., Degli Esposti, M., Parenti Castelli, G., and Lenaz, G.,Biochemistry,25, 3378–3390, 1986); the long-range diffusion of a short-chain polar Q derivative measured by fluorescence photobleaching recovery (FRAP) (Gupte, S., Wu, E. S., Höchli, L., Höchli, M., Jacobson, K., Sowers, A. E., and Hackenbrock, C. R.,Proc. Natl. Acad. Sci. USA 81, 2606–2610, 1984) is 3×10−9 cm2/sec. The discrepancy between these results is carefully scrutinized, and is mainly ascribed to the differences in diffusion ranges measured by the two techniques; it is proposed that short-range diffusion, measured by fluorescence quenching, is more meaningful for electron transfer than long-range diffusion measured by FRAP, or microcollisions, which are not sensed by either method. Calculation of the distances traveled by random walk of ubiquinone in the membrane allows a large excess of collisions per turnover of the respiratory chain. Moreover, the second-order rate constants of NADH-ubiquinone reductase and ubiquinol-cytochromec reductase are at least three orders of magnitude lower than the second-order collisional constant calculated from the diffusion of ubiquinone. The activation energies of either the above activities or integrated electron transfer (NADH-cytochromec reductase) are well above that for diffusion (found to be ca. 1 kcal/mol). Cholesterol incorporation in liposomes, increasing bilayer viscosity, lowers the diffusion coefficients of ubiquinone but not ubiquinol-cytochromec reductase or succinate-cytochromec reductase activities. The decrease of activity by ubiquinone dilution in the membrane is explained by its concentration falling below theK m of the partner enzymes. It is calculated that ubiquinone diffusion is not rate-limiting, favoring a random model of the respiratory chain organization. It is not possible, however, to exclude solid-state assemblies if the rate of dissociation and association of ubiquinone is faster than the turnover of electron transfer.
Article
This review focuses on our studies over the past ten years which reveal that the mitochondrial inner membrane is a fluid-state rather than a solid-state membrane and that all membrane proteins and redox components which catalyze electron transport and ATP synthesis are in constant and independent diffusional motion. The studies reviewed represent the experimental basis for the random collision model of electron transport. We present five fundamental postulates upon which the random collision model of mitochondrial electron transport is founded: All redox components are independent lateral diffusants; Cytochrome c diffuses primarily in three dimensions; Electron transport is a diffusion-coupled kinetic process; Electron transport is a multicollisional, obstructed, long-range diffusional process; The rates of diffusion of the redox components have a direct influence on the overall kinetic process of electron transport and can be rate limiting, as in diffusion control. The experimental rationales and the results obtained in testing each of the five postulates of the random collision model are presented. In addition, we offer the basic concepts, criteria and experimental strategies that we believe are essential in considering the significance of the relationship between diffusion and electron transport. Finally, we critically explore and assess other contemporary studies on the diffusion of inner membrane components related to electron transport including studies on: rotational diffusion, immobile fractions, complex formation, dynamic aggregates, and rates of diffusion. Review of all available data confirms the random collision model and no data appear to exist that contravene it. It is concluded that mitochondrial electron transport is a diffusion-based random collision process and that diffusion has an integral and controlling affect on electron transport.
Article
The interaction between succinate-ubiquinone and ubiquinol-cytochrome c reductases in the purified, dispersed state and in embedded phospholipid vesicles was studied by differential scanning calorimetry and by electron paramagnetic resonance (EPR). When the purified, detergent-dispersed succinate-ubiquinone reductase, ubiquinol-cytochrome c reductase, and cytochrome c oxidase undergo thermodenaturation, they show an endothermic transition. However, when these isolated electron-transfer complexes are embedded in phospholipid vesicles, they undergo exothermodenaturation. The energy released could result from the collapse of the strained interaction between unsaturated fatty acyl groups of phospholipids and an exposed area of the complex formed by removal of interacting proteins. The exothermic enthalpy change of thermodenaturation of a protein-phospholipid vesicle containing both succinate-ubiquinone and ubiquinol-cytochrome c reductases was smaller than that of a mixture of protein-phospholipid vesicles formed from the individual electron-transfer complexes. This suggests specific interaction between succinate-ubiquinone reductase and ubiquinol-cytochrome c reductase in the membrane. This idea is supported by saturation transfer EPR studies showing that the rotational correlation time of spin-labeled ubiquinol-cytochrome c reductase is increased when mixed with succinate-ubiquinone reductase prior to embedding in phospholipid vesicles. These results indicate that succinate-ubiquinone reductase and ubiquinol-cytochrome c reductase are indeed present in the membrane as a supermacromolecular complex. No such supermacromolecular complex is detected between NADH-ubiquinone and ubiquinol-cytochrome c reductases or between succinate-ubiquinone and NADH-uniquinone reductases.
Article
The quenching of fluorescence of n-(9-anthroyloxy)stearic acids and other probes by different ubiquinone homologues and analogues has been exploited to assess the localization and lateral mobility of the quinones in lipid bilayers of model and mitochondrial membranes. The true bimolecular collisional quenching constants in the lipids together with the lipid/water partition coefficients were obtained from Stern-Volmer plots at different membrane concentrations. A monomeric localization of the quinone in the phospholipid bilayer is suggested for the short side-chain ubiquinone homologues and for the longer derivatives when cosonicated with the phospholipids. The diffusion coefficients of the ubiquinones, calculated from the quenching constants either in three dimensions or in two dimensions, are in the range of (1-6) X 10(-6) cm2 s-1, both in phospholipid vesicles and in mitochondrial membranes. A careful analysis of different possible locations of ubiquinones in the phospholipid bilayer, accounting for the calculated diffusion coefficients and the viscosities derived therefrom, strongly suggests that the ubiquinone 10 molecule is located within the lipid bilayer with the quinone ring preferentially adjacent to the polar head groups of the phospholipids and the hydrophobic tail largely accommodated in the bilayer midplane. The steady-state rates of either ubiquinol 1-cytochrome c reductase or NADH:ubiquinone 1 reductase are proportional to the concentration of the quinol or quinone substrate in the membrane. The second-order rate constants appear to be at least 3 orders of magnitude lower than the second-order constants for quenching of the fluorescent probes; this is taken as a clear indication that ubiquinone diffusion is not the rate-determining step in the quinone-enzyme interaction.(ABSTRACT TRUNCATED AT 250 WORDS)
Article
A new model for lateral diffusion, the milling crowd model (MC), is proposed and is used to derive the dependence of the monomeric and excimeric fluorescence yields of excimeric membrane probes on their concentration. According to the MC model, probes migrate by performing spatial exchanges with a randomly chosen nearest neighbor (lipid or probe). Only nearest neighbor probes, one of which is in the excited state, may form an excimer. The exchange frequency, and hence the local lateral diffusion coefficient, may then be determined from experiment with the aid of computer simulation of the excimer formation kinetics. The same model is also used to study the long-range lateral diffusion coefficient of probes in the presence of obstacles (e.g., membrane proteins). The dependence of the monomeric and excimeric fluorescence yields of 1-pyrene-dodecanoic acid probes on their concentration in the membranes of intact erythrocytes was measured and compared with the prediction of the MC model. The analysis yields an excimer formation rate for nearest neighbor molecules of approximately 1 X 10(7) s-1 and an exchange frequency of approximately greater than 2 X 10(7) s-1, corresponding to a local diffusion coefficient of greater than 3 X 10(-8) cm2 s-1. This value is several times larger than the long-range diffusion coefficient for a similar system measured in fluorescence photobleaching recovery experiments. The difference is explained by the fact that long-range diffusion is obstructed by dispersed membrane proteins and is therefore greatly reduced when compared to free diffusion. The dependence of the diffusion coefficient on the fractional area covered by obstacles and on their size is derived from MC simulations and is compared to those of other theories lateral diffusibility.
Article
The electrophoretic freeze-fracture electron microscopy method (Sowers, A.E. and Hackenbrock, C.R. (1984) Proc. Natl. Acad. Sci. USA 78, 6246-6250) for measuring the lateral diffusion coefficient of integral proteins was applied to a large population of spherical-shaped mitochondrial inner membranes. Membrane integral protein concentration was estimated by determining the intramembrane particle concentration. Analysis of the data reveals that: (a) the radii of the spherical inner membranes in the selected population ranged from 0.22 to 1.2 micron, (b) the intramembrane particle concentrations ranged from 2300 to 6400 per micron2, and (c) the calculated lateral diffusion coefficients of the intramembrane particles ranged from 1.3 X 10(-10) to 3.35 X 10(-9) cm2/s. The data clearly show a naturally occurring large range in protein concentration in the mitochondrial inner membrane and an inverse correlation of lateral diffusion coefficient with the membrane protein concentration. This study is the first to show that the lateral diffusion coefficient of integral proteins in a native membrane varies as the membrane protein concentration.