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See detailAtypical composition and structure of the mitochondrial dimeric ATP synthase from Euglena gracilis
Yadav, K.N. Sathish; Miranda Astudillo, Héctor Vicente ULiege; Colina-Tenorio, Lili et al

in Biochimica et Biophysica Acta-Bioenergetics (2017), 1858(4), 267-275

Mitochondrial respiratory-chain complexes from Euglenozoa comprise classical subunits described in other eukaryotes (i.e. mammals and fungi) and subunits that are restricted to Euglenozoa (e.g. Euglena ... [more ▼]

Mitochondrial respiratory-chain complexes from Euglenozoa comprise classical subunits described in other eukaryotes (i.e. mammals and fungi) and subunits that are restricted to Euglenozoa (e.g. Euglena gracilis and Trypanosoma brucei). Here we studied the mitochondrial F1FO-ATP synthase (or Complex V) from the photosynthetic eukaryote E. gracilis in detail. The enzyme was purified by a two-step chromatographic procedure and its subunit composition was resolved by a three-dimensional gel electrophoresis (BN/SDS/SDS). Twenty-two different subunits were identified by mass-spectrometry analyses among which the canonical alpha, beta, gamma, delta, epsilon and OSCP subunits, and at least seven subunits previously found in Trypanosoma. The ADP/ATP carrier was also associated to the ATP synthase into a dimeric ATP synthasome. Single-particle analysis by transmission electron microscopy of the dimeric ATP synthase indicated that the structures of both the catalytic and central rotor parts are conserved while other structural features are original. These new features include a large membrane-spanning region joining the monomers, an external peripheral stalk and a structure that goes through the membrane and reaches the inter membrane space below the c-ring, the latter having not been reported for any mitochondrial F-ATPase. [less ▲]

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See detailNear-neighbor interactions of the membrane-embedded subunits of the mitochondrial ATP synthase of a chlorophycean alga
Sánchez-Vásquez, Lorenzo; Vázquez-Acevedo, M; de la Mora, J et al

in Biochimica et Biophysica Acta-Bioenergetics (2017), 1858(7), 497-509

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See detailDissecting the peripheral stalk of the mitochondrial ATP synthase of chlorophycean algae.
Vázquez-Acevedo, M; Vega de Luna, F; Sánchez-Vásquez, L et al

in Biochimica et Biophysica Acta-Bioenergetics (2016), 1857(8), 1183-90

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See detailPlant mitochondrial complex I composition and assembly: a review
Subrahmanian, Nitya; Remacle, Claire ULiege; Hamel, Patrice

in Biochimica et Biophysica Acta-Bioenergetics (2016), 1857(7), 1001-1014

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See detailDissecting the peripheral stalk of the mitochondrial ATP synthase of chlorophycean algae
Vázquez-Acevedo, Miriam; Vega-deLuna, Félix; Sánchez-Vásquez, Lorenzo et al

in Biochimica et Biophysica Acta-Bioenergetics (2016), 1857(8), 1183-1190

The algae Chlamydomonas reinhardtii and Polytomella sp., a green and a colorless member of the chlorophycean lineage respectively, exhibit a highly-stable dimeric mitochondrial F1Fo-ATP synthase (complex ... [more ▼]

The algae Chlamydomonas reinhardtii and Polytomella sp., a green and a colorless member of the chlorophycean lineage respectively, exhibit a highly-stable dimeric mitochondrial F1Fo-ATP synthase (complex V), with a molecular mass of 1600kDa. Polytomella, lacking both chloroplasts and a cell wall, has greatly facilitated the purification of the algal ATP-synthase. Each monomer of the enzyme has 17 polypeptides, eight of which are the conserved, main functional components, and nine polypeptides (Asa1 to Asa9) unique to chlorophycean algae. These atypical subunits form the two robust peripheral stalks observed in the highly-stable dimer of the algal ATP synthase in several electron-microscopy studies. The topological disposition of the components of the enzyme has been addressed with cross-linking experiments in the isolated complex; generation of subcomplexes by limited dissociation of complex V; detection of subunit-subunit interactions using recombinant subunits; in vitro reconstitution of subcomplexes; silencing of the expression of Asa subunits; and modeling of the overall structural features of the complex by EM image reconstruction. Here, we report that the amphipathic polymer Amphipol A8-35 partially dissociates the enzyme, giving rise to two discrete dimeric subcomplexes, whose compositions were characterized. An updated model for the topological disposition of the 17 polypeptides that constitute the algal enzyme is suggested. This article is part of a Special Issue entitled 'EBEC 2016: 19th European Bioenergetics Conference, Riva del Garda, Italy, July 2-6, 2016', edited by Prof. Paolo Bernardi. [less ▲]

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See detailSubunit Asa1 spans all the peripheral stalk of the mitochondrial ATP synthase of the chlorophycean alga Polytomella sp.
Colina-Tenorio, Lilia; Miranda Astudillo, Héctor Vicente ULiege; Cano-Estrada, Araceli et al

in Biochimica et Biophysica Acta-Bioenergetics (2015), 1857(4), 359-369

Mitochondrial F1FO-ATP synthase of chlorophycean algae is dimeric. It contains eight orthodox subunits (alpha, beta, gamma, delta, epsilon, OSCP, a and c) and nine atypical subunits (Asa1 to 9). These ... [more ▼]

Mitochondrial F1FO-ATP synthase of chlorophycean algae is dimeric. It contains eight orthodox subunits (alpha, beta, gamma, delta, epsilon, OSCP, a and c) and nine atypical subunits (Asa1 to 9). These subunits build the peripheral stalk of the enzyme and stabilize its dimeric structure. The location of the 66.1 kDa subunit Asa1 has been debated. On one hand, it was found in a transient subcomplex that contained membrane-bound subunits Asa1/Asa3/Asa5/Asa8/a (Atp6)/c (Atp9). On the other hand, Asa1 was proposed to form the bulky structure of the peripheral stalk that contacts the OSCP subunit in the F1 sector. Here, we overexpressed and purified the recombinant proteins Asa1 and OSCP and explored their interactions in vitro, using immunochemical techniques and affinity chromatography. Asa1 and OSCP interact strongly, and the carboxy-terminal half of OSCP seems to be instrumental for this association. In addition, the algal ATP synthase was partially dissociated at relatively high detergent concentrations, and an Asa1/Asa3/Asa5/Asa8/a/c10 subcomplex was identified. Furthermore, Far-Western analysis suggests an Asa1-Asa8 interaction. Based on these results, a model is proposed in which Asa1 spans the whole peripheral arm of the enzyme, from a region close to the matrix-exposed side of the mitochondrial inner membrane to the F1 region where OSCP is located. 3D models show elongated, helix-rich structures for chlorophycean Asa1 subunits. Asa1 subunit probably plays a scaffolding role in the peripheral stalk analogous to the one of subunit b in orthodox mitochondrial enzymes. [less ▲]

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See detailEvidence of oxidative stress and mitochondrial respiratory chain dysfunction in an in vitro model of sepsis-induced kidney injury
Quoilin, Caroline ULiege; Mouithys-Mickalad, Ange ULiege; Lécart, Sandrine et al

in Biochimica et Biophysica Acta-Bioenergetics (2014), 1837(10), 1790-1800

To investigate the role of oxidative stress and/or mitochondrial impairment in the occurrence of acute kidney injury (AKI) during sepsis, we developed a sepsis-induced in vitro model using proximal ... [more ▼]

To investigate the role of oxidative stress and/or mitochondrial impairment in the occurrence of acute kidney injury (AKI) during sepsis, we developed a sepsis-induced in vitro model using proximal tubular epithelial cells exposed to a bacterial endotoxin (lipopolysaccharide, LPS). This investigation has provided key features on the relationship between oxidative stress and mitochondrial respiratory chain activity defects. LPS treatment resulted in an increase in the expression of inducible nitric oxide synthase (iNOS) and NADPH oxidase 4 (NOX-4), suggesting the cytosolic overexpression of nitric oxide and superoxide anion, the primary reactive nitrogen species (RNS) and reactive oxygen species (ROS). This oxidant state seemed to interrupt mitochondrial oxidative phosphorylation by reducing cytochrome c oxidase activity. As a consequence, disruptions in the electron transport and the proton pumping across the mitochondrial inner membrane occurred, leading to a decrease of the mitochondrial membrane potential, a release of apoptotic-inducing factors and a depletion of adenosine triphosphate. Interestingly, after being targeted by RNS and ROS, mitochondria became in turn producer of ROS, thus contributing to increase the mitochondrial dysfunction. The role of oxidants in mitochondrial dysfunction was further confirmed by the use of iNOS inhibitors or antioxidants that preserve cytochrome c oxidase activity and prevent mitochondrial membrane potential dissipation. These results suggest that sepsis-induced AKI should not only be regarded as failure of energy status but also as an integrated response, including transcriptional events, ROS signaling, mitochondrial activity and metabolic orientation such as apoptosis. [less ▲]

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See detailAnalysis of PSII antenna size heterogeneity of Chlamydomonas reinhardtii during state transitions
de Marchin, Thomas ULiege; Ghysels, Bart ULiege; Nicolay, Samuel ULiege et al

in Biochimica et Biophysica Acta-Bioenergetics (2014), 1837(1), 121-130

PSII antenna size heterogeneity has been intensively studied in the past. Based on DCMU fluorescence rise kinetics, multiple types of photosystems with different properties were described. However, due to ... [more ▼]

PSII antenna size heterogeneity has been intensively studied in the past. Based on DCMU fluorescence rise kinetics, multiple types of photosystems with different properties were described. However, due to the complexity of fluorescence signal analysis, multiple questions remain unanswered. The number of different types of PSII is still debated as well as their degree of connectivity. In Chlamydomonas reinhardtii we found that PSIIα possesses a high degree of connectivity and an antenna 2-3 times larger than PSIIβ, as described previously. We also found some connectivity for PSIIβ in contrast with the majority of previous studies. This is in agreement with biochemical studies which describe PSII mega-, super- and core- complexes in Chlamydomonas. In these studies, the smallest unit of PSII in vivo would be a dimer of two core complexes hence allowing connectivity. We discuss the possible relationships between PSIIα and PSIIβ and the PSII mega-, super- and core- complexes. We also showed that strain and medium dependent variations in the half-time of the fluorescence rise can be explained by variations in the proportions of PSIIα and PSIIβ. When analyzing the state transition process in vivo, we found that this process induces an inter-conversion of PSIIα and PSIIβ. During a transition from state 2 to state 1, DCMU fluorescence rise kinetics are satisfactorily fitted by considering two PSII populations with constant kinetic parameters. We discuss our findings about PSII heterogeneity during state transitions in relation with recent results on the remodeling of the pigment-protein PSII architecture during this process. [less ▲]

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See detailInteractions of subunits Asa2, Asa4 and Asa7 in the peripheral stalk of the mitochondrial ATP synthase of the chlorophycean alga Polytomella sp.
Miranda-Astudillo, Hector; Cano-Estrada, Araceli; Vazquez-Acevedo, Miriam et al

in Biochimica et Biophysica Acta-Bioenergetics (2014), 1837

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See detailInteractions of subunits Asa2, Asa4 and Asa7 in the peripheral stalk of the mitochondrial ATP synthase of the chlorophycean alga Polytomella sp.
Miranda Astudillo, Héctor Vicente ULiege; Cano-Estrada, Arceli; Vázquez-Acevedo, Miriam et al

in Biochimica et Biophysica Acta-Bioenergetics (2013), 1837(1), 1-13

Mitochondrial F1FO-ATP synthase of chlorophycean algae is a complex partially embedded in the inner mitochondrial membrane that is isolated as a highly stable dimer of 1600 kDa. It comprises 17 ... [more ▼]

Mitochondrial F1FO-ATP synthase of chlorophycean algae is a complex partially embedded in the inner mitochondrial membrane that is isolated as a highly stable dimer of 1600 kDa. It comprises 17 polypeptides, nine of which (subunits Asa1 to 9) are not present in classical mitochondrial ATP synthases and appear to be exclusive of the chlorophycean lineage. In particular, subunits Asa2, Asa4 and Asa7 seem to constitute a section of the peripheral stalk of the enzyme. Here, we over-expressed and purified subunits Asa2, Asa4 and Asa7 and the corresponding amino-terminal and carboxy-terminal halves of Asa4 and Asa7 in order to explore their interactions in vitro, using immunochemical techniques, blue native electrophoresis and affinity chromatography. Asa4 and Asa7 interact strongly, mainly through their carboxy-terminal halves. Asa2 interacts with both Asa7 and Asa4, and also with subunit ?? in the F1 sector. The three Asa proteins form an Asa2/Asa4/Asa7 subcomplex. The entire Asa7 and the carboxy-terminal half of Asa4 seem to be instrumental in the interaction with Asa2. Based on these results and on computer-generated structural models of the three subunits, we propose a model for the Asa2/Asa4/Asa7 subcomplex and for its disposition in the peripheral stalk of the algal ATP synthase. [less ▲]

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See detailMitochondrial NADH:ubiquinone oxidoreductase (complex I) in eukaryotes: A highly conserved subunit composition highlighted by mining of protein databases
Cardol, Pierre ULiege

in Biochimica et Biophysica Acta-Bioenergetics (2011), 11

Complex I (NADH:ubiquinone oxidoreductase) is the largest enzyme of the mitochondrial respiratory chain. Compared to its bacterial counterpart which encompasses 14-17 subunits, mitochondrial complex I has ... [more ▼]

Complex I (NADH:ubiquinone oxidoreductase) is the largest enzyme of the mitochondrial respiratory chain. Compared to its bacterial counterpart which encompasses 14-17 subunits, mitochondrial complex I has almost tripled its subunit composition during evolution of eukaryotes, by recruitment of so-called accessory subunits, part of them being specific to distinct evolutionary lineages. The increasing availability of numerous broadly sampled eukaryotic genomes now enables the reconstruction of the evolutionary history of this large protein complex. Here, a combination of profile-based sequence comparisons and basic structural properties analyses at the protein level enabled to pinpoint homology relationships between complex I subunits from fungi, mammals or green plants, previously identified as "lineage-specific" subunits. In addition, homologs of at least 40 mammalian complex I subunits are present in representatives of all major eukaryote assemblages, half of them having not been investigated so far (Excavates, Chromalveolates, Amoebozoa). This analysis revealed that complex I was subject to a phenomenal increase in size that predated the diversification of extant eukaryotes, followed by very few lineage-specific additions/losses of subunits. The implications of this subunit conservation for studies of complex I are discussed. [less ▲]

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See detailSubunit-subunit interactions and overall topology of the dimeric mitochondrial ATP synthase of Polytomella sp
Cano-Estrada, Araceli; Vázquez-Acevedo, Miriam; Villavicencio-Queijeiro, Alexa et al

in Biochimica et Biophysica Acta-Bioenergetics (2010), 1797(8), 1439-1448

Mitochondrial F1F0-ATP synthase of chlorophycean algae is a dimeric complex of 1600kDa constituted by 17 different subunits with varying stoichiometries, 8 of them conserved in all eukaryotes and 9 that ... [more ▼]

Mitochondrial F1F0-ATP synthase of chlorophycean algae is a dimeric complex of 1600kDa constituted by 17 different subunits with varying stoichiometries, 8 of them conserved in all eukaryotes and 9 that seem to be unique to the algal lineage (subunits ASA1-9). Two different models proposing the topological assemblage of the nine ASA subunits in the ATP synthase of the colorless alga Polytomella sp. have been put forward. Here, we readdressed the overall topology of the enzyme with different experimental approaches: detection of close vicinities between subunits based on cross-linking experiments and dissociation of the enzyme into subcomplexes, inference of subunit stoichiometry based on cysteine residue labelling, and general three-dimensional structural features of the complex as obtained from small-angle X-ray scattering and electron microscopy image reconstruction. Based on the available data, we refine the topological arrangement of the subunits that constitute the mitochondrial ATP synthase of Polytomella sp. [less ▲]

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See detailLoss of mitochondrial ATP synthase subunit beta (Atp2) alters mitochondrial and chloroplastic function and morphology in Chlamydomonas.
Lapaille, M.; Thiry, Marc ULiege; Perez, E. et al

in Biochimica et Biophysica Acta-Bioenergetics (2010), 1797

Mitochondrial F(1)F(O) ATP synthase (Complex V) catalyses ATP synthesis from ADP and inorganic phosphate using the proton-motive force generated by the substrate-driven electron transfer chain. In this ... [more ▼]

Mitochondrial F(1)F(O) ATP synthase (Complex V) catalyses ATP synthesis from ADP and inorganic phosphate using the proton-motive force generated by the substrate-driven electron transfer chain. In this work, we investigated the impact of the loss of activity of the mitochondrial enzyme in a photosynthetic organism. In this purpose, we inactivated by RNA interference the expression of the ATP2 gene, coding for the catalytic subunit beta, in the green alga Chlamydomonas reinhardtii. We demonstrate that in the absence of beta subunit, complex V is not assembled, respiratory rate is decreased by half and ATP synthesis coupled to the respiratory activity is fully impaired. Lack of ATP synthase also affects the morphology of mitochondria which are deprived of cristae. We also show that mutants are obligate phototrophs and that rearrangements of the photosynthetic apparatus occur in the chloroplast as a response to ATP synthase deficiency in mitochondria. Altogether, our results contribute to the understanding of the yet poorly studied bioenergetic interactions between organelles in photosynthetic organisms. [less ▲]

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See detailSubunit-subunit interactions and overall topology of the dimeric mitochondrial ATP synthase of Polytomella sp.
Cano-Estrada, A.; Vazquez-Acevedo, M.; Villavicencio-Queijeiro, A. et al

in Biochimica et Biophysica Acta-Bioenergetics (2010), 1797

Mitochondrial F(1)F(0)-ATP synthase of chlorophycean algae is a dimeric complex of 1600kDa constituted by 17 different subunits with varying stoichiometries, 8 of them conserved in all eukaryotes and 9 ... [more ▼]

Mitochondrial F(1)F(0)-ATP synthase of chlorophycean algae is a dimeric complex of 1600kDa constituted by 17 different subunits with varying stoichiometries, 8 of them conserved in all eukaryotes and 9 that seem to be unique to the algal lineage (subunits ASA1-9). Two different models proposing the topological assemblage of the nine ASA subunits in the ATP synthase of the colorless alga Polytomella sp. have been put forward. Here, we readdressed the overall topology of the enzyme with different experimental approaches: detection of close vicinities between subunits based on cross-linking experiments and dissociation of the enzyme into subcomplexes, inference of subunit stoichiometry based on cysteine residue labelling, and general three-dimensional structural features of the complex as obtained from small-angle X-ray scattering and electron microscopy image reconstruction. Based on the available data, we refine the topological arrangement of the subunits that constitute the mitochondrial ATP synthase of Polytomella sp. [less ▲]

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See detailPlasticity of the mitoproteome to nitrogen sources (nitrate and ammonium) in Chlamydomonas reinhardtii: the logic of Aox1 gene localization
Gérin, Stéphanie ULiege; Mathy, Grégory ULiege; Blomme, Arnaud ULiege et al

in Biochimica et Biophysica Acta-Bioenergetics (2010), 1797

Nitrate and ammonium constitute primary inorganic nitrogen sources that can be incorporated into carbon skeletons in photosynthetic eukaryotes. In Chlamydomonas, previous studies and the present one ... [more ▼]

Nitrate and ammonium constitute primary inorganic nitrogen sources that can be incorporated into carbon skeletons in photosynthetic eukaryotes. In Chlamydomonas, previous studies and the present one showed that the mitochondrial AOX is up-regulated in nitrate-grown cells in comparison with ammonium-grown cells. In this work, we have performed a comparative proteomic analysis of the soluble mitochondrial proteome of Chlamydomonas cells growth either on nitrate or ammonium. Our results highlight important proteomics modifications mostly related to primary metabolism in cells grown on nitrate. We could note an up-regulation of some TCA cycle enzymes and a down-regulation of cytochrome c1 together with an up-regulation of l-arginine and purine catabolism enzymes and of ROS scavenging systems. Hence, in nitrate-grown cells, AOX may play a dual role: (1) lowering the ubiquinone pool reduction level and (2) permitting the export of mitochondrial reducing power under the form of malate for nitrate and nitrite reduction. This role of AOX in the mitochondrial plasticity makes logical the localization of Aox1 in a nitrate assimilation gene cluster. [less ▲]

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See detailRegulation of Acanthamoeba castellanii alternative oxidase activity by mutual exclusion of purine nucleotides; ATP's inhibitory effect.
Woyda-ploszczyca, A.; Sluse, Francis ULiege; Jarmuszkiewicz, W.

in Biochimica et Biophysica Acta-Bioenergetics (2009), 1787

The effects of different adenine and guanine nucleotides on the cyanide-resistant respiration (i.e. alternative oxidase (AcAOX) activity) of mitochondria from the amoeba A. castellanii mitochondria were ... [more ▼]

The effects of different adenine and guanine nucleotides on the cyanide-resistant respiration (i.e. alternative oxidase (AcAOX) activity) of mitochondria from the amoeba A. castellanii mitochondria were studied. We found that guanine nucleotides activate AcAOX to a greater degree than adenine nucleotides, and that nucleoside monophosphates were more efficient activators than nucleoside di- or triphosphates. The extent of the nucleotides' influence on AcAOX was dependent on the medium's pH and was more pronounced at pH 6.8, which is optimal for AcAOX activity. In contrast to other purine nucleosides, we demonstrate, for the first time, that ATP has an inhibitory effect on AcAOX activity. Since we also observed the inhibition by ATP in the mitochondria of another protozoon, such as Dictyostelium discoideum, and the yeast, Candida maltosa, it may be a regulatory feature common to all purine nucleotide-modulated non-plant AOXs. The physiological importance of this discovery is discussed. Kinetic data show that the binding of GMP (a positive allosteric effector) and the binding of ATP (a negative allosteric effector) to AcAOX are mutually exclusive. ATP's inhibition of the enzyme can be overcome by sufficiently high concentrations of GMP, and conversely, GMP's stimulation can be overcome by sufficiently high concentrations of ATP. However, an approximately three times lower concentration of GMP compared to ATP gives a half maximal effect on AcAOX activity. This is indicative of a higher binding affinity for the positive effector at the same or, at least overlapping, nucleotide-binding sites on AcAOX. These results suggest that AcAOX activity in A. castellanii mitochondria might be controlled by the relative intracellular concentrations of purine nucleotides. [less ▲]

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See detailMitochondrial comparative proteomics: Strenghts and Pitfalls
Mathy, Grégory ULiege; Sluse, Francis ULiege

in Biochimica et Biophysica Acta-Bioenergetics (2008), 1977

In this review, we describe the various techniques available to carry out valid comparative proteomics, their advantages and their disadvantages according to the goal of the research. Two-dimensional ... [more ▼]

In this review, we describe the various techniques available to carry out valid comparative proteomics, their advantages and their disadvantages according to the goal of the research. Two-dimensional electrophoresis and 2D-DIGE are compared to shotgun proteomics and SILE. We give our opinion on the best fields of application in the domain of comparative proteomics. We emphasize the usefulness of these new tools, providing mass data to study physiology and mitochondrial plasticity when faced with a specific mitochondrial insufficiency or exogenic stress. We illustrate the subject with results obtained in our laboratory specifying the importance of an approach of comparative proteomics combined from mitochondria and from the cell, which makes it possible to obtain important information on the status of the mitochondrial function at the cellular level. Finally, we draw attention to the dangers of the extrapolation of proteomic data to metabolic flows which requires the greatest care [less ▲]

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See detailIn Chlamydomonas, the Loss of Nd5 Subunit Prevents the Assembly of Whole Mitochondrial Complex I and Leads to the Formation of a Low Abundant 700 Kda Subcomplex
Cardol, Pierre ULiege; Boutaffala, Layla ULiege; Memmi, S. et al

in Biochimica et Biophysica Acta-Bioenergetics (2008), 1777

In the green alga Chlamydomonas reinhardtii, a mutant deprived of complex I enzyme activity presents a 1T deletion in the mitochondrial nd5 gene. The loss of the ND5 subunit prevents the assembly of the ... [more ▼]

In the green alga Chlamydomonas reinhardtii, a mutant deprived of complex I enzyme activity presents a 1T deletion in the mitochondrial nd5 gene. The loss of the ND5 subunit prevents the assembly of the 950 kDa whole complex I. Instead, a low abundant 700 kDa subcomplex, loosely associated to the inner mitochondrial membrane, is assembled. The resolution of the subcomplex by SDS-PAGE gave rise to 19 individual spots, sixteen having been identified by mass spectrometry analysis. Eleven, mainly associated to the hydrophilic part of the complex, are homologs to subunits of the bovine enzyme whereas five (including gamma-type carbonic anhydrase subunits) are specific to green plants or to plants and fungi. None of the subunits typical of the beta membrane domain of complex I enzyme has been identified in the mutant. This allows us to propose that the truncated enzyme misses the membrane distal domain of complex I but retains the proximal domain associated to the matrix arm of the enzyme. A complex I topology model is presented in the light of our results. Finally, a supercomplex most probably corresponding to complex I-complex III association, was identified in mutant mitochondria, indicating that the missing part of the enzyme is not required for the formation of the supercomplex. [less ▲]

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See detailMitochondrial UCPs: New insights into regulation and impact
Sluse, Francis ULiege; Jarmuszkiewicz, Wieslawa; Navet, Rachel ULiege et al

in Biochimica et Biophysica Acta-Bioenergetics (2006), 1757(5-6, Suppl 1), 101

Uncoupling proteins (UCPs) are mitochondrial inner membrane proteins sustaining an inducible proton conductance. They weaken the proton electrochemical gradient built up by the mitochondrial respiratory ... [more ▼]

Uncoupling proteins (UCPs) are mitochondrial inner membrane proteins sustaining an inducible proton conductance. They weaken the proton electrochemical gradient built up by the mitochondrial respiratory chain. Brown fat UCP1 sustains a free fatty acid (FA)-induced purine nucleotide (PN)-inhibited proton conductance. Inhibition of the proton conductance by PN has been considered as a diagnostic of UCP activity. However, conflicting results have been obtained in isolated mitochondria for UCP homologues (i.e., UCP2, UCP3, plant UCP, and protist UCP) where the FFA-activated proton conductance is poorly sensitive to PN under resting respiration conditions. Our recent work clearly indicates that the membranous coenzyme Q, through its redox state, represents a regulator of the inhibition by PN of FFA-activated UCP1 homologues under phosphorylating respiration conditions. Several physiological roles of UCPs have been suggested, including a control of the cellular energy balance as well as the preventive action against oxidative stress. In this paper, we discuss new information emerging from comparative proteomics about the impact of UCPs on mitochondrial physiology, when recombinant UCP1 is expressed in yeast and when UCP2 is over-expressed in hepatic mitochondria during steatosis [less ▲]

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See detailSubstrate kinetics of the Acanthamoeba castellanii alternative oxidase and the effects of GMP.
Jarmuszkiewicz, W.; Czarna, M.; Sluse, Francis ULiege

in Biochimica et Biophysica Acta-Bioenergetics (2005), 1708

In Acanthamoeba castellanii mitochondria, the apparent affinity values of alternative oxidase for oxygen were much lower than those for cytochrome c oxidase. For unstimulated alternative oxidase, the K ... [more ▼]

In Acanthamoeba castellanii mitochondria, the apparent affinity values of alternative oxidase for oxygen were much lower than those for cytochrome c oxidase. For unstimulated alternative oxidase, the K(Mox) values were around 4-5 microM both in mitochondria oxidizing 1 mM external NADH or 10 mM succinate. For alternative oxidase fully stimulated by 1 mM GMP, the KK(Mox) values were markedly different when compared to those in the absence of GMP and they varied when different respiratory substrates were oxidized (K(Mox) was around 1.2 microM for succinate and around 11 microM for NADH). Thus, with succinate as a reducing substrate, the activation of alternative oxidase (with GMP) resulted in the oxidation of the ubiquinone pool, and a corresponding decrease in K(Mox). However, when external NADH was oxidized, the ubiquinone pool was further reduced (albeit slightly) with alternative oxidase activation, and the K(Mox) increased dramatically. Thus, the apparent affinity of alternative oxidase for oxygen decreased when the ubiquinone reduction level increased either by changing the activator or the respiratory substrate availability. [less ▲]

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