Oxidation of fatty acids and pyruvate in the mitochondrial matrix yield large amounts of NADH. The respiratory electron transport chain couples the re-oxidation of this NADH to NAD+ to the export of protons from the mitochonrial matrix, generating a chemiosmotic gradient across the inner mitochondrial membrane. This gradient is used to drive the synthesis of ATP; it can also be bypassed by uncoupling proteins to generate heat, a reaction in brown fat that may be important in regulation of body temperature in newborn children.
Stanley CA, Hale DE.; ''Genetic disorders of mitochondrial fatty acid oxidation.''; PubMedEurope PMCScholia
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Yoshida S, Tsutsumi S, Muhlebach G, Sourbier C, Lee MJ, Lee S, Vartholomaiou E, Tatokoro M, Beebe K, Miyajima N, Mohney RP, Chen Y, Hasumi H, Xu W, Fukushima H, Nakamura K, Koga F, Kihara K, Trepel J, Picard D, Neckers L.; ''Molecular chaperone TRAP1 regulates a metabolic switch between mitochondrial respiration and aerobic glycolysis.''; PubMedEurope PMCScholia
Fontanesi F, Soto IC, Horn D, Barrientos A.; ''Assembly of mitochondrial cytochrome c-oxidase, a complicated and highly regulated cellular process.''; PubMedEurope PMCScholia
Boyer PD, Cross RL, Momsen W.; ''A new concept for energy coupling in oxidative phosphorylation based on a molecular explanation of the oxygen exchange reactions.''; PubMedEurope PMCScholia
Hirst J, Carroll J, Fearnley IM, Shannon RJ, Walker JE.; ''The nuclear encoded subunits of complex I from bovine heart mitochondria.''; PubMedEurope PMCScholia
Barros MH, Johnson A, Gin P, Marbois BN, Clarke CF, Tzagoloff A.; ''The Saccharomyces cerevisiae COQ10 gene encodes a START domain protein required for function of coenzyme Q in respiration.''; PubMedEurope PMCScholia
Balsa E, Marco R, Perales-Clemente E, Szklarczyk R, Calvo E, Landázuri MO, Enríquez JA.; ''NDUFA4 is a subunit of complex IV of the mammalian electron transport chain.''; PubMedEurope PMCScholia
Mitchell P.; ''Protonmotive redox mechanism of the cytochrome b-c1 complex in the respiratory chain: protonmotive ubiquinone cycle.''; PubMedEurope PMCScholia
Wikstrom MK.; ''Proton pump coupled to cytochrome c oxidase in mitochondria.''; PubMedEurope PMCScholia
Wood PA.; ''Defects in mitochondrial beta-oxidation of fatty acids.''; PubMedEurope PMCScholia
Loeffen J, Elpeleg O, Smeitink J, Smeets R, Stöckler-Ipsiroglu S, Mandel H, Sengers R, Trijbels F, van den Heuvel L.; ''Mutations in the complex I NDUFS2 gene of patients with cardiomyopathy and encephalomyopathy.''; PubMedEurope PMCScholia
Belogrudov GI, Hatefi Y.; ''Factor B and the mitochondrial ATP synthase complex.''; PubMedEurope PMCScholia
Sciacovelli M, Guzzo G, Morello V, Frezza C, Zheng L, Nannini N, Calabrese F, Laudiero G, Esposito F, Landriscina M, Defilippi P, Bernardi P, Rasola A.; ''The mitochondrial chaperone TRAP1 promotes neoplastic growth by inhibiting succinate dehydrogenase.''; PubMedEurope PMCScholia
Trumpower BL, Gennis RB.; ''Energy transduction by cytochrome complexes in mitochondrial and bacterial respiration: the enzymology of coupling electron transfer reactions to transmembrane proton translocation.''; PubMedEurope PMCScholia
Stiburek L, Hansikova H, Tesarova M, Cerna L, Zeman J.; ''Biogenesis of eukaryotic cytochrome c oxidase.''; PubMedEurope PMCScholia
Schultz BE, Chan SI.; ''Structures and proton-pumping strategies of mitochondrial respiratory enzymes.''; PubMedEurope PMCScholia
Garlid KD, Jaburek M, Jezek P.; ''Mechanism of uncoupling protein action.''; PubMedEurope PMCScholia
Belogrudov GI.; ''Factor B is essential for ATP synthesis by mitochondria.''; PubMedEurope PMCScholia
Roe CR, Roe DS.; ''Recent developments in the investigation of inherited metabolic disorders using cultured human cells.''; PubMedEurope PMCScholia
Loeffen JL, Triepels RH, van den Heuvel LP, Schuelke M, Buskens CA, Smeets RJ, Trijbels JM, Smeitink JA.; ''cDNA of eight nuclear encoded subunits of NADH:ubiquinone oxidoreductase: human complex I cDNA characterization completed.''; PubMedEurope PMCScholia
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Soto IC, Fontanesi F, Liu J, Barrientos A.; ''Biogenesis and assembly of eukaryotic cytochrome c oxidase catalytic core.''; PubMedEurope PMCScholia
Kevelam SH, Rodenburg RJ, Wolf NI, Ferreira P, Lunsing RJ, Nijtmans LG, Mitchell A, Arroyo HA, Rating D, Vanderver A, van Berkel CG, Abbink TE, Heutink P, van der Knaap MS.; ''NUBPL mutations in patients with complex I deficiency and a distinct MRI pattern.''; PubMedEurope PMCScholia
Schuelke M, Loeffen J, Mariman E, Smeitink J, van den Heuvel L.; ''Cloning of the human mitochondrial 51 kDa subunit (NDUFV1) reveals a 100% antisense homology of its 3'UTR with the 5'UTR of the gamma-interferon inducible protein (IP-30) precursor: is this a link between mitochondrial myopathy and inflammation?''; PubMedEurope PMCScholia
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Carilla-Latorre S, Gallardo ME, Annesley SJ, Calvo-Garrido J, Graña O, Accari SL, Smith PK, Valencia A, Garesse R, Fisher PR, Escalante R.; ''MidA is a putative methyltransferase that is required for mitochondrial complex I function.''; PubMedEurope PMCScholia
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In the tight configuration, the beta subunit catalyzes the reaction of ADP + Pi to ATP + water. ATP is still tightly bound to the subunit at this stage.
In the last step, the beta subunit is converted to the open form and ATP is released. Passage of protons through the Fo part causes a ring of approximately 10 subunits to rotate. This rotation in turn drives the rotation of the gamma subunits, which forms part of one of the stalks. The gamma subunit moves between the three beta subunits which are held in place by the second stalk which can be regarded as a stator. The polypeptide called OSCP connects the stator stalk to the assembly of alpha and beta subunits. It is this step that is coupled to proton translocation as energy is required to break the strong bond between ATP and the protein.
Complex IV (cytochrome oxidase) contains the hemeprotein cytochrome a and a3. It also contains copper atoms which undergo a transition from Cu+ to Cu2+ during the transfer of electrons through the complex to molecular oxygen. A bimetallic centre containing a copper atom and a heme-linked iron protein binds oxygen after 4 electrons have been picked up. Water, the final product of oxygen reduction, is then released. Oxygen is the final electron acceptor in the respiratory chain. The overall reaction can be summed as below: 4Cyt c(red.) + 12H+in + O2 -> 4Cyt c(ox.) + 2H2O + 8H+out
Four protons are taken up from the matrix side of the membrane to form the water (scalar protons). Wikstrom (1977) suggests 4 protons are additionally transferred out from the matrix to the intermembrane space.
At the beginning of this reaction, 1 molecule of 'Fatty Acid "head-out"' is present. At the end of this reaction, 1 molecule of 'Fatty Acid "head-in"' is present.
This reaction takes place in the 'mitochondrial inner membrane'.
Electron transfer flavoprotein, ETF, a 63kDa heterodimer composed of alpha and beta subunit, binds one FAD and one AMP per dimer. ETF resides on the matrix face of the mitochondrial inner membrane. Reducing equivalents from the beta-oxidation of fatty acyl CoAs are transferred to ETF, reducing the ETF-bound FAD to FADH2.
A FA anion diffuses laterally within the membrane towards UCP. The membrane potential drives the FA anion to an energy well halfway up on UCP. The electric field created by the redox-linked proton ejection drives the head group to the energy well.
At the beginning of this reaction, 1 molecule of 'H+', and 1 molecule of 'Fatty Acid anion "head-out"' are present. At the end of this reaction, 1 molecule of 'Fatty Acid "head-out"' is present.
This reaction takes place in the 'mitochondrial inner membrane'.
At the beginning of this reaction, 1 molecule of 'FA anion:UCP dimer "head-out" complex' is present. At the end of this reaction, 1 molecule of 'UCP dimer', and 1 molecule of 'Fatty Acid anion "head-out"' are present.
This reaction takes place in the 'mitochondrial inner membrane'.
The Protonmotive Q cycle is the mechanism by which complex III transfers electrons from ubiquinol to cytochrome c, linking this process to translocation of protons across the membrane. This cycle is complicated by the fact that both ubiquinol is oxidised and ubiquinone is reduced during this process. Through a complex series of electron transfers, Complex III consumes two molecules of ubiquinol (QH2) and two molecules of oxidized cytochrome c, generates one molecule of ubiquinone (Q) and two molecules of reduced cytochrome c, regenerates one molecule of ubiquinol (QH2), and mediates the translocation of two protons from the mitochondrial matrix to the mitochondrial intermembrane space.
The overall reaction can be summed up as below: 2QH2 + 2cyt c(ox.) + Q + 2H+matrix -> 2Q + 2cyt c(red.) + QH2 + 4H+memb. space
At the beginning of this reaction, 1 molecule of 'Fatty Acid "head-in"' is present. At the end of this reaction, 1 molecule of 'H+', and 1 molecule of 'Fatty Acid anion "head-in"' are present.
This reaction takes place in the 'mitochondrial inner membrane'.
Complex I (NADH:ubiquinone oxidoreductase or NADH dehydrogenase) utilizes NADH formed from glycolysis and the TCA cycle to pump protons out of the mitochondrial matrix. It is the largest enzyme complex in the electron transport chain, containing 45 subunits. Seven subunits (ND1-6, ND4L) are encoded by mitochondrial DNA (Loeffen et al [1998]), the remainder are encoded in the nucleus. The enzyme has a FMN prosthetic group and 8 Iron-Sulfur (Fe-S) clusters. The electrons from NADH oxidation pass through the flavin (FMN) and Fe-S clusters to ubiquinone (CoQ). This electron transfer is coupled with the translocation of protons from the mitochondrial matrix to the intermembrane space. For each electron transferred, 2 protons can be pumped out of the matrix. As there are 2 electrons transferred, 4 protons can be pumped out. Complex I is made up of 3 sub-complexes - Iron-Sulfur protein fraction (IP), Flavoprotein fraction (FP) and the Hydrophobic protein fraction (HP), probably arranged in an L-shaped structure with the IP and FP fractions protruding into the mitochondrial matrix and the HP arm lying within the inner mitochondrial membrane. The overall reaction can be summed as below: NADH + Ubiquinone + 5H+matrix ->NAD+ + Ubiquinol + 4H+memb. space
The electrons from complex I are transferred to ubiquinone (Coenzyme Q, CoQ), a small mobile carrier of electrons located within the inner membrane. Ubiquinone is reduced to ubiquinol during this process.
This event is deduced on the basis of bovine experimental data. Complex II (succinate dehydrogenase) transfers electrons from the TCA cycle to ubiquinone. The 6th step in the TCA cycle is where succinate is dehydrogenated to fumarate with subsequent reduction of FAD to FADH2. FADH2 provides the electrons for the transport chain. Succinate dehydrogenase belongs to subclass 1 of the SQR family (succinate:quinone reductase) (classified by Hagerhall, C and Hederstedt, L [1996]). It consists of 4 subunits (referred to as A, B, C and D), all nuclear-encoded and is located on the matrix side of the inner mitochondrial membrane. Subunits A and B are hydrophilic whereas subunits C and D are integral proteins of the inner membrane. SQRs usually contain 3 Fe-S clusters bound by the B subunit. Succinate dehydrogenase contains one [2Fe-2S] cluster, one [4Fe-4S] cluster and one [3Fe-4S] cluster. Additionally, the A subunit has a covalently-bound FAD group. Reduced complex II has this FAD converted to FADH2. The electrons from complex II are transferred to ubiquinone (also called Q, Coenzyme Q or CoQ), a small mobile carrier of electrons located within the inner membrane. Ubiquinone is reduced to ubiquinol during this process.
The beta subunit has 3 conformations; tight, open and loose. ADP and Pi bind to the subunit in the loose form. On binding, this subunit is converted to the tight configuration.
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4Cyt c(red.) + 12H+in + O2 -> 4Cyt c(ox.) + 2H2O + 8H+out
Four protons are taken up from the matrix side of the membrane to form the water (scalar protons). Wikstrom (1977) suggests 4 protons are additionally transferred out from the matrix to the intermembrane space.
This reaction takes place in the 'mitochondrial inner membrane'.
This reaction takes place in the 'mitochondrial inner membrane'.
This reaction takes place in the 'mitochondrial inner membrane'.
The overall reaction can be summed up as below:
2QH2 + 2cyt c(ox.) + Q + 2H+matrix -> 2Q + 2cyt c(red.) + QH2 + 4H+memb. space
This reaction takes place in the 'mitochondrial inner membrane'.
Complex I is made up of 3 sub-complexes - Iron-Sulfur protein fraction (IP), Flavoprotein fraction (FP) and the Hydrophobic protein fraction (HP), probably arranged in an L-shaped structure with the IP and FP fractions protruding into the mitochondrial matrix and the HP arm lying within the inner mitochondrial membrane. The overall reaction can be summed as below:
NADH + Ubiquinone + 5H+matrix -> NAD+ + Ubiquinol + 4H+memb. space
The electrons from complex I are transferred to ubiquinone (Coenzyme Q, CoQ), a small mobile carrier of electrons located within the inner membrane. Ubiquinone is reduced to ubiquinol during this process.
This reaction takes place in the 'mitochondrial inner membrane' and is mediated by the 'hydrogen ion transporter activity' of 'UCP dimer'.
Complex II (succinate dehydrogenase) transfers electrons from the TCA cycle to ubiquinone. The 6th step in the TCA cycle is where succinate is dehydrogenated to fumarate with subsequent reduction of FAD to FADH2. FADH2 provides the electrons for the transport chain. Succinate dehydrogenase belongs to subclass 1 of the SQR family (succinate:quinone reductase) (classified by Hagerhall, C and Hederstedt, L [1996]).
It consists of 4 subunits (referred to as A, B, C and D), all nuclear-encoded and is located on the matrix side of the inner mitochondrial membrane. Subunits A and B are hydrophilic whereas subunits C and D are integral proteins of the inner membrane. SQRs usually contain 3 Fe-S clusters bound by the B subunit. Succinate dehydrogenase contains one [2Fe-2S] cluster, one [4Fe-4S] cluster and one [3Fe-4S] cluster. Additionally, the A subunit has a covalently-bound FAD group. Reduced complex II has this FAD converted to FADH2. The electrons from complex II are transferred to ubiquinone (also called Q, Coenzyme Q or CoQ), a small mobile carrier of electrons located within the inner membrane. Ubiquinone is reduced to ubiquinol during this process.