Coenzyme Q – cytochrome c reductase

About: Coenzyme Q – cytochrome c reductase is a research topic. Over the lifetime, 4663 publications have been published within this topic receiving 244853 citations. The topic is also known as: mitochondrial respiratory chain complex III & respiratory chain complex III.

How mitochondria produce reactive oxygen species.

Abstract: The production of ROS (reactive oxygen species) by mammalian mitochondria is important because it underlies oxidative damage in many pathologies and contributes to retrograde redox signalling from the organelle to the cytosol and nucleus. Superoxide (O2•−) is the proximal mitochondrial ROS, and in the present review I outline the principles that govern O2•− production within the matrix of mammalian mitochondria. The flux of O2•− is related to the concentration of potential electron donors, the local concentration of O2 and the second-order rate constants for the reactions between them. Two modes of operation by isolated mitochondria result in significant O2•− production, predominantly from complex I: (i) when the mitochondria are not making ATP and consequently have a high Δp (protonmotive force) and a reduced CoQ (coenzyme Q) pool; and (ii) when there is a high NADH/NAD+ ratio in the mitochondrial matrix. For mitochondria that are actively making ATP, and consequently have a lower Δp and NADH/NAD+ ratio, the extent of O2•− production is far lower. The generation of O2•− within the mitochondrial matrix depends critically on Δp, the NADH/NAD+ and CoQH2/CoQ ratios and the local O2 concentration, which are all highly variable and difficult to measure in vivo. Consequently, it is not possible to estimate O2•− generation by mitochondria in vivo from O2•−-production rates by isolated mitochondria, and such extrapolations in the literature are misleading. Even so, the description outlined here facilitates the understanding of factors that favour mitochondrial ROS production. There is a clear need to develop better methods to measure mitochondrial O2•− and H2O2 formation in vivo, as uncertainty about these values hampers studies on the role of mitochondrial ROS in pathological oxidative damage and redox signalling.

The mitochondrial electron transport and oxidative phosphorylation system

Abstract: NADH:UBIQUINONE OXIDOREDUCTASE (COMPLEX I) . . ....... .. .... . . . . . . . . . . . . . . . . 1019 Compositio,� of Complex I 1019 Light Absorption and ESR Spectral Properties of Complex I . ... ......... 1020 Structure of Complex I 1022 Catalytic Properties and Mechanism of Action of Complex I 1022 SUCCINATE:UBIQUINONE OXIDOREDUCTASE (COMPLEX II) . . . . . . . . . . . . . . . . . . . . . . 1024 Compositio.� and Structure of Complex II .. .... .. ... . . ..... . . . . . . . . 1025 Light AbsOlption and ESR Spectral Properties of Complex II and SDH. . . . . . . . . . . . . . . . 1026 Catalytic Properties and Mechanism of Action of Complex II and SDH .... . . . ........ 1027 UBIQUINOL:CYTOCHROME c OXIDOREDUCTASE (COMPLEX III) . . . . . . . . . . . . . . . . . 1030 Composition and Structure of Complex III ..... . . . 1030 Catalytic Properties and Mechanism of Action of Complex III 1034 FERROCYTOCHROME c:OXYGEN OXIDOREDUCTASE (COMPLEX IV) . . . . . . . . . . . 1038 Polypeptide Composition and Structure of Cytochrome c Oxidase . . . . . . . . . . . . . . . . . . . . . . 1038 Prosthetic Groups of Cytochrome c Oxidase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1042 Catalytic Properties and Mechanism of Action of Cytochrome c Oxidase . . . . . . . . . . . . . . 1045 ATP SYNTHASE (COMPLEX V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1048 Composition and Structure of ATP Synthase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1048 Catalytic Properties of ATP Synthase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1053 Mechanism Of ATP Hydrolysis and Synthesis .. . . . . . . . . . . . . . . . . . . . ... .. . . . . . . . . . . . . . . . . . . . . . . 1054

PLANT MITOCHONDRIA AND OXIDATIVE STRESS: Electron Transport, NADPH Turnover, and Metabolism of Reactive Oxygen Species.

Abstract: The production of reactive oxygen species (ROS), such as O2- and H2O2, is an unavoidable consequence of aerobic metabolism. In plant cells the mitochondrial electron transport chain (ETC) is a major site of ROS production. In addition to complexes I-IV, the plant mitochondrial ETC contains a non-proton-pumping alternative oxidase as well as two rotenone-insensitive, non-proton-pumping NAD(P)H dehydrogenases on each side of the inner membrane: NDex on the outer surface and NDin on the inner surface. Because of their dependence on Ca2+, the two NDex may be active only when the plant cell is stressed. Complex I is the main enzyme oxidizing NADH under normal conditions and is also a major site of ROS production, together with complex III. The alternative oxidase and possibly NDin(NADH) function to limit mitochondrial ROS production by keeping the ETC relatively oxidized. Several enzymes are found in the matrix that, together with small antioxidants such as glutathione, help remove ROS. The antioxidants are kept in a reduced state by matrix NADPH produced by NADP-isocitrate dehydrogenase and non-proton-pumping transhydrogenase activities. When these defenses are overwhelmed, as occurs during both biotic and abiotic stress, the mitochondria are damaged by oxidative stress.