title: Is redox-cycling ubiquinone involved in mitochondrial oxygen activation?
abstract: In most tissues mitochondria consume more than 90% of cellular oxygen. Although the greatest part of it undergoes tetravalent reduction thereby conserving free energy changes in the form of ATP, a great deal of evidence exists in the literature that also univalently reduced dioxygen is released during respiration. Redox-cycling ubiquinone was considered most frequently to be involved in this univalent e- transfer to oxygen out of sequence however, other components of the respiratory chain could not be excluded. Our investigations on this problem questioned the role of redox-cycling ubiquinone in mitochondrial O2- formation while H2O2 is supposed to accept e- from this source. The paper provides experimental evidence that H2O2 in fact may operate as an oxidant of ubisemiquinone while dioxygen requires protons for such a reaction which are not available in the phospholipid bilayer where ubiquinone undergoes one e- redox-cycling.
authors.affiliation: Institute of Pharmacology and Toxicology, Veterinary University of Vienna, Austria.
authors.forename: H
authors.initials: H
authors.lastname: Nohl
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D003573:Cytochrome b Group / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D005609:Free Radicals; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007700:Kinetics; D008928:Mitochondria / Q000378:metabolism*; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D013482:Superoxide Dismutase / Q000378:metabolism; D014451:Ubiquinone / Q000378:metabolism*
chemical_list: D003573:Cytochrome b Group; D005609:Free Radicals; D014451:Ubiquinone; D000255:Adenosine Triphosphate; D006861:Hydrogen Peroxide; D013482:Superoxide Dismutase