Is Redox-Cycling Ubiquinone Involved In Mitochondrial Oxygen Activation?

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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 O−2 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