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 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

Key Words:

• Mitochondria
• ubisemiquinone
• cytochrome b
• superoxide radicals
• hydroxyl radicals.