ATP Synthesis: Mitochondrial Cyanide-Resistant Terminal Oxidases
© 2013 Elsevier Inc. All rights reserved. Mitochondria from all eukaryotic organisms contain cytochrome c oxidase as the standard terminal oxidase that serves to transport electrons to oxygen, the terminal electron acceptor in the process of aerobic respiration, and brings about the four-electron reduction of oxygen to produce two molecules of water. However, many organisms also contain a second terminal oxidase in their mitochondrial electron transfer chain in addition to cytochrome c oxidase. Functionally, this alternative oxidase is a ubiquinol oxidase, receiving electrons from reduced ubiquinone and transferring them to oxygen, which is reduced to water. Electron flow from reduced ubiquinone to cytochrome c oxidase includes two sites for transporting protons across the inner mitochondrial membrane to form a proton gradient across the membrane that drives adenosine triphosphate (ATP) formation. Electron flow through the alternative oxidase involves no proton translocation and therefore wastes all the free energy released during electron transfer that would otherwise be conserved in the proton gradient to produce ATP. The role of such an energetically wasteful pathway has yet to be fully elucidated; however, in plants it appears to be associated with response to a variety of stresses, possibly acting to prevent over-reduction of the quinone pool and the subsequent formation of harmful reactive oxygen species.
- Encyclopedia of Biological Chemistry: Second Edition
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International Standard Book Number 13 (ISBN-13)
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