Free Radical Production by the Mitochondrion
The electron transport chain located in the mitochondrial inner membrane catalyzes the complete oxidation of NADH to water. This reaction is carried out by a complex system which involves the sequential participation of more than thirty redox-active components including flavoproteins (dehydrogenases), iron-sulfur proteins (dehydrogenases, Rieske protein, etc.), hemecontaining proteins (cytochromes), and a lipid (ubiquinone). Some of these components carry only one electron at a time (cytochromes of the b and c type), while others transport two (flavoproteins) and four (cytochrome oxidase) electrons in a single step. As a consequence, there are several points in the chain in which a two-electron carrier must reduce a one-electron carrier, producing free radical intermediates. One of them, ubisemiquinone, is present in relatively large amounts in the respiring respiratory chain, and may be detected by electron spin resonance.
KeywordsElectron Spin Resonance Respiratory Chain Xanthine Oxidase Mitochondrial Respiratory Chain NADH Dehydrogenase
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