The Role of Quinones in the Mitochondrial Electron Transport System

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Abstract
Two quinones, α-tocopherol and coenzyme Q are present in high concentration in mitochondria isolated from mammalian tissues; however, only coenzyme Q has been shown to undergo oxidation and reduction during electron transport. Coenzyme Q functions as an intermediate electron carrier between the flavoprotein and cytochrome regions of the terminal electron transport system. Coenzyme Q does not, however, react directly with the flavoproteins and evidence obtained from studies on the isolated succinic coenzyme Q reductase suggests that an additional redox component is required to mediate the transfer of electrons from the flavoprotein to coenzyme Q. This component has not been thoroughly characterized but the preliminary studies indicate that it is an iron-containing compound (nonheme) in which the iron undergoes cyclic oxidation and reduction during the oxidation of succinate by coenzyme Q.