Electron bifurcation, cytochrome

FIGURE 2. Q-cycle schematic diagram. Two ubiquinol molecules need to be oxidized at the Qo site to fully reduce one ubiquinone molecule at Qj site. The quinone oxidation reaction at Qo site is bifurcated with electron passed dirough two separate chains the high potential chain of Rieske protein and cytochrome c, and the low potential chain of haem bL and haem bn-The abbreviations are defined in die text. 

Figure 1 The mitochondrial respiratory chain. Electron transfer (brown arrows) between the three major membrane-bound complexes (I, III, and IV) is mediated by ubiquinone (Q/QH2) and the peripheral protein c)dochrome c (c). Transfer of protons hnked to the redox chemistry is shown by blue arrows red arrows denote proton translocation. NAD+ nicotinamide adenine dinucleotide, FMN flavin mononucleotide, Fe/S iron-sulfur center bH,bi, and c are the heme centers in the cytochrome bc complex (Complex III). Note the bifurcation of the electron transfer path on oxidation of QH2 by the heme bL - Fe/S center. Complex IV is the subject of this review. N and P denote the negatively and positively charged sides of the membrane, respectively...

Now that it is substantiated that the [2Fe 2S] domain of the Rieske iron-sulfur protein is not static but moves between domains of cytochrome-c, and cytochrome-/ subunits, and that it is likely that such movement may provide a novel mechanism to allow catalysis of all the reactions involved in the oxidation of hydroquinone at the Qo site and the subsequent bifurcated pathway of electron transfer. It has been found that during the movement, the mobile [2Fe 2S] domain retains essentially the same tertiary structure, and the anchoring N-terminal tail of the R-ISP molecule remains in the same fixed position. The movement occurs through an extension of a helical segment in the short linking span. 

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