The structure of Wolinella succinogenes quinol:fumarate reductase and its relevance to the superfamily of succinate:quinone oxidoreductases

The chapter gives an overview of current status of discussion of electron and proton transfer in succinate: quinone oxidoreductases. In mitochondrial complex II and other C-type enzymes, such as SQR from P denitrificans and E. coli, electron transfer from succinate to ubiquinone does not lead to the generation of a transmembrane electrochemical potential Δp, since the protons released by succinate oxidation are on the same side of the membrane as those consumed by quinone reduction. It is unlikely that transmembrane electron transfer occurs in the E. coli quinol: fumarate reductases (QFR), because of the large edge-to-edge distance of ∼25 Å between the two quinone models. Therefore, it is most likely that quinol oxidation occurs at a proximal site