The quinone chemistry of bc complexes

The quinone chemistry that gives rise to the rather unusual strict bifurcation of electron transfer at the Q(o) site of the cytochrome bc complexes remains controversial. In this article, I review recent ideas and propose a "logic-gated" binding mechanism that combines classical quinone electrochemistry with specific hydrogen bonding requirements and results in a reversible reaction that minimizes unwanted side-reactions that could otherwise undermine the efficiency of the Q-cycle proton/electron coupling mechanism.