Q Cycle

Q Cycle

The Q cycle describes a series of reactions first proposed by Peter Mitchell that describe how the sequential oxidation and reduction of the lipophilic electron carrier, ubiquinol-ubiquinone (a.k.a. Coenzyme Q), can result in the net pumping of protons across a lipid bilayer (in the case of mitochondria, the inner mitochondrial membrane). A modified version of Mitchell's original scheme is now accepted as the mechanism by which Complex III pumps protons (i.e. how complex III contributes to the biochemical generation of the proton or pH, gradient, which is used for the biochemical generation of ATP).