Figure 3

Supply, demand and leak pathways of the protonmotive force in mitochondria. Redox reactions at the respiratory complexes (I to IV) create a proton electrochemical gradient, which may be consumed by the F_o/F₁ ATPase to produce ATP or by proton leak pathways, which release energy in the form of heat. Proton leak pathways can occur through gradient-dependent cycling for example by fatty acids (FAs) or by activation of uncoupling protein (UCP). FA, fatty acid, UCP, uncoupling protein.