Fig. 1

Oxidative Phosphorylation System (OXPHOS). Electrons derived from cellular metabolism reach complex I or complex II through NADH or FADH2, respectively. These electrons are then transferred to coenzyme Q (ubiquinone), a carrier of electrons from complex I or II, to III. In the latter, particles are shifted form cytochrome b to cytochrome c with a consequent transfer to Complex IV (cytochrome oxidase) where they reduce O2. This electrons transport through mitochondrial complexes is coupled to shipment of protons in the intermembrane space. The electrochemical gradient generated is used by Complex V for ATP synthesis. Adapted from the KEGG Oxidative phosphorylation pathway (Reference number: 00190, http://www.genome.jp/kegg-bin/show_pathway?map00190)