Electron transfer
Electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-Q oxidoreductase), also known as "electron transferring-flavoprotein dehydrogenase", is a third entry point to the electron transport chain. It is an enzyme that accepts electrons from electron-transferring flavoprotein in the mitochondrial matrix, and uses these electrons to reduce ubiquinone. This enzyme contains a flavin and a [4Fe–4S] cluster, but, unlike the other respiratory complexes, it attaches to the surface of the membrane and does not cross the lipid bilayer.