 One such example is blockage of ATP production by ATP synthase, resulting in a build-up of protons and therefore a higher proton-motive force, inducing reverse electron flow.In eukaryotes, NADH is the most important electron donor.The associated electron transport chain is

NADH → "Complex I" → Q → "Complex III" → cytochrome "c" → "Complex IV" → O2
where "Complexes I, III" and" IV" are proton pumps, while Q and cytochrome "c" are mobile electron carriers.