NADH possesses lots of energy. In E. coli , can have two different terminal oxidases, one functions at high oxygen levels, one at lower oxygen levels. Membrane is basically impermeable to protons, so gradient doesn't get squandered away by leaky reentry. ATP synthase protein complex contains only channels for proton entry. Proton gradient develops across inner mitochondrial membrane.
Mitochondria are very efficient at generating proton gradient.
Proton gradient develops across this membrane. Bacteria are not as efficient. Inhibitors of Oxidative Phosphorylation Several chemicals can block electron transfer in ETS, or transfer of electrons to oxygen. All are strong poisons. Most common in bacteria.