Editing Electron transport chain (section)

=== Proton pumps ===
A ''[[proton pump]]'' is any process that creates a [[proton gradient]] across a membrane. Protons can be physically moved across a membrane, as seen in mitochondrial ''Complexes I'' and ''IV''. The same effect can be produced by moving electrons in the opposite direction. The result is the disappearance of a proton from the cytoplasm and the appearance of a proton in the periplasm. Mitochondrial ''Complex III'' is this second type of proton pump, which is mediated by a quinone (the [[Q cycle]]).

Some dehydrogenases are proton pumps, while others are not. Most oxidases and reductases are proton pumps, but some are not. Cytochrome ''bc<sub>1</sub>'' is a proton pump found in many, but not all, bacteria (not in ''E. coli''). As the name implies, bacterial ''bc<sub>1</sub>'' is similar to mitochondrial ''bc<sub>1</sub>'' (''Complex III'').