A proton pump is an integral membrane protein that is capable of moving protons across the membrane of a cell, mitochondrion, or other subcellular compartment, thereby creating a difference or gradient in both pH and electrical charge (ignoring differences in buffer capacity) and tending to establish an electrochemical potential.
In bacteria, mitochondria and other ATP-producing organelles, reducing equivalents provided by electron transfer or photosynthesis power this translocation of protons. For example, the translocation of protons by cytochrome c oxidase is powered by reducing equivalents provided by reduced cytochrome c. In the plasma membrane proton ATPase and in the ATPase proton pumps of other cellular membranes, ATP itself powers this transport.
The F0F1 ATP synthase of mitochondria and the CF1 ATP synthetase of chloroplasts, in contrast, usually conduct protons from high to low concentration across the membrane while drawing energy from this flow to synthesize ATP.
Bacteriorhodopsin is a photosynthetic pigment used by archaea, most notably halobacteria.