Redox-driven membrane-bound proton pumps

In recent years, remarkable progress has been made in our understanding of the structure and function of membrane-bound proton transporters at the molecular level. Perhaps the most challenging and complex of these molecular machines are the haem–copper oxidases. These enzymes are designed to activate the kinetically stable O 2 molecule, to prevent the release of potentially toxic oxygen intermediates and, at the same time, to harness the free energy from O 2 reduction by pumping protons across the membrane. So far, the mechanism of proton pumping has not been determined in any proton pump driven by reduction–oxidation reactions. Although this remains one of the key problems of molecular bioenergetics, recent developments have brought us to its core and closer to its solution.