Cytochrome oxidase is a biological system that is chemically fascinating because it catalyzes a complex reaction, the reduction of molecular oxygen to water, and physiologically essential because this thermodynamically energy-producing reaction is coupled to the production of a chemical fuel, ATP, in large quantities. Despite the thermodynamically favorable nature of the reaction, oxygen reduction is complex, as it involves the transfer of 4 electrons and therefore requires a catalyst. Moreover, the coupling with ATP synthesis is not direct, but involves the coupling of redox reactions with the formation of pH gradients across the membrane, so that cytochrome oxidase is not only an electron transfer system, but also a proton pump.
The lecture introduced the thermodynamics of the reaction, the chemo-osmotic theory and the notion of proton motive force, the structures of cytochrome oxidase and more particularly its metallic oxygen reduction site, a binuclear site consisting of an iron porphyrin (cytochrome) and a copper complex. This enabled us to discuss the mechanisms of electron transfer and proton transfer, which are still highly controversial and actively developed research topics.
