1AR1 -cytochrome c oxidase.
Ostermeier, Harrenga, Ermler and Michel (1997) Proc. Natl. Acad. Sci. USA, 94:10547

Complex IV (cytochrome c oxidase) accepts electrons from cytochrome c and transfers them to an oxygen molecule, thereby reducing it to H₂O. In order to perform this electron transfer, complex IV contains two heme groups and three Cu atoms (distributed between a binuclear Cu_A centre and a mononuclear Cu_B centre coupled to one of the hemes). Cytochrome c transfers one electron to the
Cu_A centre. This electron afterwards moves to a
heme a , and thence to
heme aa₃, which is coupled to Cu_B. Together, this heme and Cu_B transfer four electrons to O₂ and reduce it to water. The protons required for this reaction come from the mytochondrial matrix. As in complex I and complex III, the electron transfer lowers H⁺ concentration in the matrix relative to the intermembrane space.