cythocrome c oxidase
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 CuA centre and a mononuclear CuB centre coupled to one of the hemes).
Cytochrome c transfers one electron to the
CuA centre. This electron afterwards moves to a
heme a , and thence to
heme aa3, which is coupled to CuB. Together, this heme and CuB 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. Complex IV can be inhibited by cyanide. CN- competitively binds to heme aa3 and prevents electron flow from cytochrome c to the oxygen molecule.