Subunit I and II form the functional core of the enzyme complex. Electrons originating in cytochrome c are transferred via heme a and Cu(A) to the binuclear center formed by heme a3 and Cu(B). This cytochrome c oxidase shows proton pump activity across the membrane in addition to the electron transfer. 4 Fe(II)-[cytochrome c] + 8 H(+)(in) + O2 = 4 Fe(III)-[cytochrome c] + 4 H(+)(out) + 2 H2O Binds 1 copper B ion per subunit. Binds 2 heme groups per subunit. Energy metabolism; oxidative phosphorylation. His-276 and Tyr-280 are involved in the formation of a copper-coordinated covalent cross-link at the active site of the catalytic subunit I. Belongs to the heme-copper respiratory oxidase family.