Component of the cytochrome c oxidase, the last enzyme in the mitochondrial electron transport chain which drives oxidative phosphorylation. The respiratory chain contains 3 multisubunit complexes succinate dehydrogenase (complex II, CII), ubiquinol-cytochrome c oxidoreductase (cytochrome b-c1 complex, complex III, CIII) and cytochrome c oxidase (complex IV, CIV), that cooperate to transfer electrons derived from NADH and succinate to molecular oxygen, creating an electrochemical gradient over the inner membrane that drives transmembrane transport and the ATP synthase. Cytochrome c oxidase is the component of the respiratory chain that catalyzes the reduction of oxygen to water. Electrons originating from reduced cytochrome c in the intermembrane space (IMS) are transferred via the dinuclear copper A center (CU(A)) of subunit 2 and heme A of subunit 1 to the active site in subunit 1, a binuclear center (BNC) formed by heme A3 and copper B (CU(B)). The BNC reduces molecular oxygen to 2 water molecules using 4 electrons from cytochrome c in the IMS and 4 protons from the mitochondrial matrix. Energy metabolism; oxidative phosphorylation. Component of the cytochrome c oxidase (complex IV, CIV), a multisubunit enzyme composed of a catalytic core of 3 subunits and several supernumerary subunits. The complex exists as a monomer or a dimer and forms supercomplexes (SCs) in the inner mitochondrial membrane with ubiquinol-cytochrome c oxidoreductase (cytochrome b-c1 complex, complex III, CIII). Belongs to the cytochrome c oxidase VIIa family.