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 Cox2 and heme A of Cox1 to the active site in Cox1, 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 11 subunits. The complex is composed of a catalytic core of 3 subunits Cox1, Cox2 and Cox3, encoded in the mitochondrial DNA, and 8 supernumerary subunits Cox4, Cox5a/Cox5, Cox6, Cox7, Cox8, Cox7a/Cox9, Cox6b/Cox12 and Cox6a/Cox13, which are encoded in the nuclear genome (PubMed:31316820). The complex exists as a monomer or a dimer and forms respiratory supercomplexes (SCs) in the inner mitochondrial membrane with NADH-ubiquinone oxidoreductase (complex I, CI) and ubiquinol-cytochrome c oxidoreductase (cytochrome b-c1 complex, complex III, CIII), resulting in various different assemblies (supercomplexes I(1)IV(1), I(1)III(3)IV(2), III(2)IV(1) and III(2)IV(2) as well as larger supercomplexes of compositions like I(1)III(2)IV(5-6)) (PubMed:17873079). Belongs to the cytochrome c oxidase VIIa family.