Cytochrome c oxidase is the component of the respiratory chain that catalyzes the reduction of oxygen to water. Subunits 1-3 form the functional core of the enzyme complex. Co I is the catalytic subunit of the enzyme. Electrons originating in cytochrome c or a quinol are transferred to the bimetallic center formed by a high-spin heme and copper B. 4 Fe(II)-[cytochrome c] + 8 H(+)(in) + O2 = 4 Fe(III)-[cytochrome c] + 4 H(+)(out) + 2 H2O Binds 1 copper ion per subunit, denoted as copper B. Binds 2 heme b groups per subunit, denoted as high- and low-spin. Energy metabolism; oxidative phosphorylation. Belongs to the heme-copper respiratory oxidase family.