cytochrome-c oxidase activity Catalysis of the reaction: 4 ferrocytochrome c + O2 + 4 H+ = 4 ferricytochrome c + 2 H2O. EC:1.9.3.1 GO:0004129 MetaCyc:CYTOCHROME-C-OXIDASE-RXN NADH cytochrome c oxidase Reactome:REACT_113276 Reactome:REACT_113311 Reactome:REACT_113736 Reactome:REACT_115027 Reactome:REACT_33608 Reactome:REACT_6149 Reactome:REACT_78871 Reactome:REACT_99789 The reduction of O2 to water is accompanied by the extrusion of four protons from the intramitochondrial compartment. aa3-type cytochrome c oxidase ba3-type cytochrome c oxidase caa3-type cytochrome c oxidase cbb3-type cytochrome c oxidase complex IV (mitochondrial electron transport) activity cytochrome a3 activity cytochrome aa3 activity cytochrome c oxidase activity cytochrome oxidase activity ferrocytochrome c oxidase ferrocytochrome-c:oxygen oxidoreductase indophenol oxidase indophenolase molecular_function warburg's respiratory enzyme activity electron carrier activity