The enzyme cytochrome c oxidase or Complex IV, EC 1.9.3.1, is a large transmembrane protein complex found in bacteria, archaea, and the mitochondria of eukaryotes.It is the last enzyme in the respiratory electron transport chain of cells located in the membrane. It receives an electron from each of four cytochrome c molecules, and transfers them to one dioxygen molecule, converting the molecular oxygen to two molecules of water. [Source: Wikipedia 
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