Cytochrome c Oxidase
This chapter emphasizes the importance of cytochrome c oxidase as one of the major copper enzymes in nature. The term "cytochrome oxidase" was introduced by Dixon in 1929. Cytochrome c oxidase is a mitochondrial transmembrane protein and thus tightly associated with the phospholipids of the inner mitochondrial membrane. The oxidase contains two functionally different heme a and copper moieties. The number of heme a and copper binding subunits therefore can maximally be four and is likely smaller if hemes a and/or coppers occur together in one subunit. While the number and stoichiometry of mitochondrial subunits of the oxidase is well-defined, considerable uncertainty exists with the protein components synthesized on cytoplasmic ribosomes and, most probably, coded by the nucleus. Besides the necessity to analyse the primary structure of cytochrome c oxidase, determination of the three-dimensional structure of the enzyme is the major task for an improved understanding of the molecule.