A fourth subunit is present in cytochrome c oxidase from the thermophilic bacterium PS3

A new putative subunit was found in cytochrome c oxidase (aa3-type) of the thermophilic bacterium PS3. The N-terminal amino acid sequence of this approximately 12 kDa protein coincides with the deduced sequence of an open reading frame found downstream from the gene encoding subunit I of the PS3 cytochrome oxidase [(1988) J. Biochem. 103, 606-610]. This small hydrophobic protein, composed of 109 amino acid residues after the initial methionine residue has been processed, shows homology with the subunit IV (cyoD product) of cytochrome bo-type quinol oxidase of Escherichia coli.