Amino acid sequence of the heme a subunit of bovine heart cytochrome oxidase and sequence homology with hemoglobin

The amino acid sequence of the 11.6 K dalton heme a subunit of bovine heart cytochrome oxidase has been completed and is presented here. The sequence investigation has established the positions in the protein of all the possible heme ligands, namely cysteine, methionine, histidine and lysine residues. However, the isolation conditions may have caused the heme a to migrate from its original site or the heme is caged by peptides as pointed out in Reference 6. The sequence of the heme a subunit and the β-chain of hemoglobin shows homology. It is possible that these two proteins have arisen from a common ancestor in the distant past.