Studies on Cytochrome-c Oxidase, XIV. The Amino-acid Sequence of Subunit I--proteinchemical Methods for the Analysis of a Large Hydrophobic Membrane Protein

The amino-acid sequence of bovine heart cytochrome-c oxidase subunit I, previously deduced from mtDNA was corroborated by proteinchemical methods. The protein consists of 514 amino acids, the Mr is 57,060 including the N-terminal formyl group, which is positively identified. The study describes methods for the purification of the hydrophobic polypeptide by BioGel-chromatography in 3% SDS and/or HPLC and the sequence analysis via complete peptide maps obtained either by chymotryptic or cyanogenbromide cleavage in the presence of residual amounts of SDS. The methods may be used either for a stand alone sequencing of large integral membrane proteins or for obtaining probes to find the gene and provide the necessary complement for DNA sequencing. The results present the only protein-derived evidence for a family of about 20 DNA-deduced sequences of the catalytic subunit of cytochrome oxidases from bacteria to man.