Studies on cytochrome c oxidase, XII. Isolation and primary structure of polypeptide VIb from bovine heart.

The isolation and complete sequence analysis of the cytoplasmically synthesized polypeptide VIb from bovine heart cytochrome c oxidase is described. The protein is a stoichiometric constituent of the respiratory complex IV. Its primary structure is deduced from N-terminal sequencing and overlapping peptides obtained from tryptic cleavage and specific cleavage at arginyl and tryptophyl peptide bonds. The polypeptide chain consists of 84 amino acids from which a Mr of 9419 is derived. It has a relatively high content of histidine and proline and contains a single cysteine. A hydrophobic sequence of 20 amino acids points to a membrane-penetrating structure similar to that found in polypeptides I, II, III, IV and VIIIa, VIIIb, VIIIc of the bovine oxidase. The sequence of VIb is tissue-specific, it contributes to the formation of nuclear coded isoenzymes of cytochrome c oxidase. The protein thus may be involved in a tissue-specific regulation of cellular respiration.