Studies on CytochromecOxidase, XII. Isolation and Primary Structure of Polypeptide VIb from Bovine Heart

Abstract

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.