Identification of peptide fragments chemically cross-linked in cytochrome c oxidase from thermophilic Bacillus PS3.

In order to study steric arrangement of subunits in cytochrome c oxidase isolated from thermophilic Bacillus PS3, we developed a simple procedure including chemical cross-linking, two consecutive runs of electrophoresis, proteolytic digestion, and peptide sequencing for simultaneous identification of two cross-linked fragments. By this procedure, the cytochrome c domain of subunit 2 was found cross-linked to C-terminal region of subunit 1 including two hydrophobic transmembrane segments, suggesting that these two regions were located close each other. The present simple procedure might be applicable to proteins whose crystal structures are not revealed.