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 oxida se isolated from thermophilic Bacillus PS3, we developed a simple proc edure including chemical cross-linking, two consecutive runs of electr ophoresis, proteolytic digestion, and peptide sequencing for simultane ous identification of two cross-linked fragments. By this procedure, t he cytochrome c domain of subunit 2 was found cross-linked to C-termin al region of subunit 1 including two hydrophobic transmembrane segment s, suggesting that these two regions were located close each other. Th e present simple procedure might be applicable to proteins whose cryst al structures are not revealed.