Conformational Dependence of Carbon Monoxide Ligation Dynamics in Cytochrome c Oxidase

Time-resolved optical studies have recently demonstrated that ligand photolysis and rebinding in fully reduced cytochrome c oxidase (Cco) is an extremely complicated process involving structural dynamics of both the proximal and distal heme pockets of cytochrome a₃. We have expanded upon these studies by examining the corresponding ligation dynamics in mixed-valence (MV) Cco, which is known to exist in a conformation that is structurally and kinetically distinct from fully reduced (FR) Cco. We report here time-resolved Raman results showing that while the promximal heme pocket dynamics of MV-Cco are similar to those of FR-Cco, the ligation dynamics of the distal pocket are affected by the protein conformational state.