Abstract

Low-power picosecond resonance Raman spectroscopy was used to investigate the identity of the axial ligand of heme a₃ and relaxation processes in the heme a₃ pocket of cytochrome oxidase after CO photolysis. Our results show that the proximal histidine remains ligated to heme a₃ after CO photolysis excluding the transient ligation of a photolabile, endogenous ligand. Furthermore, the relaxation of the heme a₃ macrocycle modes occurs on the sub ps time scale, while relaxation of the heme pocket to its equilibrium conformation takes place on the μs time scale.