CO photolysis of cytochrome oxidase investigated by PS resonance Raman spectroscopy

Low-power picosecond resonance Raman spectroscopy was used to investigate t he identity of the axial ligand of heme a(3) and relaxation processes in th e heme a(3) pocket of cytochroms oxidase after CO photolysis. Our results s how that the proximal histidine remains ligated to heme a(3) after CO photo lysis excluding the transient ligation of a photolabile, endogenous ligand. Furthermore, the relaxation of the heme a(3) macrocycle modes occurs on th e sub ps time scale, while relaxation of the heme pocket to its equilibrium conformation takes place on the mu s time scale.