An Intermediate Conformational State during Ligand Binding to Cytochrome c Oxidase Detected by Time-resolved Resonance Raman Analyses of Heme Peripheral Groups

A time-resolved resonance Raman analysis shows that the vinyl stretching band (1629 cm−1) of the O2-binding heme of cytochrome c oxidase shifts to 1627 cm−1 instantaneously upon photolysis of CO and remains for at least 5 ms before reaching the static band (1626 cm−1). Within the same time scale, an intermediate vinyl bending mode of another heme appears at 435 cm−1. These results suggest that both hemes cooperatively control O2 binding by forming an intermediate conformation for effective proton pumping.