PICOSECOND INFRARED STUDY OF THE PHOTODYNAMICS OF CARBONMONOXY-CYTOCHROME-C OXIDASE

Time-resolved infrared (TRIR) techniques have been employed to study the reactions of carbon monoxide with the cytochrome a3-Cu(B) site of cytochrome c oxidase(CcO). The ligation dynamics immediately following photodissociation have been investigated using picosecond TRIR spectroscopy and linear dichroism. The rate of photoinitiated transfer of CO from cytochrome a3 to Cu(B) was measured directly by monitoring the development of the transient Cu(B)CO absorption. In less than 1 ps, a stationary Cu(B)CO spectrum develops, which together with the CO infrared linear dichroism is constant until the CO dissociates from Cu(B) on a microsecond time scale. These observations indicate that the CO is transferred between metals and reaches its equilibrium conformation in less than 1 ps. This unprecedented ligand transfer rate has profound implications with regard to the structure and dynamics of the cytochrome a3-CU(B) site, the functional architecture of the protein, and coordination dynamics in general.