Time-resolved infrared studies of the dynamics of ligand binding to cytochrome c oxidase.

摘要

Time-resolved infrared spectroscopy (TRIRS) has been employed to study the reactions of small molecules with the cytochrome a(sub 3)-Cu(sub B) site of cytochrome c oxidase (CcO). All phases of these reactions have been investigated, from ultrafast phenomena (hundreds of femtoseconds) to relatively slow processes (milliseconds). The ligation dynamics immediately following photodissociation have been studied using a TRIR technique with time resolution of less than 1 ps. The rate of photoinitiated transfer of CO from Fe(sub a3)(sup 2+) to Cu(sub B)(sup +) was measured directly by monitoring the development of the transient Cu(sub B)(sup +)-CO absorption. The development of a stationary Cu(sub B)(sup +)-CO spectrum which is constant until the CO dissociates from Cu(sub B)(sup +) occurs in less than 1 ps, indicating that the photoinitiated transfer of CO is remarkably fast. This unprecedented ligand transfer rate has profound implications with regard to the structure and dynamics of the cytochrome a(sub 3)-Cu(sub B) site, the functional architecture of the protein and coordination dynamics in general. The photodissociation and recombination of Cn(sup (minus)) has also been studied using a real-time TRIR technique. The CN(sup (minus)) recombination rate of 430 s(sup (minus)1) is consistent with a recombination pathway similar to the one they have previously proposed for CO. The authors suggest the rate determining step for CN(sup (minus)) recombination is the thermal dissociation of the Fe(sub a3)(sup 2+)-L bond. 25 refs., 7 figs.