Ligand Dynamics in the Binuclear Site in Cytochrome Oxidase

Abstract

The dioxygen-reduction mechanism in cytochrome oxidase relies on proton control of the electron-transfer events that drive the process. Recent work on proton delivery and efflux channels in the protein that are relevant to substrate reduction and proton pumping is considered, and the current status of this area is summarized. Carbon monoxide photodissociation and the ligand dynamics that occur subsequent to photolysis have been valuable tools in probing possible coupling schemes for linking exergonic electron-transfer chemistry to endergonic proton translocation. Our picosecond-time-resolved Raman results show that the heme a 3-proximal histidine bond remains intact following CO photodissociation but that the local environment around the heme a 3 center in the photoproduct is in a nonequilibrium state. This photoproduct relaxes to its equilibrium configuration on the same time scale as ligand release occurs from CuB, which suggests a coupling between the two events and a potential signaling pathway between the site of O2 binding and reduction and the putative element, CuB, that links the redox chemistry to the proton pump.