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Dynamics of Electron Transfer Pathways in Cytochrome c Oxidase

Center for Theoretical Biological Physics and Department of Physics, University of California at San Diego, La Jolla, California 92093–0374

Correspondence: Address reprint requests to José Nelson Onuchic, E-mail: jonuchic{at}ucsd.edu.

Cytochrome c oxidase mediates the final step of electron transfer reactions in the respiratory chain, catalyzing the transfer between cytochrome c and the molecular oxygen and concomitantly pumping protons across the inner mitochondrial membrane. We investigate the electron transfer reactions in cytochrome c oxidase, particularly the control of the effective electronic coupling by the nuclear thermal motion. The effective coupling is calculated using the Green's function technique with an extended Huckel level electronic Hamiltonian, combined with all-atom molecular dynamics of the protein in a native (membrane and solvent) environment. The effective coupling between Cu_A and heme a is found to be dominated by the pathway that starts from His^B204. The coupling between heme a and heme a₃ is dominated by a through-space jump between the two heme rings rather than by covalent pathways. In the both steps, the effective electronic coupling is robust to the thermal nuclear vibrations, thereby providing fast and efficient electron transfer.

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