Proton-coupled electron transfer drives the proton pump of cytochrome c oxidase

Belevich, Ilya
Verkhovsky, Michael I.
Wikström, Mårten

¹Helsinki Bioenergetics Group, Institute of Biotechnology, University of Helsinki, FIN-00014 University of Helsinki, Helsinki, Finland.

doi:10.1038/nature04619

Received 22 September 2005; accepted 1 February 2006.

Supplementary Information is linked to the online version of the paper at www.nature.com/nature.

Author Information Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests. Correspondence and requests for materials should be addressed to M.W. ([email protected]).

Nature 440(7085):p 829-832, April 6, 2006.

Electron transfer in cell respiration is coupled to proton translocation across mitochondrial and bacterial membranes, which is a primary event of biological energy transduction. The resulting electrochemical proton gradient is used to power energy-requiring reactions, such as ATP synthesis. Cytochromecoxidase is a key component of the respiratory chain, which harnesses dioxygen as a sink for electrons and links O₂reduction to proton pumping. Electrons from cytochromecare transferred sequentially to the O₂reduction site of cytochromecoxidase via two other metal centres, Cu_Aand haema,and this is coupled to vectorial proton transfer across the membrane by a hitherto unknown mechanism. On the basis of the kinetics of proton uptake and release on the two aqueous sides of the membrane, it was recently suggested that proton pumping by cytochromecoxidase is not mechanistically coupled to internal electron transfer. Here we have monitored translocation of electrical charge equivalents as well as electron transfer within cytochromecoxidase in real time. The results show that electron transfer from haemato the O₂reduction site initiates the proton pump mechanism by being kinetically linked to an internal vectorial proton transfer. This reaction drives the proton pump and occurs before relaxation steps in which protons are taken up from the aqueous space on one side of the membrane and released on the other.