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Proc Natl Acad Sci U S A. 2007 Mar 6;104(10):4200-5. Epub 2007 Feb 28.

The proton pumping pathway of bovine heart cytochrome c oxidase.

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Department of Biochemistry and Integrative Medical Biology, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan.


X-ray structures of bovine heart cytochrome c oxidase have suggested that the enzyme, which reduces O(2) in a process coupled with a proton pumping process, contains a proton pumping pathway (H-pathway) composed of a hydrogen bond network and a water channel located in tandem across the enzyme. The hydrogen bond network includes the peptide bond between Tyr-440 and Ser-441, which could facilitate unidirectional proton transfer. Replacement of a possible proton-ejecting aspartate (Asp-51) at one end of the H-pathway with asparagine, using a stable bovine gene expression system, abolishes the proton pumping activity without influencing the O(2) reduction function. Blockage of either the water channel by a double mutation (Val386Leu and Met390Trp) or proton transfer through the peptide by a Ser441Pro mutation was found to abolish the proton pumping activity without impairment of the O(2) reduction activity. These results significantly strengthen the proposal that H-pathway is involved in proton pumping.

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