Proton transfer in uncoupled variants of cytochrome c oxidase

Cytochrome c oxidase is a membrane‐bound redox‐driven proton pump that harbors two proton‐transfer pathways, D and K, which are used at different stages of the reaction cycle. Here, we address the question if a D pathway with a modified energy landscape for proton transfer could take over the role of the K pathway when the latter is blocked by a mutation. Our data indicate that structural alterations near the entrance of the D pathway modulate energy barriers that influence proton transfer to the proton‐loading site. The data also suggest that during reduction of the catalytic site, its protonation has to occur via the K pathway and that this proton transfer to the catalytic site cannot take place through the D pathway.