Proton uptake and release in cytochrome c oxidase: separate pathways in time and space?

Analysis of mutant forms of cytochrome c oxidase in conjunction with knowledge from high resolution crystal structures is providing important clues as to the location and specificity of proton channels and the timing of proton movements with respect to electron transfer events. Mutant forms of Rhodobacter sphaeroides cytochrome c oxidase at the highly conserved aspartate 132, in the 'D-channel' and at lysine 362, in the 'K-channel', are compared with respect to the nature of their residual activity and their reactions with H2O2. The results argue for physical separation and specificity in these two proton input routes, due to their distinctive kinetics with peroxide and the apparent connection of the D-channel, but not the K-channel, to the proton exit pathway. The reversible nature and possible location of the exit pathway are discussed in the context of direct and indirect mechanisms of energy coupling.