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Redox-coupled proton translocation in biological systems: Proton shuttling in cytochrome c oxidase

2003; National Academy of Sciences; Volume: 100; Issue: 26 Linguagem: Inglês

10.1073/pnas.2432106100

1091-6490

Andreas Namslauer, Ashtamurthy S. Pawate, Robert B. Gennis, Peter Brzezinski,

Spectroscopy and Quantum Chemical Studies

In the respiratory chain free energy is conserved by linking the chemical reduction of dioxygen to the electrogenic translocation of protons across a membrane. Cytochrome c oxidase (C c O) is one of the sites where this linkage occurs. Although intensively studied, the molecular mechanism of proton pumping by this enzyme remains unknown. Here, we present data from an investigation of a mutant C c O from Rhodobacter sphaeroides [Asn-139 → Asp, ND(I-139)] in which proton pumping is completely uncoupled from the catalytic turnover (i.e., reduction of O 2 ). However, in this mutant C c O, the rate by which O 2 is reduced to H 2 O is even slightly higher than that of the wild-type C c O. The data indicate that the disabling of the proton pump is a result of a perturbation of E(I-286), which is located 20 Å from N(I-139) and is an internal proton donor to the catalytic site, located in the membrane-spanning part of C c O. The mutation results in raising the effective pK a of E(I-286) by 1.6 pH units. An explanation of how the mutation uncouples catalytic turnover from proton pumping is offered, which suggests a mechanism by which C c O pumps protons.