Open AccessRedox-coupled proton translocation in biological systems: Proton shuttling in cytochrome c oxidase
Author(s) -
Andreas Namslauer,
Ashtamurthy S. Pawate,
Robert B. Gennis,
Peter Brzezinski
Publication year - 2003
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.2432106100
Subject(s) - rhodobacter sphaeroides , chemistry , cytochrome c oxidase , proton pump , ubiquinol , proton , electrochemical gradient , chemiosmosis , proton transport , electron transport complex iv , oxidase test , cytochrome , biophysics , atp synthase , mutant , redox , catalysis , photochemistry , biochemistry , cytochrome c , enzyme , membrane , coenzyme q – cytochrome c reductase , atpase , mitochondrion , biology , photosynthesis , inorganic chemistry , physics , quantum mechanics , gene
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 (CcO) 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 CcO from Rhodobacter sphaeroides [Asn-139 --> Asp, ND(I-139)] in which proton pumping is completely uncoupled from the catalytic turnover (i.e., reduction of O2). However, in this mutant CcO, the rate by which O2 is reduced to H2O is even slightly higher than that of the wild-type CcO. The data indicate that the disabling of the proton pump is a result of a perturbation of E(I-286), which is located 20 A from N(I-139) and is an internal proton donor to the catalytic site, located in the membrane-spanning part of CcO. The mutation results in raising the effective pKa 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 CcO pumps protons.