On the role of the K-proton transfer pathway in cytochrome c oxidase
| Autor: | Pia Ädelroth, Magnus Brändén, Andreas Namslauer, Robert B. Gennis, Peter Brzezinski, Håkan Sigurdson |
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| Rok vydání: | 2001 |
| Předmět: |
Models
Molecular Proton Protein Conformation Static Electricity chemistry.chemical_element Electrons Heme Rhodobacter sphaeroides Photochemistry Oxygen Electron Transport Electron Transport Complex IV Electron transfer Cytochrome c oxidase Exergonic reaction Binding Sites Photolysis Multidisciplinary biology Lysine Spectrum Analysis Biological Transport Hydrogen Bonding Biological Sciences biology.organism_classification Electron transport chain Amino Acid Substitution chemistry Mutation biology.protein Protons |
| Zdroj: | Proceedings of the National Academy of Sciences. 98:5013-5018 |
| ISSN: | 1091-6490 0027-8424 |
| DOI: | 10.1073/pnas.081088398 |
| Popis: | Cytochrome c oxidase is a membrane-bound enzyme that catalyzes the four-electron reduction of oxygen to water. This highly exergonic reaction drives proton pumping across the membrane. One of the key questions associated with the function of cytochrome c oxidase is how the transfer of electrons and protons is coupled and how proton transfer is controlled by the enzyme. In this study we focus on the function of one of the proton transfer pathways of the R. sphaeroides enzyme, the so-called K-proton transfer pathway (containing a highly conserved Lys(I-362) residue), leading from the protein surface to the catalytic site. We have investigated the kinetics of the reaction of the reduced enzyme with oxygen in mutants of the enzyme in which a residue [Ser(I-299)] near the entry point of the pathway was modified with the use of site-directed mutagenesis. The results show that during the initial steps of oxygen reduction, electron transfer to the catalytic site (to form the “peroxy” state, P r ) requires charge compensation through the proton pathway, but no proton uptake from the bulk solution. The charge compensation is proposed to involve a movement of the K(I-362) side chain toward the binuclear center. Thus, in contrast to what has been assumed previously, the results indicate that the K-pathway is used during oxygen reduction and that K(I-362) is charged at pH ≈ 7.5. The movement of the Lys is proposed to regulate proton transfer by “shutting off” the protonic connectivity through the K-pathway after initiation of the O 2 reduction chemistry. This “shutoff” prevents a short-circuit of the proton-pumping machinery of the enzyme during the subsequent reaction steps. |
| Databáze: | OpenAIRE |
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