Electron-proton interactions in terminal oxidases
| Autor: | Pia Ädelroth, Peter Brzezinski, Håkan Sigurdson, Martin Karperfors, Margareta Svensson Ek, Anna Aagaard |
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| Jazyk: | angličtina |
| Předmět: |
Models
Molecular Proton Cytochrome Stereochemistry Surface Properties Ubiquinol oxidase Static Electricity Biophysics Electrons Flow-flash Biochemistry Catalysis Proton transfer Electron transfer Proton pumping Histidine biology Chemistry Cytochrome c Substrate (chemistry) Biological Transport Cell Biology Proton pump Oxygen biology.protein Protons Oxidoreductases Cytochrome c oxidase |
| Zdroj: | Biochimica et Biophysica Acta (BBA) - Bioenergetics. (1-2):159-169 |
| ISSN: | 0005-2728 |
| DOI: | 10.1016/S0005-2728(98)00058-9 |
| Popis: | The cytochrome c and ubiquinol oxidases discussed in this article are membrane-bound redox-driven proton pumps which couple an electron current to a proton current across the membrane. This coupling requires a control of the thermodynamics and/or rates of internal electron- and proton-transfer reactions (termed 'gating'). Therefore, to understand the structure-function relation of these proton pumps, individual electron- and proton-transfer reactions must be investigated. We have undertaken such studies by using a combination of site-directed mutagenesis and spectroscopic techniques. The results show that proton uptake/release upon reduction/oxidation of heme a3 takes place on a ms-time scale through the K-pathway (including Thr(I-359) and Lys(I-362)), but not through the D-pathway (including Asp(I-132) and Glu(I-286)). During reaction of the reduced enzyme with O2, both substrate and pumped protons are taken up through the D-pathway (but not through the K-pathway) in a biphasic process with time constants of 100 microseconds and 1 ms. Thus, the original assignment of the role of the D-pathway (used only for pumped protons) must be revised. Dynamic studies of proton uptake to the enzyme surface show that on the proton-input side, the surface carries a proton-collecting antenna made of carboxylate and histidine residues which enable the enzyme to pick up protons with a rate compatible to the enzyme turnover rate. These results are consistent with the three-dimensional cytochrome c oxidase structure which shows that the entry point to the D-pathway (but not to the K-pathway) is surrounded by a network of histidine residues within a negative electrostatic potential. |
| Databáze: | OpenAIRE |
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