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Pathways for electron tunneling in cytochrome c oxidase
J J Regan1, B E Ramirez, J R Winkler
1Beckman Institute, California Institute of Technology, Pasadena 91125, USA.
Journal of Bioenergetics and Biomembranes
|June 12, 1998
Summary
Electron transfer in cytochrome c oxidase involves specific pathways between redox sites like CuA, heme a, and heme a3. These pathways, influenced by redox states, are crucial for gating electron flow in proton pumps.
Area of Science:
- Biochemistry
- Biophysics
- Molecular Biology
Background:
- Cytochrome c oxidase (COX) is a crucial enzyme in cellular respiration.
- Historical discoveries trace the identification of its redox centers, including heme a, heme a3, CuB, and CuA.
- Understanding the electron transfer pathways within COX is key to its function.
Purpose of the Study:
- To elucidate the electron tunneling pathways and rates within cytochrome c oxidase.
- To investigate the role of specific amino acid residues and redox interactions in electron transfer.
- To model the gating mechanism of electron flow in proton pumps.
Main Methods:
- Computational analysis of electron tunneling pathways.
- Comparison of calculated rates with experimental data, incorporating corrections for driving force and reorganization energy.
- Examination of historical research and structural data on COX redox sites.
Main Results:
- Calculated electron transfer rates for CuA to heme a (9 x 10^5 s^-1) and heme a to heme a3 (7 x 10^6 s^-1) agree with experimental findings.
- The optimal CuA-heme a pathway involves His204, not Cys196.
- Efficient heme a-heme a3 transfer utilizes His378, His376, and Phe377; direct CuA-heme a3 transfer is significantly slower.
Conclusions:
- Electron transfer in COX is highly specific, with defined pathways and rates.
- Redox interactions and specific amino acid residues play critical roles in modulating electron flow.
- The identified pathways provide a model for understanding electron gating in proton-pumping mechanisms.