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Electron transfer rates and equilibrium within cytochrome c oxidase
O Farver1, O Einarsdóttir, I Pecht
1Institute of Analytical Chemistry, The Royal Danish School of Pharmacy, Copenhagen, Denmark. of@dfh.dk
European Journal of Biochemistry
|February 15, 2000
Summary
Investigating electron transfer (ET) in bovine cytochrome c oxidase reveals rapid equilibration between the CuA center and heme a. This intramolecular ET process is crucial for understanding enzyme function and energy conversion.
Area of Science:
- Biochemistry
- Bioenergetics
- Electron Transfer
Background:
- Cytochrome c oxidase is a key enzyme in cellular respiration.
- Understanding electron transfer pathways is vital for elucidating enzyme mechanisms.
Purpose of the Study:
- To investigate intramolecular electron transfer (ET) between the CuA center and heme a in bovine cytochrome c oxidase.
- To determine the kinetics and thermodynamics of this ET process.
Main Methods:
- Pulse radiolysis was employed to initiate and monitor electron transfer.
- Absorption spectroscopy at 830 nm, 445 nm, and 605 nm was used to track redox changes.
Main Results:
- CuA was rapidly reduced by 1-methyl nicotinamide radicals, followed by partial reoxidation.
- Heme a reduction occurred concomitantly with CuA reoxidation, indicating fast equilibration.
- Rate constants for CuA to heme a ET (13,000 s⁻¹) and reverse (3,700 s⁻¹) were determined, yielding an equilibrium constant of 3.4.
Conclusions:
- A rapid intramolecular electron equilibration exists between CuA and heme a in bovine cytochrome c oxidase.
- The determined ET rate constants and low activation barriers provide insights into ET pathways and reorganization energies.
- These findings contribute to understanding the structural and energetic factors governing electron transfer in metalloenzymes.