Interheme electron tunneling in cytochrome c oxidase

Area of Science:

• Biochemistry
• Bioenergetics
• Enzyme kinetics

Background:

• Cytochrome c oxidase (CcO) is the terminal enzyme in the respiratory chain, essential for cellular respiration.
• CcO facilitates the reduction of dioxygen to water, utilizing a heme and copper active site.
• Electron transfer (eT) in oxidoreduction enzymes typically occurs via quantum tunneling.

Purpose of the Study:

• To investigate the mechanism of heme-heme electron transfer (eT) in Cytochrome c oxidase (CcO).
• To determine if the Moser-Dutton equation can predict eT rates in CcO under specific conditions.
• To explore the role of reorganization energy in CcO's electron transfer processes.

Main Methods:

• Utilizing independent molecular dynamics (MD) simulations.
• Employing quantum-chemical (QC) methods for analysis.
• Reinterpreting the Moser-Dutton equation for CcO's specific heme-heme distances.

Main Results:

• Demonstrated that heme-heme eT in CcO exhibits an exceptionally low reorganization energy.
• Showed that the Moser-Dutton equation can predict interheme eT rates in CcO when modified.
• The modified equation considers the average of eT rates weighted by atomic packing densities.

Conclusions:

• CcO's electron transfer mechanism is distinct due to its low reorganization energy.
• A modified Moser-Dutton equation provides accurate predictions for interheme eT in CcO.
• This reinterpretation is crucial for understanding eT at short donor-acceptor distances.