Electron spin echo studies of cytochrome c oxidase

Area of Science:

• Biophysics
• Biochemistry
• Electron Paramagnetic Resonance (EPR) Spectroscopy

Background:

• Beef heart cytochrome c oxidase contains EPR-detectable copper, crucial for its enzymatic function.
• Previous models proposed a tetrahedral copper site to explain its unusual EPR spectrum.

Purpose of the Study:

• To investigate the linear electric field effect on the EPR signal of copper in beef heart cytochrome c oxidase.
• To compare these findings with various copper(II) model compounds and other copper proteins.

Main Methods:

• Pulsed Electron Paramagnetic Resonance (EPR) spectroscopy.
• Application of a linear electric field effect analysis.
• Comparative study with square planar and tetrahedral Cu(II) complexes, and Type 1 and Type 2 copper proteins.

Main Results:

• Electric field induced g shifts in cytochrome oxidase are comparable to simple Cu(II) complexes and Type 2 copper sites.
• Observed shifts are smaller than those in tetrahedral copper complexes and Type 1 copper sites.
• The magnetic field dependence of the linear electric field effect in cytochrome oxidase differs significantly from all studied Cu(II) complexes and Type 1 copper.

Conclusions:

• The observed linear electric field effect in beef heart cytochrome c oxidase does not support the proposed tetrahedral Cu(II) model.
• Findings suggest a different coordination environment or electronic structure for the EPR-detectable copper in cytochrome c oxidase.