Metal site cooperativity within cytochrome oxidase

Area of Science:

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

Background:

• Bovine heart cytochrome oxidase is a crucial enzyme in cellular respiration.
• Understanding the redox properties and interactions of its components is vital for elucidating electron transfer mechanisms.

Purpose of the Study:

• To investigate the formation and redox properties of low-spin cytochrome a3(III)-ligand complexes in bovine heart cytochrome oxidase.
• To explore the potential cooperativity between cytochrome a and copper B (CuB) during enzyme oxidation.

Main Methods:

• Low-temperature (9-15 K) Electron Paramagnetic Resonance (EPR) spectroscopy.
• Potentiometric titration of isolated bovine heart cytochrome oxidase in the presence of azide or cyanide.

Main Results:

• Two distinct species of low-spin cytochrome a3(III)-azide were identified with different g values and midpoint potentials.
• Two low-spin cytochrome a3(III)-cyanide signals were observed, also dependent on the oxidation state of cytochrome a.
• The titration behavior suggests that oxidation of cytochrome a influences the redox potential of CuB.

Conclusions:

• The formation and disappearance of cytochrome a3(III)-ligand signals are linked to the redox state of cytochrome a.
• Data support a model where oxidation of cytochrome a increases the midpoint potential of CuB by approximately 55 mV.
• This implies cooperativity between cytochrome a and CuB in the electron transfer pathway.