Time-resolved optical absorption studies of cytochrome oxidase dynamics

Area of Science:

• Biochemistry
• Biophysics
• Enzyme kinetics

Background:

• Cytochrome c oxidase (CcO) is crucial for cellular respiration, catalyzing the reduction of oxygen to water.
• Understanding CcO's complex reaction mechanism is vital for cellular energy production.

Purpose of the Study:

• To elucidate the time-resolved dynamics of bovine heart cytochrome c oxidase.
• To investigate intramolecular electron transfer and dioxygen reduction pathways.
• To explore the role of the histidine-tyrosine cofactor.

Main Methods:

• Time-resolved spectroscopy (optical absorption, EPR, FTIR).
• Photolysis of carbon monoxide (CO) from mixed-valence enzyme.
• Pulse radiolysis and light-induced electron injection.
• CO flow-flash method and caged dioxygen carriers.
• Synthesis and characterization of a cross-linked histidine-phenol.

Main Results:

• A pH-dependent, branched mechanism for dioxygen reduction, deviating from the conventional sequential model.
• Evidence for P and F forms with pH-dependent interconversion rates.
• Characterization of a radical species on the phenoxyl ring of a synthesized His-Tyr cofactor after UV photolysis.

Conclusions:

• The dioxygen reduction mechanism in CcO is more complex than previously thought, involving branched pathways.
• The histidine-tyrosine cofactor plays a significant role, potentially involving radical intermediates.
• These findings provide new insights into the functional dynamics of cytochrome c oxidase.