Evidence for a hydroxide intermediate in cytochrome c oxidase

Area of Science:

• Biochemistry and enzymology
• Spectroscopy
• Protein dynamics

Background:

• Cytochrome c oxidase is a crucial enzyme in cellular respiration.
• Its catalytic mechanism involves transient intermediates that are difficult to detect.
• Hydroxide intermediates have been theoretically proposed but lacked experimental evidence.

Purpose of the Study:

• To generate and characterize a transient intermediate of cytochrome c oxidase.
• To provide the first direct experimental evidence for a hydroxide intermediate.
• To develop a method for stabilizing this transient species.

Main Methods:

• Enzyme turnover was induced by simultaneous photoreductive reduction and chemical oxidation.
• A laser beam was used to expose the enzyme in the presence of oxygen.
• Resonance Raman spectroscopy with isotopic substitution (oxygen and hydrogen) was employed for characterization.

Main Results:

• A transient intermediate was successfully generated and stabilized.
• Resonance Raman spectroscopy revealed a characteristic spectral line at 477 cm-1.
• Isotopic substitution confirmed this line corresponds to an Fe-OH stretching mode, identifying it as a hydroxide intermediate.

Conclusions:

• The study provides the first direct experimental evidence for a hydroxide intermediate in cytochrome c oxidase.
• A novel method using laser irradiation and chemical oxidation allows for the generation and stabilization of this intermediate.
• This finding advances our understanding of cytochrome c oxidase's catalytic mechanism and opens avenues for further mechanistic studies.