Redox transitions between oxygen intermediates in cytochrome-c oxidase

Area of Science:

• Biochemistry
• Enzymology
• Spectroscopy

Background:

• Cytochrome-c oxidase catalyzes the reduction of oxygen to water, a crucial process in cellular respiration.
• The enzyme involves several intermediates, including the peroxy (P) and ferryl (F) forms, whose structures and redox states have been debated.
• Understanding these intermediates is key to elucidating the complete oxygen reduction mechanism.

Purpose of the Study:

• To clarify the redox states and structural properties of the peroxy (P) and ferryl (F) intermediates of cytochrome-c oxidase.
• To resolve recent controversies regarding the structures and overall redox states of these oxygen reaction intermediates.

Main Methods:

• Utilized optical, Raman, and magnetic circular dichroism spectroscopy for characterization.
• Employed tris(2,2'-bipyridyl)ruthenium(II) as a photoinducible reductant for controlled one-electron reduction steps.
• Generated P and F forms via reactions of the oxidized enzyme with H2O2 or the two-electron reduced enzyme with O2.

Main Results:

• Demonstrated that one-electron reduction of the peroxy (P) form yields the ferryl (F) form.
• Showed that one-electron reduction of the ferryl (F) form regenerates the oxidized enzyme.
• Confirmed that P and F states represent two- and one-electron reduction equivalents relative to the oxidized enzyme, respectively.

Conclusions:

• The study provides definitive evidence for the redox relationships between the P, F, and oxidized forms of cytochrome-c oxidase.
• The findings help to resolve ambiguities concerning the redox states of key intermediates in the oxygen reduction pathway.
• Further discussion on the structures of the P and F states is presented based on the established redox states.