Long-distance cofactor interactions in terminal oxidases studied by second-derivative absorption spectroscopy

Area of Science:

• Biochemistry
• Spectroscopy
• Enzymology

Background:

• Cytochrome c oxidase is a key enzyme in cellular respiration.
• Understanding its electronic transitions is vital for elucidating its function.
• The Soret transition is a characteristic absorption band for heme proteins.

Purpose of the Study:

• To resolve the electronic transitions of the two heme groups in cytochrome c oxidase.
• To investigate the structural and mechanistic significance of the ferrocytochrome a Soret transition.
• To explore factors influencing the Soret transition, such as ligation state, pH, and complex formation.

Main Methods:

• Application of second-derivative absorption spectroscopy.
• Utilizing cryogenic absorption spectroscopy.
• Analyzing the Soret transition of ferrocytochrome a.

Main Results:

• Both spectroscopic methods resolved the ferrocytochrome a Soret transition into two distinct features at 443 nm and 450 nm.
• The intensity of the 450 nm feature was found to be dependent on the ligation state of cytochrome a3, solution pH, and cytochrome c complex formation.
• This indicates a dynamic and environmentally sensitive electronic structure of cytochrome a.

Conclusions:

• The study provides new insights into the electronic properties of cytochrome c oxidase's heme groups.
• The observed Soret transition splitting is linked to the enzyme's electron transfer and proton translocation activities.
• Further research can explore the precise structural basis for this phenomenon and its functional implications.