Ultrafast photochemistry of the bc₁ complex

Area of Science:

• Biochemistry
• Biophysics
• Spectroscopy

Background:

• The cytochrome bc1 complex is a crucial energy-transducing enzyme.
• It contains multiple redox-active centers, including hemes and an iron-sulfur cluster.
• Understanding its ultrafast dynamics is key to elucidating its function.

Purpose of the Study:

• To investigate ultrafast light-induced events in the cytochrome bc1 complex.
• To characterize the photoresponse of its redox-active components.
• To clarify the behavior of b-hemes upon photoexcitation.

Main Methods:

• Transient absorption spectroscopy was employed.
• Excitation targeted different redox centers under varied conditions.
• Probing spanned the visible spectrum across multiple redox states.

Main Results:

• All ferrous hemes exhibited photodissociation of axial ligands, with rebinding in 5-7 ps.
• Ligand binding kinetics indicate a rigid heme environment.
• Photoactivity of the iron-sulfur center was observed for the first time.

Conclusions:

• The findings support a rigid environment for the hemes, consistent with electron transfer.
• The study refutes photooxidation of b-hemes, contrasting with prior assessments.
• The photoactivity of iron-sulfur clusters offers new possibilities for studying photochemistry in protein complexes.