Electronic pathway in reaction centers from Rhodobacter sphaeroides and Chloroflexus aurantiacus

Area of Science:

• Biochemistry
• Photosynthesis research
• Molecular biophysics

Background:

• Bacterial reaction centers (RCs) are crucial for photosynthesis.
• Understanding electron transfer (ET) kinetics is key to elucidating energy conversion mechanisms.
• Previous models often simplified the complex electronic and energetic factors within RCs.

Purpose of the Study:

• To investigate the electron transfer (ET) kinetics in Chloroflexus aurantiacus and Rhodobacter sphaeroides reaction centers (RCs).
• To explore the role of electronic coupling and free energy asymmetry in directing charge separation.
• To compare the applicability of coherent and incoherent ET models at low temperatures.

Main Methods:

• Utilized incoherent electron transfer models for C. aurantiacus RCs.
• Applied both coherent and incoherent electron transfer models for R. sphaeroides H(M182)L mutant RCs.
• Performed theoretical predictions for electron transfer at very low temperatures.

Main Results:

• Asymmetry in electronic coupling parameters is essential for explaining experimental data in C. aurantiacus RCs.
• Asymmetry in free energy levels of L- and M-side cofactors likely causes ET asymmetry in R. sphaeroides RCs.
• Both coherent and incoherent models provide insights into the observed ET kinetics in R. sphaeroides.

Conclusions:

• Unidirectional charge separation in C. aurantiacus RCs is primarily driven by differences in electronic coupling.
• ET asymmetry in R. sphaeroides RCs is mainly attributed to asymmetric free energy levels.
• The study highlights the importance of considering specific asymmetries for accurate ET modeling in RCs.