High-Pressure Modulation of Primary Photosynthetic Reactions

Area of Science:

• Biophysics
• Photosynthesis research
• Molecular mechanisms of energy conversion

Background:

• Photochemical charge separation is crucial for biological solar energy conversion.
• The precise mechanism of primary charge separation, despite high quantum efficiency, is not fully understood.

Purpose of the Study:

• To investigate the mechanism of primary charge separation in a YM210W mutant bacterial reaction center.
• To explore the effects of hydrostatic pressure on charge separation dynamics.

Main Methods:

• Utilized ultrafast fluorescence barospectroscopy.
• Applied hydrostatic pressures up to 10 kbar to the bacterial reaction center mutant.

Main Results:

• The rate of primary charge separation increased monotonically with pressure.
• Electron transfer to the secondary acceptor decreased under pressure.
• A pressure-induced hydrogen bond break at ~2 kbar increased the free energy gap, causing a fluorescence drop.

Conclusions:

• Findings support a model incorporating charge recombination and excited primary pair state restoration over a sequential model.
• Pressure accelerates primary electron transfer mainly by increasing electronic coupling energy.
• Primary electron transfer in the studied mutant is nonadiabatic, in the normal region, and thermally activated across all pressures.