Kinetic and Energetic Model for the Primary Processes in Photosystem II.
Biophysical Journal
|May 12, 2009
Summary
Photosystem II (PS II) reaction centers control charge separation efficiency. Closing the reaction center (RC) significantly reduces charge separation, leading to prompt fluorescence and decreased radical pair formation.
Area of Science:
- Photosynthesis research
- Biophysical chemistry
- Molecular biology
Background:
- Photosystem II (PS II) is crucial for oxygenic photosynthesis.
- Understanding exciton dynamics and charge separation is key to PS II function.
- Previous studies utilized picosecond data for PS II analysis.
Purpose of the Study:
- To develop a detailed kinetic and energetic model for PS II processes.
- To calculate rate constants for exciton trapping, charge separation, recombination, and stabilization.
- To analyze these processes in both open and closed reaction centers (RC).
Main Methods:
- Utilized picosecond spectroscopic data from oxygen-evolving PS II particles.
- Calculated rate constants for open and closed reaction centers.
- Modeled exciton trapping, charge separation, recombination, and stabilization.
Main Results:
- Charge separation in PS II is limited by shallow traps and the P(680) chlorophyll donor.
- Rate of charge separation decreases ~6-fold in closed RCs (Q-reduced) vs. open RCs (Q-oxidized).
- Charge separation is exergonic (~38 meV) in open RCs and endergonic (~12 meV) in closed RCs.
Conclusions:
- The redox state of Quinone (Q) critically controls radical pair formation yield and exciton lifetime.
- Long-lived fluorescence in closed PS II RCs is identified as prompt fluorescence.
- Primary radical pair formation is significantly diminished when PS II reaction centers are closed.
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