The effect of dehydration on the kinetics of forward electron transfer (ET) has been studied in cyanobacterial photosystem I (PS I) complexes in a trehalose glassy matrix by time-resolved optical and EPR spectroscopies in the 100 fs to 1 ms time domain. The kinetics of the flash-induced absorption changes in the subnanosecond time domain due to primary and secondary charge separation steps were monitored by pump-probe laser spectroscopy with 20-fs lowenergy pump pulses centered at 720 nm. The back-reaction kinetics of P700 were measured by high-field time-resolved EPR spectroscopy and the forward kinetics of A1A•-/A1B•-Fx by time-resolved optical spectroscopy at 480 nm. The kinetics of the primary ET reactions to form the primary P•+700 A0•-and the secondary P•+700 A0•-ion radical pairs were not affected by dehydration in the trehalose matrix, while the yield of the P•+700 A1. was decreased by ~20%. Forward ET from the phylloquinone molecules in the A1A•. and A1B. sites to the iron-sulfur cluster FX slowed from ~ 220 ns and ~ 20 ns in solution to ~ 13 μs and ~ 80 ns, respectively. However, as shown by EPR spectroscopy, the ~ 15 μs kinetic phase also contains a small contribution from the recombination between A1B•. and P•+700. These data reveal that the initial ET reactions from P700 to secondary phylloquinone acceptors in the A-and B-branches of cofactors (A1A and A1B) remain unaffected whereas ET beyond A1A and A1B is slowed or prevented by constrained protein dynamics due to the dry trehalose glass matrix.
|Original language||English (US)|
|Number of pages||21|
|Journal||Zeitschrift fur Physikalische Chemie|
|State||Published - Feb 1 2017|
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry