Electron paramagnetic resonance kinetic studies of the S states in spinach thylakoids.

摘要: The Tyrz+ decay kinetics have been analyzed by using time-resolved EPR to determine the half-time of each Si-->S(i + 1) transition in O2-evolving complex spinach thylakoids under physiological conditions. Using dark-adapted and appropriate single-turnover flash sequences, we were able detect signal IIvf S0-->Tyrz S1, S1-->Tyrz S2, S2-->Tyrz S3, S3-->(S4)-->Tyrz S0 transitions. To correct for damping S state synchronization during sequence, Kok parameters estimated measuring oxygen pattern situ nitroxide-based oximetry. Following deconvolution individual contributions, yield following half-times transitions: S0-->S1 40-60 microseconds, S1-->S2 85 S2-->S3 140 S3-->(S4)-->S0 750 microseconds. Preliminary results with detergent-solubilized PSII membranes suggest that S3-->S0 at least is slowed a factor approximately 2 this system. Ramifications these terms electron transfer events on donor site are discussed.