Measurement of the midpoint potential of the pheophytin acceptor of photosystem II

摘要: Primary photochemistry in photosystem II (PSII) involves at least three components: (1) P680, the primary electron donor [ 11, which has been reported to be a chlorophyll dimer [2,3] or trimer [3] although recent evidence favors its identification as monomeric species [4,5]; (2) Q, special plastoquinone [6], functions relatively stable acceptor (200-600 ps room temperature when secondary transport is not blocked [7]); (3) Ph, pheophytin molecule an intermediate carrier between P680 and Q. The involvement of PSI1 was initially demonstrated [8-lo]. Reversible photo-reduction observed Q chemically reduced. At same time unsplit EPR radical signal attributed Phwas [lo]. Later it shown that split could photo-induced under some circumstances this reduced Ph involved interaction with semiquinone-iron form 1 l] by analogy situation photosynthetic bacteria 121. Similar [S] optical spectra 200 K 131 were different reaction center preparation. These also anion. Recent ENDOR measurements are consistent anion 141. Also picosecond time-resolved spectrum Phhas particles s]. Strong for presence come from discovery triplet state