Artificial Quinones Replace the Function of Quinone Electron Acceptor (Q<sub>A</sub>) in the Isolated D1-D2-Cytochrome <italic>b<sub>559</sub></italic> Photosystem II Reaction Center Complex

Abstract

Various benzo- and naphthoquinone derivatives were introduced into the purified photosystem II Dl-D2-cytochrome b559 reaction center complex, which lacks the intrinsic plasto-quinone electron acceptors. Effects of these quinones on the electron transfer reactions in nanoseconds to milliseconds time range were studied at room and cryogenic temperatures. 1) The addition of quinones to the purified photosystem II reaction center complex suppressed the nanosecond charge recombination between oxidized reaction center chlorophyll a (P680+) and reduced pheophytin a (Ph−), and stabilized P680+ up to millisecond time range at 280 K and at 77 K. 2) In the reaction center complex supplemented with dibromothymoquinone (DBMIB), P68O was almost fully oxidized and cytochrome b559 was partially reduced by flash excitation. A semi-quinone-like signal with a peak around 320 nm was also induced but the shift of pheophytin absorption band (C55O) was not observed. 3) Halogenated quinones, especially DBMIB, were better electron acceptors than unsubstituted or methylated quinones. 4) The affinities of quinones to the reaction center complex were weakly dependent on their molecular structure.