Artificial Quinones Replace the Function of Quinone Electron Acceptor (QA) in the Isolated D1-D2-Cytochrome b559 Photosystem II Reaction Center Complex

Various benzo- and naphthoquinone derivatives were introducedinto the purified photosystem II Dl-D2-cytochrome b₅₅₉ reactioncenter complex, which lacks the intrinsic plasto-quinone electronacceptors. Effects of these quinones on the electron transferreactions in nanoseconds to milliseconds time range were studiedat room and cryogenic temperatures. 1) The addition of quinonesto the purified photosystem II reaction center complex suppressedthe nanosecond charge recombination between oxidized reactioncenter chlorophyll a (P680⁺) and reduced pheophytin a (Ph^–),and stabilized P680⁺ up to millisecond time range at 280 K andat 77 K. 2) In the reaction center complex supplemented withdibromothymoquinone (DBMIB), P68O was almost fully oxidizedand cytochrome b₅₅₉ was partially reduced by flash excitation.A semi-quinone-like signal with a peak around 320 nm was alsoinduced but the shift of pheophytin absorption band (C55O) wasnot observed. 3) Halogenated quinones, especially DBMIB, werebetter electron acceptors than unsubstituted or methylated quinones.4) The affinities of quinones to the reaction center complexwere weakly dependent on their molecular structure. (Received July 9, 1991; Accepted August 15, 1991)