Reaction of Reconstituted Acceptor Quinone and Dynamic Equilobration of Electron Transfer in the Photosystem I Reaction Center : MEMBRANES AND BIOENERGETICS

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Electron transfer mechanism in the spinach photosystem I reaction center that contains artificial quinones in place of phylloquinone (2-methyl-3-phytyl-1,4-naphthoquinone, vitamin K_1) as the secondary electron acceptor, Q_Φ (or A_1) was discussed. (1) Most of the reconstituted quinones oxidized the primary acceptor chlorophyll a, A_0, at a rate rapid enough to compete against the charge recombination between A_1^- and the oxidized donor chlorophyll P700^+. (2) The pathway of electron transfer from the semiquinone^⨪ varied depending on the redox potential value of each semiquinone^⨪/quinone couple. Low potential quinones reduced the tertiary acceptor iron-sulfur center, Fx, while the high potential ones reduced P700^+ directly with a 200-μs half-time. (3) The E_m value of each semiquinone*/quinone couple in situ in the reaction center was estimated to be shifted by about 0.3 volt to the negative side from their half wave redox potential values that were measured polarographically in dimethylformamide. The shift seems to represent the acceptor property of the protein environment at the Q_Φ site. (4) The E_m of reconstituted phylloquinone was estimated to be 50-80 mV more negative than that of F_X(5) The mechanism of efficient electron transfer in the reaction center was discussed based on the dynamic equilibria between the electron transfer components and on the estimated E_m values.
日本植物生理学会の論文