Kinetics and pathways of charge recombination in photosystem II

被引:279
作者
Rappaport, F
Guergova-Kuras, M
Nixon, PJ
Diner, BA
Lavergne, J
机构
[1] CNRS, UPR 1261, Inst Biol Phys Chim, F-75005 Paris, France
[2] Univ London Imperial Coll Sci & Technol, Dept Biochem, London SW7 2AY, England
[3] EI Du Pont Nemours & Co, Expt Stn, CR & D, Wilmington, DE 19880 USA
[4] Univ Mediterranee, CEA Cadarache, DSV DEVM,CNRS CEA, Lab Bioenerget Cellulaire,UMR163,CEA1000, F-13108 St Paul Les Durance, France
关键词
D O I
10.1021/bi025725p
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
The mechanism of charge recombination of the S(2)Q(A)(-) state in photosystem II was investigated by modifying the free energy gap between the quinone acceptor Q(A) and the primary pheophytin acceptor Ph. This was done either by changing the midpoint potential of Ph (using mutants of the cyanobacterium Synechocystis with a modified hydrogen bond to this cofactor), or that Of Q(A) (using different inhibitors of the Q(B) pocket). The results show that the recombination rate is dependent on the free energy gap between Ph and Q(A), which confirms that the indirect recombination pathway involving formation of Ph- has a significant contribution. In the mutant with the largest free energy gap, direct electron transfer from In Q(A)(-) to P+ predominates. The temperature dependence of the recombination rate was investigated, showing a lower activation enthalpy in this mutant compared with the WT. The data allow the determination of the rate of the direct route and of its relative weight in the various strains. The set of currently accepted values for the midpoint potentials of the Q(A)/Q(A)(-), Ph/Ph-, and P+/P* couples is not consistent with the relatively rapid rate of the indirect recombination pathway found here, nor with the 3% yield of delayed fluorescence as previously estimated by de Grooth and van Gorkom (1981, Biochim. Biophys. Acta 635, 445-456). It is argued that a likely explanation is that the midpoint potentials of the two latter couples are more positive than believed due to electrostatic interactions. If such is the case, the estimation of the midpoint potential of the P+/P and S-2/S-1 Couples must also be revised upward, with values of 1260 and 1020 mV, respectively.
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页码:8518 / 8527
页数:10
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