Proton/hydrogen transfer affects the S-state-dependent microsecond phases of P680+ reduction during water splitting

被引:106
作者
Schilstra, MJ
Rappaport, F
Nugent, JHA
Barnett, CJ
Klug, DR [1 ]
机构
[1] Univ London Imperial Coll Sci Technol & Med, Mol Dynam Grp, London SW7 2AY, England
[2] Univ London Imperial Coll Sci Technol & Med, Dept Biochem & Chem, Ctr Photomol Sci, Photosynth Res Grp, London SW7 2AY, England
[3] Inst Biol Physicochim, F-75005 Paris, France
[4] Univ London Univ Coll, Dept Biol, London WC1E 6BT, England
关键词
D O I
10.1021/bi9713815
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
To investigate a possible coupling between P680(+) reduction and hydrogen transfer, we studied the effects of H2O/D2O exchange on the P680(+) reduction kinetics in the nano-and microsecond domains. We concentrated on studying the period-4 oscillatory (i.e., S-state-related) part of the reduction kinetics, by analyzing the differences between the P680(+) reduction curves, rather than the full kinetics. Earlier observations that P680(+) reduction kinetics have microsecond components were confirmed: the longest observable lifetime whose amplitude showed period-4, oscillations was 30 mu s. We found that solvent isotope exchange left the nanosecond phases of the P680(+) reduction unaltered. However, a significant effect on the oscillatory microsecond components was observed. We propose that, al least in the S-0/S-1 and S-3/S-0 transitions, hydrogen (proton) transfer provides an additional decrease in the free energy of the Y(Z)(+)P680 state with respect to the Y(Z)P680(+) state. This implies that relaxation of the state Y(Z)(+)P680 is required for complete reduction of P680(+) and for efficient water splitting. The kinetics of the P680(+) reduction suggest that it is intraprotein proton/hydrogen rearrangement/transfer, rather than proton release to the bulk, which is occurring on the 1-30 mu s time scale.
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页码:3974 / 3981
页数:8
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