Role of Protons in Photosynthetic Water Oxidation: pH Influence on the Rate Constants of the S-state Transitions and Hypotheses on the S2→S3 Transition
The mode of proton relocation from the wateroxidizing Mn complex of Photosystem Ⅱ (PSⅡ) toward the aqueous phase is of key importance in photosynthetic water oxidation. An adequate description of the interrelation of proton and electron removal from the Mn complex is still lacking. We reinvestigate the influence of the pH on the rate constants of the redox transitions of the Mn complex (S-state transitions). For high-activity PSⅡ membrane particles from spinach, near-UV absorption transients (at 360 nm) induced by trains of ns-Laser flashes were analyzed. To obtain the rate constants of the pure S-state transitions, a stringent deconvolution of the raw transients was carried out. The transients of the S1→S2 and S2→S3 transitions exhibit mono-exponential behavior whereas the transients of the S3→S0 + O2 transition display a lag-phase behavior that is assignable to formation of a reaction intermediate by deprotonation. The rate constants of the electron transfer (ET) in the S1→S2 and S3→S0 transitions exhibit a negligible pHdependence only. The rate constant of the S2→S3 transition decreases below pH 6 significantly, but clearly less than those of the lag-phase in the S3 →S0 transition. Two models for the coupling of electron and proton transfer in the S2→S3 transition are discussed.
Electron transfer Oxygen evolution Photosystem Ⅱ Proton transfer
L(a)szló Gerencsér Holger Dau
Fachbereich Physik, Freie Universit(a)t Berlin, Arnimallee 14., Berlin, Germany
国际会议
15th International Conference on Photosynthesis(第15届国际光合作用大会)
北京
英文
244-249
2010-08-22（万方平台首次上网日期，不代表论文的发表时间）