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首页> 外文期刊>Biochimica et biophysica acta. Bioenergetics >A two-electron reaction at the catalytic site of water oxidation in manganese-depleted Photosystem II vesicles in the presence of an electron donor. Coupled electron and proton transfer processes
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A two-electron reaction at the catalytic site of water oxidation in manganese-depleted Photosystem II vesicles in the presence of an electron donor. Coupled electron and proton transfer processes

机译：在电子供体存在的情况下，贫锰的光系统II囊泡中水氧化催化部位的两电子反应。电子和质子传递过程耦合

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摘要

We have studied the electron and proton transfer at the manganese-depleted catalytic site of water oxidation in the presence of the electron donor 1,5-diphenylcarbazide (DPC). On the basis of measurements of flash-induced fluorescence yield, electrochromic bandshifts and pH transients into the aqueous medium, we have been led to the following conclusions: (1) The electron donor DPC was involved in a two sequential photostep process just like Mn2+ in photoactivation. After a first flash, the product of the reaction of DPC with the first Photosystem II charge separation was unstable (half-decay around 1 s at pH 6.5) until converted into a stable one by a second flash. The formation of the unstable intermediate was rather favored at alkaline pH. Its concentration increased progressively with pH to reach a maximum at pH 7.2–7.4. Nevertheless, consumption of this intermediate required a proton binding, since its regeneration after the second flash needed a latency dark time inversely proportional to proton concentration. (2) Each step of the process was accompanied by proton exchange with the medium. At acidic pH, the odd flashes in a series induced acidification, whereas on even flashes occurred alkalinization. The pattern of proton release/uptake varied extremely as a function of pH, between 4 H+ and -2 H+/e-, with opposite changes at acidic and basic pH. At neutral pH, 1 H+/e- was assumed to be released at each step. On the basis of these results and data already in the literature, the molecular details of the pH-dependent part of the deprotonation are discussed in terms of electrostatic interactions between the polarized catalytic center and bound H+ and OH? ions. The described two-photostep process is proposed to reflect the two-electron water oxidation to an hydrogen peroxide intermediate.
机译：我们已经研究了在电子给体1,5-二苯卡巴肼（DPC）存在的情况下，缺锰的水氧化催化位上的电子和质子转移。根据闪光诱导的荧光产量，电致变色带移和进入水介质的pH瞬变的测量，我们得出以下结论：（1）电子给体DPC参与了两个连续的光步过程，就像Mn2 +光活化。第一次闪蒸后，DPC与第一次Photosystem II电荷分离的反应产物不稳定（在pH 6.5时约1 s衰减一半），直到第二次闪蒸转变为稳定的为止。在碱性pH下，不稳定中间体的形成是非常有利的。其浓度随pH逐渐增加，在pH 7.2–7.4达到最大值。然而，消耗该中间体需要质子结合，因为其在第二次闪蒸后的再生需要与质子浓度成反比的潜伏时间。 （2）过程的每个步骤都伴随着与介质的质子交换。在酸性pH值下，奇数次闪烁会引起一系列酸化，而在偶数次闪烁会发生碱化。质子释放/吸收的模式随pH的变化而变化很大，介于4 H +和-2 H + / e-之间，而在酸性和碱性pH下则相反。在中性pH下，假定每个步骤释放1 H + / e-。基于这些结果和文献中已有的数据，根据极化催化中心与结合的H +和OH？之间的静电相互作用，讨论了去质子的pH依赖部分的分子细节。离子。提出了所描述的两步法工艺，以将双电子水氧化反应为过氧化氢中间体。

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