Energetics of primary and secondary electron transfer in Photosystem II membrane particles of spinach revisited on basis of recombination-fluorescence measurements
Energetics of primary and secondary electron transfer in Photosystem II membrane particles of spinach revisited on basis of recombination-fluorescence measurements
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DOI：
10.1016/j.bbabio.2005.03.007
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发表时间：
2005-06-30
影响因子：
4.3
通讯作者：
Dau, H
中科院分区：
文献类型：
--
作者：
Grabolle, M;Dau, H
植物Photosystein II(PSII)的大约200个叶绿素中的一个对光子的吸收导致形成平衡的激发态(Chl200*)，随后是叶绿素氧化(形成P680+)，结合特定的植酸(Phe)，然后电子从Phe-转移到牢固结合的苯醌(QA)，随后P680+被氧化还原活性酪氨酸残基Z还原。涉及的自由能差(Delta G)和氧化还原电位是最重要的。在5℃下对菠菜PSⅡ膜颗粒的放氧过程进行了研究。通过对延迟和瞬时Chl荧光的分析，我们确定了Ch1200*与[Z+，QA-]自由基对在10 mU S处的平衡常数为-0.43+/-0.025 eV。根据这个值和以前发表的结果，计算出P680*和[P680+，QA-]之间的自由能差为-0.50+/-0.04 eV，与电子从Phe到QA的转移有关的自由能损失为0.34+/-0.04 eV。给定的不确定度范围不代表标准偏差或可能的误差，而是对最大误差的估计。假设QA/QA氧化还原电位为-0.08V[Krieger等人，1995，Biochim.生物群落。，得到了如下氧化还原电位估计值：P680/P680++1.25V；Z/Z+(S 10亩)+1.21V；Phe-/Phe-0.42V；P680*/P680+-0.58V。(C)2005 Elsevier B.V.保留所有权利。
Photon absorption by one of the roughly 200 chlorophylls of the plant Photosystern II (PSII) results in formation of an equilibrated excited state (Chl200*) and is followed by chlorophyll oxidation (formation of P680+) coupled to reduction of a specific pheophytin (Phe), then electron transfer from Phe- to a firmly bound quinone (QA), and subsequently reduction of P680+ by a redox-active tyrosine residue denoted as Z. The involved free-energy differences (Delta G) and redox potentials are of prime interest. Oxygen-evolving PSII membrane particles of spinach were studied at 5 degrees C. By analyzing the delayed and prompt Chl fluorescence, we determined the equilibrium constant and thus free-energy difference between Chl200* and the [Z+,QA-] radical pair to be -0.43 +/- 0.025 eV, at 10 mu s after the photon absorption event for PSII in its S-3-state. On basis of this value and previously published results, the free-energy difference between P680* and [P680+,QA-] is calculated to be -0.50 +/- 0.04 eV, the free-energy loss associated with electron transfer from Phe to QA is found to be 0.34 +/- 0.04 eV. The given uncertainty ranges do not represent a standard deviation or likely error, but an estimate of the maximal error. Assuming a QA-/QA redox potential of -0.08 V [Krieger et al., 1995, Biochim. Biophys. Acta 1229, 193], the following redox-potential estimates are obtained: +1.25 V for P680/P680+; +1.21 V for Z/Z+ (at 10 mu s); -0.42 V for Phe-/Phe; -0.58 V for P680*/P680+. (c) 2005 Elsevier B.V. All rights reserved.