Radiative and non-radiative charge recombination pathways in Photosystem II studied by thermoluminescence and chlorophyll fluorescence in the cyanobacterium Synechocystis 6803
Radiative and non-radiative charge recombination pathways in Photosystem II studied by thermoluminescence and chlorophyll fluorescence in the cyanobacterium Synechocystis 6803
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DOI：
10.1016/j.bbabio.2007.01.022
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发表时间：
2007-03-01
影响因子：
4.3
通讯作者：
Vass, Imre
中科院分区：
文献类型：
--
作者：
Cser, Krisztian;Vass, Imre
利用闪光诱导的叶绿素荧光和热释光光谱研究了光系统II中电荷复合的机理。实验在蓝细菌集胞藻6803的完整细胞中进行，其中主要脱镁叶绿素电子受体Phe、主要电子供体P-680和第一醌电子受体Q（A）的氧化还原性质被改变。在D1 G1 n130 Glu或D1 His 198 Ala突变体中，初级自由基对的自由能向更正值移动，S（2）Q（A）（-）和S（2）Q（B）（-）状态的电荷重组相对于野生型加速，如叶绿素荧光产额的更快衰减以及热释光Q和B带的峰温度下移所示。相反的效果，即从S（2）Q（A）（-）和S（2）Q（B）（-）状态的电荷重组的强稳定性，观察到在D1 Gln 130 Leu或D1 His 198 Lys突变体，移动的初级自由基对的自由能水平更负的值，如所示的延迟衰减的闪光诱导的叶绿素荧光和上移的热释光峰温度。重要的是，这些突变引起了热释光强度的急剧变化，表现为D1 Gln 130 Leu和D1 His 198 Lys突变体分别增加了8倍和22倍，以及D1 Gln 130 Glu和D1 His 198 A1 a突变体分别减少了4倍和2.5倍。在存在电子传递抑制剂溴苯腈的情况下，其相对于在DCMU存在下观察到的降低Q（A）/Q（A）（-）的氧化还原电位，在野生型和所有突变菌株中加速了从S（2）Q（A）（-）状态的电荷重组。我们的数据证实，在PSII的电荷重组的主导途径通过P（680）（+）Phe（-）自由基对。这种间接复合分为辐射和非辐射途径，它们通过P-680* 从（1）[P680+Ph-]的再布居和P（680）（+）Q（A）（-）的直接复合进行。这些电荷重组途径的产率以复杂的方式受到光系统II电子转移组分之间的自由能隙的影响：Δ G（P-680* P（680）（+）Phe（-））的增加降低间接辐射途径的产率（在22-0.2%范围内）。另一方面，Δ G（P（680）（+）Phe-P（680）（+）QA（-））的增加增加了直接途径的产率（在2-50%范围内）并降低了间接非辐射途径的产率（在97-37%范围内）。(c)2007 Elsevier B. V.保留所有权利。
The mechanism of charge recombination was studied in Photosystem II by using flash induced chlorophyll fluorescence and thermoluminescence measurements. The experiments were performed in intact cells of the cyanobacterium Synechocystis 6803 in which the redox properties of the primary pheophytin electron acceptor, Phe, the primary electron donor, P-680, and the first quinone electron acceptor, Q(A), were modified. In the D1G1n130Glu or D1His198Ala mutants, which shift the free energy of the primary radical pair to more positive values, charge recombination from the S(2)Q(A)(-) and S(2)Q(B)(-) states was accelerated relative to the wild type as shown by the faster decay of chlorophyll fluorescence yield, and the downshifted peak temperature of the thermoluminescence Q and B bands. The opposite effect, i.e. strong stabilization of charge recombination from both the S(2)Q(A)(-) and S(2)Q(B)(-) states was observed in the D1Gln130Leu or D1His198Lys mutants, which shift the free energy level of the primary radical pair to more negative values, as shown by the retarded decay of flash induced chlorophyll fluorescence and upshifted thermoluminescence peak temperatures. Importantly, these mutations caused a drastic change in the intensity of thermoluminescence, manifested by 8- and 22-fold increase in the D1Gln130Leu and D1His198Lys mutants, respectively, as well as by a 4- and 2.5-fold decrease in the D1Gln130Glu and D1His198A1a mutants, relative to the wild type, respectively. In the presence of the electron transport inhibitor bromoxynil, which decreases the redox potential of Q(A)/Q(A)(-) relative to that observed in the presence of DCMU, charge recombination from the S(2)Q(A)(-) state was accelerated in the wild type and all mutant strains. Our data confirm that in PSII the dominant pathway of charge recombination goes through the P(680)(+)Phe(-) radical pair. This indirect recombination is branched into radiative and non-radiative pathways, which proceed via repopulation of P-680* from (1)[P680+Ph-] and direct recombination of P(680)(+)Q(A)(-). The yield of these charge recombination pathways is affected by the free energy gaps between the Photosystem II electron transfer components in a complex way: Increase of Delta G(P-680* P(680)(+)Phe(-)) decreases the yeild of the indirect radiative pathway (in the 22-0.2% range). On the other hand, increase of Delta G (P(680)(+)Phe- P(680)(+)QA(-)) increases the yield of the direct pathway (in the 2-50% range) and decreases the yield of the indirect non-radiative pathway (in the 97-37% range). (c) 2007 Elsevier B.V. All rights reserved.