Electrostatic control of charge separation in bacterial photosynthesis.
Electrostatic control of charge separation in bacterial photosynthesis.
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细菌光合作用中电荷分离的静电控制。
DOI：
10.1016/0005-2728(90)90192-7
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发表时间：
1990
期刊：
影响因子：
--
通讯作者：
Warshel,A
中科院分区：
文献类型：
--
作者：
Parson,WW;Chu,ZT;Warshel,A
计算了光合作用细菌反应中心中电子载体与周围环境的静电相互作用能。这些计算是基于绿色红假单胞菌反应中心的详细晶体结构，并使用迭代的自洽程序来评估诱导偶极在蛋白质和周围膜中的影响。为了得到自由基对态的自由能，计算的静电相互作用能与实验测量的电子载流子、细菌叶绿素(BCHL)和细菌叶绿素(BPH)的中点氧化还原电位相结合。P+H−L自由基对，其中一个电子已从初级电子给体(P)移动到反应中心(HL)的‘L’侧的BPH，其位置约为.当自由基对在静态晶体结构中形成时，低于最低激发单线态(P∗)的2.0千卡/摩尔。计算出P+H−L随后松弛的重组能为5.0千卡/摩尔，因此松弛自由基对在P-∗以下约7千卡/摩尔。未弛豫的P+B−L自由基对的电子受体是位于P和HL之间的副BCHL，它与P∗的能量基本相同。P+B−M，其中一个电子在‘M’侧移动到BCHL，计算出它位于P∗上方约5.5千卡/摩尔。这些结果的估计误差范围为±2.5千卡/摩尔。它们对模型的各种细节相对不敏感，包括P+中的电荷分布，氨基酸残基的原子电荷，微观上考虑的结构区域的边界，以及P的组氨酸配体和潜在可电离氨基酸的处理。计算的自由能与电子从P-∗通过BL快速转移到HL是一致的，而对M侧颜料的电子转移则慢得多。酪氨酸M208似乎在降低P+B−L的能量方面起着特别重要的作用。与蛋白质的静电相互作用有利于P+在PM上的正电荷定位，PM是构成电子供体的两个BCHL分子之一。
Electrostatic interaction energies of the electron carriers with their surroundings in a photosynthetic bacterial reaction center are calculated. The calculations are based on the detailed crystal structure of reaction centers fromRhodopseudomonas viridis, and use an iterative, self-consistent procedure to evaluate the effects of induced dipoles in the protein and the surrounding membrane. To obtain the free energies of radical-pair states, the calculated electrostatic interaction energies are combined with the experimentally measured midpoint redox potentials of the electron carriers and of bacteriochlorophyll (BChl) and bacteriopheophytin (BPh) in vitro. The P+H−Lradical-pair, in which an electron has moved from the primary electron donor (P) to a BPh on the ‘L’ side of the reaction center (HL), is found to lie approx. 2.0 kcal / mol below the lowest excited singlet state (P∗), when the radical-pair is formed in the static crystallographic structure. The reorganization energy for the subsequent relaxation of P+H−Lis calculated to be 5.0 kcal / mol, so that the relaxed radical-pair lies about 7 kcal / mol below P∗. The unrelaxed P+B−Lradical-pair, in which the electron acceptor is the accessory BChl located between P and HL, appears to be essentially isoenergetic with P∗. P+B−M, in which an electron moves to the BChl on the ‘M’ side, is calculated to lie about 5.5 kcal / mol above P∗. These results have an estimated error range of ± 2.5 kcal / mol. They are shown to be relatively insensitive to various details of the model, including the charge distribution in P+, the atomic charges used for the amino acid residues, the boundaries of the structural region that is considered microscopically and the treatments of the histidyl ligands of P and of potentially ionizable amino acids. The calculated free energies are consistent with rapid electron transfer from P∗ to HLby way of BL, and with a much slower electron transfer to the pigments on the M side. Tyrosine M208 appears to play a particularly important role in lowering the energy of P+B−L. Electrostatic interactions with the protein favor localization of the positive charge of P+on PM, one of the two BChl molecules that make up the electron donor.