Unidirectionality of charge separation in reaction centers of photosynthetic bacteria
Unidirectionality of charge separation in reaction centers of photosynthetic bacteria
复制标题
光合细菌反应中心电荷分离的单向性
DOI：
10.1016/0005-2728(88)90139-9
复制
发表时间：
1988
期刊：
影响因子：
--
通讯作者：
J. Jortner
中科院分区：
文献类型：
--
作者：
M. Michel;M. Plato;J. Deisenhofer;H. Michel;M. Bixon;J. Jortner
时间分辨光谱结合X射线结构数据的反应中心的Rhodopterioraciridis和Rhodobacter sphaeroides揭示了一个分支比a> 5的主要电子转移速率，有利于两个，几乎对称的色素/蛋白质分支，L和M之一。在本文中，我们探讨了这种单向性的电子转移之间的激发单重态的细菌叶绿素二聚体（1 P）和细菌脱镁叶绿素（H）沿着L蛋白亚基的起源。应用非绝热电子转移理论分析了L支和M支上电子转移速率kL和kM的不对称性。这种不对称性源于核弗兰克-康登因子和电子耦合的累积贡献，这两者都增强了L分支上的电子转移速率。核Frank-Condon因子由P+ H-L和P+ H-M态之间的能量差ΔE LM修正，这是由这些离子对态与蛋白质极性基团的静电相互作用以及不对称库仑和介质极化相互作用引起的。计算结果为ΔE LM=−（0.09±0.04）eV，在300 K时产生的核增强贡献为1.5（+ 0.8，− 0.3）to k L k M，因此不足以单独解释观察到的反应中心的不对称性。绿色的对单向性的另一个贡献来源于通过辅助细菌叶绿素（B）的虚拟状态的1 P-BH的电子超交换耦合。利用紧束缚近似和SCF-MO波函数，结合Rps反应中心的辅基和极性氨基酸侧链的结构数据，计算了分子间1 P-B-B L和1 P-B-B M电子相互作用项的比值。绿色的电子超交换对k L k M的增强的贡献约为。8±4。这种不对称性被追溯到M-二聚体组分PM上的过量负电荷密度与结构不对称性的组合，这增强了PM-BL电子重叠。因此，1 P α-B L-H L超交换作用优于1 P α-B M-H M相互作用。不对称核Franck-Condon因子和电子耦合的综合作用产生了Rps反应中心中两个色素分支的电子转移速率的分支比沿着。绿色的一个近似。12（− 7，+ 15）。这足以解释实验观察到的单向性。
Time-resolved spectroscopy in conjunction with X-ray structural data for reaction centers of Rhodopseudomonas viridis and Rhodobacter sphaeroides reveal a branching ratio a> 5 for the primary electron-transfer rates, favouring one of the two, almost symmetrical pigment/protein branches, L and M. In this paper we explore the origins of this unidirectionality of electron transfer between the excited singlet state of the bacteriochlorophyll dimer (1 P∗) and the bacteriopheophytin (H) along the L protein subunit. Nonadiabatic electron-transfer theory is applied to analyze the asymmetry of the electron-transfer rates, k L and k M across the L and M branches. The asymmetry originates from the cumulative contributions of the nuclear Franck-Condon factor and the electronic coupling, both of which enhance the electron transfer rate across the L branch. The nuclear Frank-Condon factors are modified by the energy difference ΔE LM between the states P+ H− L and P+ H− M, which is induced by the electrostatic interactions of these ion-pair states with the protein polar groups, as well as by asymmetric Coulomb and medium polarization interactions. The computation results in ΔE LM=−(0.09±0.04) eV, which yields a nuclear enhancement contribution at 300 K of 1.5 (+ 0.8,− 0.3) to k L k M and therefore is insufficient to explain alone the observed asymmetry in reaction centers of Rps. viridis. Another contribution to the unidirectionality originates from electronic superexchange coupling for 1 P∗-BH via the virtual states of the accessory bacteriochlorophyll (B). The ratio of the intermolecular 1 P∗-B L and 1 P∗-B M electronic interaction terms was evaluated utilizing the tight-binding approximation with SCF-MO wavefunctions, together with the structural data for the prosthetic groups and for the polar amino acid side chains of the protein in reaction centers of Rps. viridis. The contribution to the enhancement of k L k M by the electronic superexchange is approx. 8±4. This asymmetry was traced to the combination of an excess negative charge density on the M-dimer component P M, together with structural asymmetry, which enhances the P M-B L electronic overlap. Consequently, the 1 P∗-B L-H L superexchange is favoured over the 1 P∗-B M-H M interaction. The combined effects of asymmetric nuclear Franck-Condon factors and electronic couplings yield a branching ratio of the electron-transfer rates along the two pigment branches in reaction centers of Rps. viridis of an approx. 12 (− 7,+ 15). This is sufficiently large to explain the experimentally observed unidirectionality.
来自球形红假单胞菌的分离光合反应中心的纳秒荧光。
DOI：
10.1016/0005-2728(84)90205-6
发表时间：
1984
期刊：
Biochimica et biophysica acta
影响因子：
--
作者：
Woodbury,NW;Parson,WW
通讯作者：
Parson,WW