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化学学报
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化学学报 ›› 2001, Vol. 59 ›› Issue (4): 456-465. 上一篇    下一篇

研究论文

光合反应中心原初电子转移机理的理论研究

张小东;张纯喜;马淑华;徐红;沈玲玲;李良璧;张兴康;匡廷云;张启元   

  1. 中国科学院化学研究所.北京(100080);中国科学院分子科学中心分子动态与稳 态国家重点实验室;中国科学院植物研究所.北京(100044);中国科学院光合作用 开放实验室
  • 发布日期:2001-04-15

The theoretical studies on the machanism of the primary electron transfer in the photosynthetic reaction center

Zhang Xiaodong;Zhang Chunxi;Ma Shuhua;Xu Hong;Shen Lingling;Li Liangbi;Zhang Xingkang;Kuang Tingyun;Zhang Qiyuan   

  1. Inst of Chem, CAS.Beijing(100080);Inst of Botany, CAS.Beijing(100044)
  • Published:2001-04-15

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用量子化学密度泛函B3LYP方法在3-21G水平上计算细菌光合反应中心原初电子给体P960和绿色植物PSⅡ光合反应中心原初电子给体P680的电子结构，然后研究轴向配位的组氨酸残基和周围蛋白质环境的影响，最后探讨其原初电子转移机理。计算结果表明：(1)细菌光合作用反应中心原初电子给体P960-h的HOMO主要是由与M分支相连的组成单元上原子的原子轨道组成，而它的LUMO则两个组成单元上原子的原子轨道都有贡献；PSⅡ反应中心中原初电子给体P680的HOMO和LUMO均主要由与D1蛋白相连的组成单元上原子的原子轨道组成。这些计算结果能够从反应中心最核心的部分-原初电子给体的电子结构方面解释Rps.uiridis反应中心和PSⅡ反应中心原初电子转移只沿一个分支进行的的途径选择性。(2)虽然与细菌反应中心原初电子给体超分子P960的两个细菌叶绿素分子形成轴向配位的组氨酸残基His并未参与超分子P960-h的HOMO和LUMO的组成，但是由于其轴向配位，使得P960-h的ELUMO显著地升高到高于辅助细菌叶绿素和去镁细菌叶绿素的相应值，使得原初电子转移反应能够顺利进行。否则原初电子转移反应很难进行。PSⅡ反应中心的情况，与细菌反应中心十分相似。(3)细菌反应中心辅助细菌叶绿素(ABChlb)中的Mg离子与最近的组氨酸残基His中的N原子的距离和原初电子给体P960中的相应的Mg-N的距离相似，因此同样应该考虑此轴向配位的组氨酸残基，此时原初电子转移反应是沿L分支从P960-h经ABChlb到去镁细菌叶绿素(BPheob)的两步电子转移过程。而PSⅡ反应中心的辅助叶绿素不存在His的轴向配位，这应是与细菌反应中心的重要区别之一，此时原初电子转移应是沿Dl分支从P680-h到Pheoa的一步电子转移过程，但同时也不能完全排除从P680-h到AChla到Pheoa的二步电子转移过程。

关键词: 光合反应, 电子转移, 电子结构, 密度泛函理论

The electron structure of teh primary electron donor P960 in Rhodopseuodomonas (Rps.) uiridis photosynthetic reaction center (RC) and P680 in photosystem Ⅱ (PSⅡ) RC have been studied with B3LYP DFT quantum chemical ab initio method at 3-21G level. The influence of the surrounding proterins and the axial coordination of histindine residues on the electronic structure of the primary electron donor has also been studied. Finally, the mechanism of the primary electron transfer (ET) is discussed. The results indicate: (1) the HOMO of super-molecule P960 - h in bacerial RC mainly consists of atomic orbitalsof atoms lacated at the composition unit M. The corresponding LUMO mainly consists of atomic orbitals of atoms located at both L and M composition units. Both HOMO and LUMO of super-molecule P680-h in PSⅡ RC mainly consist of atomic orbitals of atoms located at composition unit Dl. These calculated results are helpful for understanding the experimental fact that the primary ET in RC of bacterial and PSⅡ mainly perform along L branch and D1 branch, respectively. (2) Although the His residues, which are axially coordinated to teh primary electron donor P960 in the bacterial RC, do not contribute to the compositions of HOMO and LUMO of super-molecule P960-h, they make the ELUMO of P960-h much greater than that of P960 and greater than those of ABChl and BPheo. This cause the primary ET in bacterial RC to proceed easily. Otherwise, it will be very difficult for the primary ET to perform. For PSⅡ RC, the case is similar. (3) The distance between the Mg ion in ABChl and the N in the His residues is similar to that between the Mg ion in P960 and the N atom in the corresponding His, so that the His residues coordinating to ABChl must be taken into consideration. At this condition, the primary ET in bacterial RC should be a two-step ET process form P960-h to BPheo bL via ABChl bL^h along the L branch. For PSⅡ RC, there does not exist the axial coordination of His to accessory 光合反应中心原初电子转移机理的理论研究

Key words: ELECTRONIC STRUCTURE

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