Mitsuhashi Koji, Tamura Hiroyuki, Saito Keisuke, Ishikita Hiroshi
Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan.
Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan.
J Phys Chem B. 2021 Mar 25;125(11):2879-2885. doi: 10.1021/acs.jpcb.0c10885. Epub 2021 Mar 10.
Photosystem I has two active electron-transfer pathways. However, electron transfer occurs primarily along one of the two branches (A-branch) irrespective of the similar protein environments. Here, we report the origin of the A-branch electron transfer, considering the electronic coupling of the pigments and the electrostatic interaction with the protein environments. In the chlorophyll pair [PP], the electronic coupling between P and P is large (85 meV) for the highest occupied molecular orbital, forming the electronically coupled dimer [PP] and serving as an initial electron donor. In contrast, the coupling for the lowest unoccupied molecular orbital is small (15 meV), leading to charge transfer from P to P upon the [PP] excitation. The electronic coupling between [PP] and the accessory chlorophyll in the A-branch is significantly larger than that in the B-branch. These results indicate that the asymmetry of the electron-transfer activity originates from P as a chlorophyll epimer.
光系统I有两条活跃的电子传递途径。然而，无论蛋白质环境相似与否，电子传递主要沿着两条分支之一（A分支）发生。在此，我们考虑色素的电子耦合以及与蛋白质环境的静电相互作用，报告A分支电子传递的起源。在叶绿素对[PP]中，对于最高占据分子轨道，P和P之间的电子耦合很大（85毫电子伏），形成电子耦合二聚体[PP]并作为初始电子供体。相比之下，最低未占据分子轨道的耦合很小（15毫电子伏），导致在[PP]激发时电荷从P转移到P。A分支中[PP]与辅助叶绿素之间的电子耦合明显大于B分支中的电子耦合。这些结果表明，电子传递活性的不对称性源于作为叶绿素差向异构体的P。
