光系统Ⅱ水氧化机制的研究进展  

Advances in the mechanism of water oxidation in photosystem Ⅱ

作　　者：田祎祎 刘瑞苑 路慧哲[1] TIAN Yi-yi;LIU Rui-yuan;LU Hui-zhe(College of Science,China Agricultural University,Beijing 100193,China)

机构地区：[1]中国农业大学理学院,北京100193

出　　处：《分子科学学报》2023年第6期471-478,共8页Journal of Molecular Science

基　　金：国家重点研发计划资助项目(2021YFD1700102)。

摘　　要：光系统Ⅱ(PSⅡ)的水氧化机制对于揭示光合作用的奥秘和促进人工光合的发展具有重要意义,但由于目前还不能通过实验确定处于S_(4)态的Mn_(4)CaO_(5)释放氧气的确切机制,因此该机制长期以来广受关注.自Kok循环模型提出后,PSⅡ的水氧化机制研究取得了巨大的进展.本文首先介绍了光合作用和PSⅡ的整体结构、PSⅡ的放氧复合物(OEC)、电子传递链及Kok循环,其次重点概述了目前几种广为人知的水氧化机制假设,包括“水亲核进攻”机制(WNA)、“自由基耦合”机制(RC)、“亲核氧-氧耦合”机制(NOOC)以及“双通道”机制,以期为后续PSⅡ水氧化机制研究和人工光合研究提供参考.PhotosystemⅡ(PSⅡ)is a multi-subunit protein complex embedded in the thylakoid membranes of oxygenic photosynthetic organisms.It captures the energy of visible-light photons,powering water oxidization catalysis at the oxygen-evolving complex(OEC)and reduction of plastoquinone at the Q_(B) site.The oxygen-evolving complex,composed of a Mn_(4)CaO_(5) cluster surrounded by water and amino acid ligands,acts as a highly efficient water oxidation catalyst which experiences five“S-states”during a light-driven reaction cycle.The most significant structural feature of the Mn_(4)CaO_(5) cluster,which may be important for elucidating the mechanism of the water oxidation reaction,is its distorted chair form.The research on the mechanism of water oxidation in photosystemⅡis of great significance for understanding the mysteries of natural photosynthesis and for the development of artificial photosynthesis.Here,we review several main water oxidation mechanisms,in order to provide some references for the subsequent exploration of water oxidation mechanisms and the development of oxygen evolution materials.By constructing a hybrid quantum mechanics/molecular mechanics(QM/MM)model of PSⅡ,Eduardo proposed the water“water nucleophilic attack”(WNA)mechanism based on the change of oxidation state,protonation state and structural rearrangement of Mn_(4)CaO_(5) during the whole Kok cycle.However,subsequent X-ray free electron laser(XFEL)experiments and electron paramagnetic resonance(EPR)spectroscopy supported that there is only the opened-cubane structure(S_(3)^(A,W))of the Mn_(4)CaO_(5),indicating that water oxidation in PSⅡis impossible through the WNA mechanism.The“radical coupling”(RC)mechanism,which relies on opened-cubane structure(S_(4)^(A,W))of the Mn_(4)CaO_(5)with the Mn^(Ⅳ)(1)-O·entity as the key starting structure,has been tested by evolving computational and experimental results since it was proposed.EPR spectroscopy has recently identified that a water-unbound closed-cubane structure(S_(3)^(B,unbou

关 键 词：光系统Ⅱ 水氧化机制 “水亲核进攻”机制 “自由基耦合”机制 “亲核氧-氧耦合”机制 

分 类 号：O644[理学—物理化学]