Photosynthetic water splitting by the Mn4Ca2+OX catalyst of photosystem II: its structure, robustness and mechanism.

IF 7.2 2区 生物学 Q1 BIOPHYSICS
James Barber
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引用次数: 13

Abstract

The biological energy cycle of our planet is driven by photosynthesis whereby sunlight is absorbed by chlorophyll and other accessory pigments. The excitation energy is then efficiently transferred to a reaction centre where charge separation occurs in a few picoseconds. In the case of photosystem II (PSII), the energy of the charge transfer state is used to split water into oxygen and reducing equivalents. This is accomplished by the relatively low energy content of four photons of visible light. PSII is a large multi-subunit membrane protein complex embedded in the lipid environment of the thylakoid membranes of plants, algae and cyanobacteria. Four high energy electrons, together with four protons (4H+), are used to reduce plastoquinone (PQ), the terminal electron acceptor of PSII, to plastoquinol (PQH2). PQH2 passes its reducing equivalents to an electron transfer chain which feeds into photosystem I (PSI) where they gain additional reducing potential from a second light reaction which is necessary to drive CO2 reduction. The catalytic centre of PSII consists of a cluster of four Mn ions and a Ca2+ linked by oxo bonds. In addition, there are seven amino acid ligands. In this Article, I discuss the structure of this metal cluster, its stability and the probability that an acid-base (nucleophilic-electrophilic) mechanism catalyses the water splitting reaction on the surface of the metal-cluster. Evidence for this mechanism is presented from studies on water splitting catalysts consisting of organo-complexes of ruthenium and manganese and also by comparison with the enzymology of carbon monoxide dehydrogenase (CODH). Finally the relevance of our understanding of PSII is discussed in terms of artificial photosynthesis with emphasis on inorganic water splitting catalysts as oxygen generating photoelectrodes.

光系统II中Mn4Ca2+OX催化剂的光合水分解:结构、稳健性和机理
我们星球的生物能量循环是由光合作用驱动的,通过光合作用,叶绿素和其他辅助色素吸收阳光。激发能然后有效地转移到反应中心,在那里电荷分离发生在几皮秒内。在光系统II (PSII)的情况下,电荷转移状态的能量被用来将水分解成氧和还原物。这是由四个可见光光子的相对较低的能量含量来完成的。PSII是一种大型多亚基膜蛋白复合物,嵌入在植物、藻类和蓝藻类囊体膜的脂质环境中。利用4个高能电子和4个质子(4H+)将PSII的末端电子受体plastoquinone (PQ)还原为plasoquinol (PQH2)。PQH2将其还原等价物传递给电子传递链,进入光系统I (PSI),在那里它们从第二次光反应中获得额外的还原电位,这是驱动二氧化碳还原所必需的。PSII的催化中心由四个Mn离子和一个由氧键连接的Ca2+组成。此外,还有7种氨基酸配体。在这篇文章中,我讨论了这种金属团簇的结构,它的稳定性和酸碱(亲核-亲电)机制在金属团簇表面催化水分裂反应的可能性。钌和锰有机配合物组成的水裂解催化剂的研究以及与一氧化碳脱氢酶(CODH)酶学的比较证明了这一机制。最后,从人工光合作用的角度讨论了我们对PSII的理解的相关性,重点讨论了无机水裂解催化剂作为产氧光电极的作用。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Quarterly Reviews of Biophysics
Quarterly Reviews of Biophysics 生物-生物物理
CiteScore
12.90
自引率
1.60%
发文量
16
期刊介绍: Quarterly Reviews of Biophysics covers the field of experimental and computational biophysics. Experimental biophysics span across different physics-based measurements such as optical microscopy, super-resolution imaging, electron microscopy, X-ray and neutron diffraction, spectroscopy, calorimetry, thermodynamics and their integrated uses. Computational biophysics includes theory, simulations, bioinformatics and system analysis. These biophysical methodologies are used to discover the structure, function and physiology of biological systems in varying complexities from cells, organelles, membranes, protein-nucleic acid complexes, molecular machines to molecules. The majority of reviews published are invited from authors who have made significant contributions to the field, who give critical, readable and sometimes controversial accounts of recent progress and problems in their specialty. The journal has long-standing, worldwide reputation, demonstrated by its high ranking in the ISI Science Citation Index, as a forum for general and specialized communication between biophysicists working in different areas. Thematic issues are occasionally published.
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