Department of Life Sciences, Imperial College London, Sir Ernst Chain Building, South Kensington Campus, London SW7 2AZ, UK.
Nat Plants. 2017 Apr 3;3:17041. doi: 10.1038/nplants.2017.41.
Sunlight is absorbed and converted to chemical energy by photosynthetic organisms. At the heart of this process is the most fundamental reaction on Earth, the light-driven splitting of water into its elemental constituents. In this way molecular oxygen is released, maintaining an aerobic atmosphere and creating the ozone layer. The hydrogen that is released is used to convert carbon dioxide into the organic molecules that constitute life and were the origin of fossil fuels. Oxidation of these organic molecules, either by respiration or combustion, leads to the recombination of the stored hydrogen with oxygen, releasing energy and reforming water. This water splitting is achieved by the enzyme photosystem II (PSII). Its appearance at least 3 billion years ago, and linkage through an electron transfer chain to photosystem I, directly led to the emergence of eukaryotic and multicellular organisms. Before this, biological organisms had been dependent on hydrogen/electron donors, such as HS, NH, organic acids and Fe, that were in limited supply compared with the oceans of liquid water. However, it is likely that water was also used as a hydrogen source before the emergence of PSII, as found today in anaerobic prokaryotic organisms that use carbon monoxide as an energy source to split water. The enzyme that catalyses this reaction is carbon monoxide dehydrogenase (CODH). Similarities between PSII and the iron- and nickel-containing form of this enzyme (Fe-Ni CODH) suggest a possible mechanism for the photosynthetic O-O bond formation.
阳光被光合生物吸收并转化为化学能。在这个过程的核心是地球上最基本的反应，即水的光驱动分解成其元素组成部分。通过这种方式，释放出分子氧，维持有氧大气并形成臭氧层。释放出的氢被用于将二氧化碳转化为构成生命的有机分子，这些有机分子也是化石燃料的起源。这些有机分子的氧化，无论是通过呼吸还是燃烧，都会导致储存的氢与氧重新结合，释放能量并重新形成水。这种水的分解是由酶光合系统 II（PSII）实现的。它至少在 30 亿年前出现，并通过电子传递链与光合系统 I 相连，直接导致真核生物和多细胞生物的出现。在此之前，生物有机体一直依赖于氢/电子供体，如 HS、NH、有机酸和 Fe，与液态水相比，这些供体的供应是有限的。然而，在 PSII 出现之前，水也可能被用作氢源，就像今天在使用一氧化碳作为能源来分解水的厌氧原核生物中发现的那样。催化这一反应的酶是一氧化碳脱氢酶（CODH）。PSII 和这种酶的铁和镍形式（Fe-Ni CODH）之间的相似性表明了光合作用 O-O 键形成的可能机制。
