德国柏林自由大学Dau, Holger团队报道了光合氧进化的电子-质子瓶颈。相关研究成果发表在2023年5月3日出版的《自然》。

光合作用通过以化学形式储存太阳能来为地球上的生命提供燃料。今天的富氧大气是由于光合作用过程中光系统II的蛋白质结合锰簇处的水分解而产生的。分子氧的形成始于一个有四个累积电子空穴的状态，即半个世纪前假设的S4状态，但在很大程度上仍未表征。

该文中，研究人员分析了光合O₂形成的这一关键阶段及其关键的机制作用。研究人员用微秒红外光谱跟踪了230000个暗适应光系统的激发周期。将这些结果与计算化学相结合，揭示了一个关键的质子空位是通过门控侧链去质子化最初产生的。随后，在单电子、多质子转移事件中形成活性氧自由基。这是光合O₂形成过程中最慢的一步，具有中等的能量屏障和显著的熵减缓。研究人员将S4状态确定为氧自由基状态；其形成之后是快速的O–O键合和O₂释放。

结合之前在实验和计算研究方面的突破，出现了一幅引人注目的光合O₂形成的原子图。研究结果为过去30亿年中可能没有变化的生物过程提供了见解，研究人员认为这将支持基于知识的人工分水系统设计。

附：英文原文

Title: The electron–proton bottleneck of photosynthetic oxygen evolution

Author: Greife, Paul, Schnborn, Matthias, Capone, Matteo, Assuno, Ricardo, Narzi, Daniele, Guidoni, Leonardo, Dau, Holger

Issue&Volume: 2023-05-03

Abstract: Photosynthesis fuels life on Earth by storing solar energy in chemical form. Today’s oxygen-rich atmosphere has resulted from the splitting of water at the protein-bound manganese cluster of photosystem II during photosynthesis. Formation of molecular oxygen starts from a state with four accumulated electron holes, the S4 state—which was postulated half a century ago1 and remains largely uncharacterized. Here we resolve this key stage of photosynthetic O2 formation and its crucial mechanistic role. We tracked 230,000 excitation cycles of dark-adapted photosystems with microsecond infrared spectroscopy. Combining these results with computational chemistry reveals that a crucial proton vacancy is initally created through gated sidechain deprotonation. Subsequently, a reactive oxygen radical is formed in a single-electron, multi-proton transfer event. This is the slowest step in photosynthetic O2 formation, with a moderate energetic barrier and marked entropic slowdown. We identify the S4 state as the oxygen-radical state; its formation is followed by fast O–O bonding and O2 release. In conjunction with previous breakthroughs in experimental and computational investigations, a compelling atomistic picture of photosynthetic O2 formation emerges. Our results provide insights into a biological process that is likely to have occurred unchanged for the past three billion years, which we expect to support the knowledge-based design of artificial water-splitting systems.

DOI: 10.1038/s41586-023-06008-5

Source: https://www.nature.com/articles/s41586-023-06008-5