Kornienko Nikolay, Zhang Jenny Z, Sokol Katarzyna P, Lamaison Sarah, Fantuzzi Andrea, van Grondelle Rienk, Rutherford A William, Reisner Erwin
Department of Chemistry , University of Cambridge , Lensfield Road , Cambridge CB2 1EW , U.K.
Department of Life Sciences , Imperial College London, South Kensington Campus , London SW7 2AZ , U.K.
J Am Chem Soc. 2018 Dec 26;140(51):17923-17931. doi: 10.1021/jacs.8b08784. Epub 2018 Sep 24.
Protein film photoelectrochemistry has previously been used to monitor the activity of photosystem II, the water-plastoquinone photooxidoreductase, but the mechanistic information attainable from a three-electrode setup has remained limited. Here we introduce the four-electrode rotating ring disk electrode technique for quantifying light-driven reaction kinetics and mechanistic pathways in real time at the enzyme-electrode interface. This setup allows us to study photochemical HO oxidation in photosystem II and to gain an in-depth understanding of pathways that generate reactive oxygen species. The results show that photosystem II reacts with O through two main pathways that both involve a superoxide intermediate to produce HO. The first pathway involves the established chlorophyll triplet-mediated formation of singlet oxygen, which is followed by its reduction to superoxide at the electrode surface. The second pathway is specific for the enzyme/electrode interface: an exposed antenna chlorophyll is sufficiently close to the electrode for rapid injection of an electron to form a highly reducing chlorophyll anion, which reacts with O in solution to produce O. Incomplete HO oxidation does not significantly contribute to reactive oxygen formation in our conditions. The rotating ring disk electrode technique allows the chemical reactivity of photosystem II to be studied electrochemically and opens several avenues for future investigation.
蛋白质膜光电化学此前已被用于监测光系统II（水-质体醌光氧化还原酶）的活性，但从三电极装置中获得的机理信息仍然有限。在此，我们引入了四电极旋转环盘电极技术，用于实时定量酶-电极界面处的光驱动反应动力学和机理途径。这种装置使我们能够研究光系统II中的光化学羟基氧化反应，并深入了解产生活性氧的途径。结果表明，光系统II通过两条主要途径与氧气反应，这两条途径都涉及超氧化物中间体以产生羟基。第一条途径涉及已确定的叶绿素三线态介导的单线态氧形成，随后在电极表面将其还原为超氧化物。第二条途径是酶/电极界面特有的：一个暴露的天线叶绿素与电极足够接近，以便快速注入电子形成高度还原的叶绿素阴离子，该阴离子与溶液中的氧气反应生成超氧阴离子。在我们的条件下，不完全的羟基氧化对活性氧的形成没有显著贡献。旋转环盘电极技术使我们能够通过电化学方法研究光系统II的化学反应性，并为未来的研究开辟了几条途径。
