Krysiak Sonia, Burda Kvetoslava
Faculty of Physics and Applied Computer Science, AGH University of Krakow, al. Mickiewicza 30, 30-059 Krakow, Poland.
Curr Issues Mol Biol. 2024 Jul 8;46(7):7187-7218. doi: 10.3390/cimb46070428.
The oxygen evolution within photosystem II (PSII) is one of the most enigmatic processes occurring in nature. It is suggested that external proteins surrounding the oxygen-evolving complex (OEC) not only stabilize it and provide an appropriate ionic environment but also create water channels, which could be involved in triggering the ingress of water and the removal of O and protons outside the system. To investigate the influence of these proteins on the rate of oxygen release and the efficiency of OEC function, we developed a measurement protocol for the direct measurement of the kinetics of oxygen release from PSII using a Joliot-type electrode. PSII-enriched tobacco thylakoids were used in the experiments. The results revealed the existence of slow and fast modes of oxygen evolution. This observation is model-independent and requires no specific assumptions about the initial distribution of the OEC states. The gradual removal of exogenous proteins resulted in a slowdown of the rapid phase (ms) of O release and its gradual disappearance while the slow phase (tens of ms) accelerated. The role of external proteins in regulating the biphasicity and efficiency of oxygen release is discussed based on observed phenomena and current knowledge.
光系统II（PSII）中的氧气释放是自然界中最神秘的过程之一。有人认为，围绕放氧复合体（OEC）的外部蛋白质不仅能使其稳定并提供合适的离子环境，还能形成水通道，这可能参与触发水的进入以及将氧和质子从系统中排出。为了研究这些蛋白质对氧气释放速率和OEC功能效率的影响，我们开发了一种测量方案，使用乔利奥型电极直接测量PSII中氧气释放的动力学。实验中使用了富含PSII的烟草类囊体。结果揭示了氧气释放存在慢速和快速模式。这一观察结果与模型无关，且无需对OEC状态的初始分布做出特定假设。外源蛋白质的逐渐去除导致O释放快速阶段（毫秒）减缓并逐渐消失，而慢速阶段（几十毫秒）加速。基于观察到的现象和现有知识，讨论了外部蛋白质在调节氧气释放的双相性和效率方面的作用。
