Dekmak Mohamad Yahia, Mäusle Sarah M, Brandhorst Janosch, Simon Philipp S, Dau Holger
Department of Physics, Freie Universität Berlin, Berlin, Germany.
Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
Photosynth Res. 2024 Dec;162(2-3):353-369. doi: 10.1007/s11120-023-01057-3. Epub 2023 Nov 23.
In oxygen-evolving photosystem II (PSII), the multi-phasic electron transfer from a redox-active tyrosine residue (TyrZ) to a chlorophyll cation radical (P680) precedes the water-oxidation chemistry of the S-state cycle of the MnCa cluster. Here we investigate these early events, observable within about 10 ns to 10 ms after laser-flash excitation, by time-resolved single-frequency infrared (IR) spectroscopy in the spectral range of 1310-1890 cm for oxygen-evolving PSII membrane particles from spinach. Comparing the IR difference spectra at 80 ns, 500 ns, and 10 µs allowed for the identification of quinone, P680 and TyrZ contributions. A broad electronic absorption band assignable P680 was used to trace largely specifically the P680 reduction kinetics. The experimental time resolution was taken into account in least-square fits of P680 transients with a sum of four exponentials, revealing two nanosecond phases (30-46 ns and 690-1110 ns) and two microsecond phases (4.5-8.3 µs and 42 µs), which mostly exhibit a clear S-state dependence, in agreement with results obtained by other methods. Our investigation paves the road for further insight in the early events associated with TyrZ oxidation and their role in the preparing the PSII donor side for the subsequent water oxidation chemistry.
在放氧光系统II（PSII）中，从氧化还原活性酪氨酸残基（TyrZ）到叶绿素阳离子自由基（P680）的多相电子转移先于MnCa簇S态循环的水氧化化学过程。在这里，我们通过对菠菜放氧PSII膜颗粒在1310 - 1890 cm光谱范围内进行时间分辨单频红外（IR）光谱研究，来探究这些在激光闪光激发后约10 ns至10 ms内可观测到的早期事件。比较80 ns、500 ns和10 µs时的红外差分光谱，可确定醌、P680和TyrZ的贡献。一个可归属于P680的宽电子吸收带被用于主要特异性地追踪P680的还原动力学。在对P680瞬态进行四个指数之和的最小二乘拟合时考虑了实验时间分辨率，结果显示出两个纳秒阶段（30 - 46 ns和690 - 1110 ns）和两个微秒阶段（4.5 - 8.3 µs和42 µs），这些阶段大多呈现出明显的S态依赖性，这与其他方法得到的结果一致。我们的研究为进一步深入了解与TyrZ氧化相关的早期事件及其在为后续水氧化化学过程准备PSII供体侧中所起的作用铺平了道路。
