Marchiori David A, Oyala Paul H, Debus Richard J, Stich Troy A, Britt R David
Department of Chemistry, University of California, Davis , Davis, California 95616, United States.
Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, United States.
J Phys Chem B. 2018 Feb 8;122(5):1588-1599. doi: 10.1021/acs.jpcb.7b11101. Epub 2018 Jan 24.
The MnCaO oxygen-evolving complex (OEC) of photosystem II catalyzes the light-driven oxidation of two substrate waters to molecular oxygen. ELDOR-detected NMR along with computational studies indicated that ammonia, a substrate analogue, binds as a terminal ligand to the Mn4A ion trans to the O5 μ oxido bridge. Results from electron spin echo envelope modulation (ESEEM) spectroscopy confirmed this and showed that ammonia hydrogen bonds to the carboxylate side chain of D1-Asp61. Here we further probe the environment of OEC with an emphasis on the proximity of exchangeable protons, comparing ammonia-bound and unbound forms. Our ESEEM and electron nuclear double resonance (ENDOR) results indicate that ammonia substitutes for the W1 terminal water ligand without significantly altering the electronic structure of the OEC.
光系统II的MnCaO析氧复合物（OEC）催化两个底物水分子在光驱动下氧化为分子氧。电子双共振检测的核磁共振（ELDOR-detected NMR）以及计算研究表明，作为底物类似物的氨作为末端配体与O5μ氧化桥对面的Mn4A离子结合。电子自旋回波包络调制（ESEEM）光谱的结果证实了这一点，并表明氨与D1-Asp61的羧酸盐侧链形成氢键。在此，我们进一步探究OEC的环境，重点关注可交换质子的接近程度，比较氨结合形式和未结合形式。我们的ESEEM和电子核双共振（ENDOR）结果表明，氨替代了W1末端水配体，而没有显著改变OEC的电子结构。
