Hasegawa Koji, Kimura Yukihiro, Ono Taka-aki
Laboratory for Photo-Biology (I), RIKEN Photodynamics Research Center, The Institute of Physical and Chemical Research, 519-1399 Aoba, Aramaki, Aoba, Sendai 980-0845, Japan.
Biophys J. 2004 Feb;86(2):1042-50. doi: 10.1016/S0006-3495(04)74179-X.
Cl(-) is an indispensable cofactor for photosynthetic O(2) evolution and is functionally replaced by NO(3)(-). Structural changes of an isotopically labeled NO(3)(-) ion, induced by the oxidation of the Mn cluster (S(1)-to-S(2)), were detected by FTIR spectroscopy. NO(3)(-)-substituted photosystem II core particles showed (14)N(16)O(3)(-)/(15)N(16)O(3)(-) and (14)N(16)O(3)(-)/(14)N(18)O(3)(-) isotopic bands in the S(2)/S(1) spectra with markedly high signal/noise ratio. These bands appeared only in the region from 1415 to 1284 cm(-1), indicating that the bands do not arise from a metal-bound NO(3)(-) but from an ionic NO(3)(-). The intensity of the bands exhibited a quantitatively proportional relationship with the O(2) activity. These results demonstrate that the NO(3)(-) functionally bound to the Cl(-) site couples to the Mn cluster structurally, but is not associated with the cluster as a direct ligand. Comparison of the bands for two isotopes ((15)N and (18)O) and their simulations enable us to assign each band to the S(1) and S(2) states. The results indicate that the NO(3)(-) ion bound to the Cl(-) site is highly asymmetric in S(1) but rather symmetric in S(2). Since NO(3)(-) functionally replaces Cl(-), most of the conclusions drawn from this study will be also applicable to Cl(-).
Cl(-) 是光合放氧过程中不可或缺的辅助因子，其功能可被 NO(3)(-) 替代。通过傅里叶变换红外光谱（FTIR）检测到，锰簇氧化（从 S(1) 到 S(2)）诱导的同位素标记的 NO(3)(-) 离子的结构变化。用 NO(3)(-) 取代的光系统 II 核心颗粒在 S(2)/S(1) 光谱中显示出 (14)N(16)O(3)(-)/(15)N(16)O(3)(-) 和 (14)N(16)O(3)(-)/(14)N(18)O(3)(-) 同位素带，其信噪比明显很高。这些带仅出现在 1415 至 1284 cm(-1) 区域，表明这些带并非来自与金属结合的 NO(3)(-)，而是来自离子型 NO(3)(-)。这些带的强度与 O(2) 活性呈现定量比例关系。这些结果表明，功能上与 Cl(-) 位点结合的 NO(3)(-) 在结构上与锰簇耦合，但并非作为直接配体与该簇相关联。对两种同位素（(15)N 和 (18)O）的谱带及其模拟结果进行比较，使我们能够将每个谱带归属于 S(1) 和 S(2) 状态。结果表明，与 Cl(-) 位点结合的 NO(3)(-) 离子在 S(1) 状态下高度不对称，而在 S(2) 状态下相当对称。由于 NO(3)(-) 在功能上取代了 Cl(-)，本研究得出的大多数结论也将适用于 Cl(-)。
