Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira-2-1-1, Aobaku, Sendai 980-8577, Japan.
J Am Chem Soc. 2011 Mar 30;133(12):4655-60. doi: 10.1021/ja2000566. Epub 2011 Mar 7.
The oxidation of a redox-active tyrosine residue Y(Z) in photosystem II (PSII) is coupled with proton transfer to a hydrogen-bonded D1-His190 residue. Because of the apparent proximity of Y(Z) to the water-oxidizing complex and its redox activity, it is believed that Y(Z) plays a significant role in water oxidation in PSII. We investigated the g-anisotropy of the tyrosine radical Y(Z)(•) to provide insight into the mechanism of Y(Z)(•) proton-coupled electron transfer in Mn-depleted PSII. The anisotropy was highly resolved by electron paramagnetic resonance spectroscopy at the W-band (94.9 GHz) using PSII single crystals. The g(X)-component along the phenolic C-O bond of Y(Z)(•) was calculated by density functional theory (DFT). It was concluded from the highly resolved g-anisotropy that Y(Z) loses a phenol proton to D1-His190 upon tyrosine oxidation, and D1-His190 redonates the same proton back to Y(Z)(•) upon reduction.
在光系统 II（PSII）中，氧化还原活性酪氨酸残基 Y(Z)与质子转移到氢键结合的 D1-His190 残基相耦合。由于 Y(Z)与水氧化复合物的明显接近及其氧化还原活性，人们认为 Y(Z)在 PSII 中的水氧化中起着重要作用。我们研究了酪氨酸自由基 Y(Z)(•)的 g 各向异性，以深入了解 Mn 耗尽 PSII 中 Y(Z)(•)质子耦合电子转移的机制。使用 PSII 单晶，通过在 W 波段（94.9 GHz）的电子顺磁共振波谱学高度解析了各向异性。通过密度泛函理论（DFT）计算了 Y(Z)(•)的酚 C-O 键上的 g(X)分量。从高度解析的 g 各向异性得出结论，Y(Z)在酪氨酸氧化时向 D1-His190 失去一个苯酚质子，而 D1-His190 在还原时将相同的质子重新捐赠给 Y(Z)(•)。
