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光系统Ⅱ(PSⅡ)次级电子给体TyrZ担负调控原初电荷分离和水的催化氧化功能.目前有两类TyrZ调控机理模型被提出:一类是TyrZ通过与底物水分子直接作用调控水氧化;另一类是TyrZ处于疏水环境中,不与底物水分子直接作用,而是借助与His190之间氢键强度的变化调控水氧化.本文利用低温电子顺磁共振技术研究与水分子类似的甲醇分子对活性PSⅡ中TyrZ氧化还原特性的影响,发现当Mn簇处于S2和S0态时,甲醇分子的存在能够明显促进TyrZ的低温氧化和TyrZ·的低温还原.理论计算显示:(1)当甲醇分子与Tyr直接作用时会导致Tyr氧化变难;(2)伴随环境极性降低,Tyr的氧化变得容易.综合这些结果,我们推测在活性PSⅡ中甲醇分子不与TyrZ直接作用,甲醇对TyrZ的低温氧化及TyrZ·的低温还原的促进作用可能是由于甲醇分子替换PSⅡ内部的水分子,降低了TyrZ-His190周围环境的极性,使TyrZ与His190之间的氢键强度增加所致.鉴于甲醇分子与水的类似性,以上结果支持我们最近提出的活性PSⅡ中TyrZ不与水分子直接作用的观点.
TyrZ, a secondary electron donor of photosystem Ⅱ (PSⅡ), plays a role in the control of primary charge separation and catalytic oxidation of water.At present, two types of TyrZ regulation mechanisms are proposed: one is that TyrZ regulates water oxidation through the direct interaction with substrate water molecules ; The other is that TyrZ is in a hydrophobic environment and does not directly interact with the substrate water molecules, but rather regulates water oxidation through changes in the hydrogen bond strength with His 190. In this paper, low temperature electron paramagnetic resonance is used to study water molecules Methanol molecules on the redox properties of TyrZ in active PSⅡ. It was found that the presence of methanol molecules can significantly promote the low-temperature oxidation of TyrZ and the reduction of TyrZ · when Mn clusters are in S2 and S0 states. The theoretical calculations show that: (1) when The direct oxidation of methanol molecules to Tyr results in the oxidation of Tyr becoming more difficult. (2) The oxidation of Tyr becomes easier with the reduction of environmental polarity. Combining these results, we speculate that methanol molecules do not directly interact with TyrZ in active PSII, The promotion of TyrZ’s low temperature oxidation and TyrZ · low temperature reduction may be due to the replacement of water molecules within the PSII by methanol molecules and the decrease of the polarity of the TyrZ-His190 environment, which makes TyrZ and His190 The strength of hydrogen bonds increased. Given the similarity of methanol and water molecules, these results support our active PSⅡ recently proposed TyrZ not act directly on the water molecules of view.