The reactivity of the S3 and S2 states towards NO and NH2OH was studied and compared using the period-4 oscillations in the F0-value induced by a train of single turnover Xenon flashes spaced 100 ms apart to monitor the reaction kinetics. The flash frequency also determined the time resolution of the assay, i.e. 100 ms. The S2 and S3-states were created by one and two single turnover pre-flashes, respectively. The NO concentration-dependence of the S3-decay indicated that at low NO-concentrations an S2-state was formed as an intermediate, whereas at higher concentrations a seemingly monophasic decay to the S1-state was observed. The sigmoidal concentration dependence indicated that a fast interaction of the S3-state with (at least) two NO-molecules is necessary for the fast S3 to S1 decay (τ ~0.4 s at 1.2 mM NO). The pH-dependence of the S3-decay suggests that a protonation reaction (pK ~6.9) is involved in the S3 to S1 decay. At intermediate NO-concentrations the protonation is only partially rate limiting, since the pH effect is more pronounced at high compared to intermediate NO-concentrations. A comparison of the reactivity of NO and hydroxylamine suggests that hydroxylamine reacts more efficiently with the S1 and S2 states, whereas NO reacts more efficiently with the S3-state. Based on our present knowledge of the oxygen evolving complex a possible reaction mechanism is proposed for the interaction between NO and the S3 state.

中文翻译：

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NO与光系统II析氧配合物的S2和S3-态相互作用的动力学表征

研究和比较了S3和S2态对NO和NH2OH的反应性，并使用了一系列间隔为100 ms的单次氙气闪光引起的F0值的周期4振荡进行比较，以监测反应动力学。闪烁频率还确定了测定的时间分辨率，即100毫秒。S2和S3状态分别由一个和两个单周转预闪创建。S3-衰变的NO浓度依赖性表明，在低NO-浓度下，形成S2-态作为中间体，而在更高浓度下，观察到单相衰减至S1-态。S形浓度依赖性表明，S3状态与（至少）两个NO分子的快速相互作用对于S3到S1的快速衰减是必要的（在1.2 mM NO下为τ〜0.4 s）。S3衰变的pH依赖性表明S3至S1的衰变涉及质子化反应（pK〜6.9）。在中等NO浓度下，质子化仅部分限制速率，因为与中等NO浓度相比，pH值在较高的情况下更为明显。NO和羟胺反应性的比较表明，羟胺与S1和S2状态的反应更有效，而NO与S3-状态的反应更有效。基于我们目前对氧释放复合物的了解，提出了一种可能的反应机理，用于NO和S3状态之间的相互作用。因为与中等浓度的NO相比，pH值在高浓度下更为明显。NO和羟胺反应性的比较表明，羟胺与S1和S2状态的反应更有效，而NO与S3-状态的反应更有效。基于我们目前对氧释放复合物的了解，提出了一种可能的反应机理，用于NO和S3状态之间的相互作用。因为与中等浓度的NO相比，pH值在高浓度下更为明显。NO和羟胺反应性的比较表明，羟胺与S1和S2状态的反应更有效，而NO与S3-状态的反应更有效。基于我们目前对氧释放复合物的了解，提出了一种可能的反应机理，用于NO和S3状态之间的相互作用。