The interaction of ammonia with the photosynthetic oxygen-evolving system
The interaction of ammonia with the photosynthetic oxygen-evolving system
复制标题
氨与光合放氧系统的相互作用
DOI：
10.1016/0005-2728(88)90011-4
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发表时间：
1988
期刊：
影响因子：
--
通讯作者：
K. Schenck
中科院分区：
文献类型：
--
作者：
L. Andréasson;Ö. Hansson;K. Schenck
用电子顺磁共振研究了氨气与析氧体系的反应。发现了两个具有不同结合特性的位点。以前已知的负责用氨修饰来自S2状态的多线EPR信号的一个位点被发现也结合了处于S1状态的氨，尽管较弱，但被认为只有在这种状态下才能访问。通过结合氨对g=4.1EPR信号形状和位置的影响，第二个结合部位也被发现在S1和S2状态下都是可访问的。测定了氨在S1和S2两个位置上的表观离解常数。在这两种状态下，氨的结合都不能解释观察到的氧释放的抑制，这表明与其他S态的结合在这种抑制中起着重要作用。已知的氯干扰氨诱导的放氧抑制，被发现在与g=4.1 EPR信号改变相关的位置与氨竞争。在用氨修饰多线EPR信号后，仍能观察到在17O标记水存在下的多线EPR信号的超精细线条的加宽。这表明在S2状态下，氨并没有完全取代结合在催化中心上的水。结合研究的结果按照两态两位点模型解释，其中两种状态分别由EPR信号识别，多线和g=4.1信号，两位点由氨对这些信号的影响识别，两态之间的平衡由配体与位点的结合来调节。
The reaction of ammonia with the oxygen-evolving system was investigated using EPR. Two sites with distinct binding properties were found. One site, previously known to be responsible for the modification by ammonia of the multiline EPR signal from the S2state and believed to be accessible in this state only, was found to bind ammonia also in the S1state although weaker. The second binding site, identified by the effect of bound ammonia on the shape and position of theg= 4.1 EPR signal, was also found to be accessible in both the S1and S2states. The apparent dissociation constants for ammonia at the two sites in the S1and S2states were determined. In neither state did the binding the ammonia account for the observed inhibition of oxygen evolution, suggesting that binding to other S states plays an important role in the inhibition. Chloride, which is known to interfere with ammonia-induced inhibition of oxygen evolution, was found to compete with ammonia at the site associated with the modification of theg= 4.1 EPR signal. The broadening of the hyperfine lines of the multiline EPR signal, seen in the presence of17O-labeled water, was still observed after the modification of the signal by ammonia. This indicates that ammonia has not completely displaced water bound to the catalytic site in the S2state. The results of the binding studies are interpreted in terms of a two state — two site model, where the two states are identified by their EPR signals, the multiline and theg= 4.1 signal, respectively, and the two sites identified by the effects of ammonia on these signals and where the equilibrium between the two states is regulated by the binding of ligands to the sites.