Competitive binding of acetate and chloride in photosystem II
Competitive binding of acetate and chloride in photosystem II
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DOI：
10.1021/bi990341t
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发表时间：
1999-05-18
期刊：
影响因子：
2.9
通讯作者：
Brudvig, GW
中科院分区：
文献类型：
--
作者：
Kühne, H;Szalai, VA;Brudvig, GW
氯离子和乙酸根与光系统II（PSII）的结合被检查，以阐明乙酸根抑制的机制。的抑制模式进行了研究，并通过稳态O-2进化测量与电子顺磁共振（EPR）结果相关的个人结合位点进行了分配。两个结合位点被发现乙酸，一个氯敏感的电子供体侧和一个氯不敏感的电子受体侧。相应的结合常数如下：K-Cl = 0.5 +/-0.2mM（氯离子与供体侧结合），K-I = 16 +/-5mM（乙酸根与供体侧结合），K-I' = 130 +/-40mM（乙酸根与受体侧结合）。当乙酸结合到PSII的受体侧时，200 K光照诱导了窄化形式的Q（A）-Fe-II EPR信号，其产率与氯离子浓度无关。当乙酸结合到供体侧时，室温照射产生S2 Yz。状态EPR测量结果表明，无论是产量和形成速率的这种状态增加与乙酸浓度，增加氯离子浓度减慢的速度形成的S2 Yz。状态，但不影响S2 Yz的稳态产率。状态这些结果表明，光诱导的反应在乙酸抑制PSII中受到乙酸的供体侧和受体侧结合的调节，而S2 Yz（.）用于EPR测量的高PSII浓度下的状态主要取决于受体侧周转。我们的数据进一步支持氯化物与Y-z（.）的紧密接近，表明氯离子在O-2-释放复合物的电子转移机制中可能起作用。
The binding of chloride and acetate to photosystem ii (PSII) was examined to elucidate the mechanism of acetate inhibition. The mode of inhibition was studied, and individual binding sites were assigned by steady-state O-2 evolution measurements in correlation with electron paramagnetic resonance (EPR) results. Two binding sites were found for acetate, one chloride-sensitive on the electron donor side and one chloride-insensitive on the electron acceptor side. The respective binding constants were as follows: K-Cl = 0.5 +/- 0.2 mM (chloride binding to the donor side), K-I = 16 +/- 5 mM (acetate binding to the donor side), and K-I' = 130 +/- 40 mM (acetate binding to the acceptor side). When acetate was bound to the acceptor side of PSII, 200 K illumination induced a narrowed form of the Q(A)-Fe-II EPR signal, the yield of which was independent of the chloride concentration. When acetate was bound to the donor side, room-temperature illumination produced the S2Yz. state. EPR measurements showed that both the yield and formation rate of this state increased with acetate concentration, increasing chloride concentrations slowed the rate of formation of the S2Yz. state, but did not affect the steady-state yield of the S2Yz. state. These findings indicate that the light-induced reactions in acetate-inhibited PSII are modulated by both donor side and acceptor side binding of acetate, while the steady-state yield of the S2Yz(.) state at the high PSII concentrations used for EPR measurements depends primarily on acceptor side turnover. Our data further support a close proximity of chloride to Y-z(.), indicating a possible role for chloride in the electron transfer mechanism at the O-2-evolving complex.