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首页> 外文期刊>Biochemistry >Semiquinone-Iron Complex of Photosystem II: EPR Signals Assigned to the Low-Field Edge of the Ground State Doublet of Q_A~-Fe~(2+) and Q_B~-Fe~(2+)
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Semiquinone-Iron Complex of Photosystem II: EPR Signals Assigned to the Low-Field Edge of the Ground State Doublet of Q_A~-Fe~(2+) and Q_B~-Fe~(2+)

机译：光系统II的半醌-铁配合物：EPR信号分配给Q_A〜-Fe〜（2+）和Q_B〜-Fe〜（2+）基态双峰态的低场边缘

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摘要

The quinoneiron complex of the electron acceptor complex of Photosystem II was studied by EPR spectroscopy in Thermosynechococcus elongatus. New g ～ 2 features belonging to the EPR signal of the semiquinone forms of the primary and secondary quinone, i.e., Q _A~-Fe~(2+) and Q _B~-Fe~(2+), respectively, are reported. In previous studies, these signals were missed because they were obscured by the EPR signal arising from the stable tyrosyl radical, TyrD?. When the TyrD? signal wasremoved, either by chemical reduction or by the use of a mutant lacking TyrD, the new signals dominated the spectrum. For Q _A~-Fe~(2+), the signal was formed by illumination at 77 K or by sodium dithionite reduction in the dark. For Q _B~-Fe~(2+), the signal showed the characteristic period-of-two variations in its intensity when generated by a series of laser flashes. The new features showed relaxation characteristics comparable to those of the well-known features of the semiquinone-iron complexes and showed a temperature dependence consistent with an assignment to the low-field edge of the ground state doublet of the spin system. Spectral simulations are consistent with this assignment and with the currentmodel of the spin system. The signal was also present inQ _B~-Fe~(2+) in plant Photosystem II, but in plants, the signal was not detected in the Q _A~-Fe~(2+) state.
机译：通过EPR光谱在长嗜热球菌中研究了Photosystem II的电子受体配合物的醌铁配合物。据报道，新的g〜2特征分别属于伯醌和仲醌的半醌形式的EPR信号，即Q _A〜-Fe〜（2+）和Q _B〜-Fe〜（2+）。在以前的研究中，这些信号被遗漏了，因为它们被稳定的酪氨酰基基团TyrDβ产生的EPR信号所掩盖。当TyrD？通过化学还原或使用缺少TyrD的突变体去除了信号，新信号主导了光谱。对于Q_A〜-Fe〜（2+），信号是通过在77 K下照明或在黑暗中通过连二亚硫酸钠还原而形成的。对于Q _B〜-Fe〜（2+），当由一系列激光闪光产生时，信号在强度上表现出特征性的两周期变化。新的特征显示出与半醌-铁络合物的公知特征相当的弛豫特性，并且显示出与自旋系统基态双峰的低场边缘的分配一致的温度依赖性。光谱模拟与此分配和自旋系统的当前模型一致。该信号也存在于植物光系统II中的Q _B〜-Fe〜（2+）中，但在植物中，在Q _A〜-Fe〜（2+）状态下未检测到该信号。

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