Ono T, Inoue Y
Solar Energy Research Group, Institute of Physical and Chemcial Research (RIKEN), Saitama, Japan.
Arch Biochem Biophys. 1989 Dec;275(2):440-8. doi: 10.1016/0003-9861(89)90390-1.
The properties of the S2 states formed in Ca2+-extracted, Sr2+-substituted, and Cd2+-substituted photosystem II (PSII) were comparatively studied by means of thermoluminescence (TL) and low temperature EPR spectroscopy. The following results were obtained: (i) Ca-extracted PSII showed neither EPR multiline nor g = 4.1 signals but showed an abnormal TL band with an upshifted peak temperature, which did not oscillate on excitation with two or more flashes. Addition of Ca2+ to the extracted PSII reversed most of these effects concomitant with marked restoration of O2 evolution, but the EPR g = 4.1 signal remained lost. (ii) Sr2+ substitution largely restored the g = 4.1 signal and partly restored the multiline signal in a modified form having a reduced hyperfine line spacing concomitant with partial restoration of O2 evolution. Sr2+ substitution also reversed the abnormal TL peak temperature to normal, but the oscillation of the restored TL peak was much damped. (iii) Cd2+ substitution restored neither of the two EPR signals nor O2 evolution but reversed the abnormal TL peak temperature to normal. However, the reversed TL peak did not show any oscillatory behavior. Given these results, the function of the weakly bound Ca2+ in S-state turnovers in higher plant PSII is discussed.
通过热释光（TL）和低温电子顺磁共振光谱法，对从Ca2+提取、Sr2+取代和Cd2+取代的光系统II（PSII）中形成的S2态的性质进行了比较研究。得到了以下结果：（i）从Ca提取的PSII既没有显示出EPR多线信号，也没有显示出g = 4.1信号，但显示出一个异常的TL带，其峰值温度上移，在用两个或更多闪光激发时不会振荡。向提取的PSII中添加Ca2+可逆转这些效应中的大部分，同时伴随着O2释放的显著恢复，但EPR g = 4.1信号仍然缺失。（ii）Sr2+取代在很大程度上恢复了g = 4.1信号，并部分恢复了多线信号，其形式有所改变，超精细线间距减小，同时伴随着O2释放的部分恢复。Sr2+取代还将异常的TL峰值温度恢复正常，但恢复的TL峰值的振荡大大减弱。（iii）Cd2+取代既没有恢复两个EPR信号中的任何一个，也没有恢复O2释放，但将异常的TL峰值温度恢复正常。然而，反转的TL峰值没有显示出任何振荡行为。基于这些结果，讨论了高等植物PSII中弱结合Ca2+在S态周转中的作用。
