Ho Felix M, Morvaridi Susan F, Mamedov Fikret, Styring Stenbjörn
Molecular Biomimetics, Department of Photochemistry and Molecular Science, Angström Laboratory, Uppsala University, Uppsala, Sweden.
Biochim Biophys Acta. 2007 Jan;1767(1):5-14. doi: 10.1016/j.bbabio.2006.08.006. Epub 2006 Aug 22.
The long-lived, light-induced radical Y(D) of the Tyr161 residue in the D2 protein of Photosystem II (PSII) is known to magnetically interact with the CaMn(4) cluster, situated approximately 30 A away. In this study we report a transient step-change increase in Y(D) EPR intensity upon the application of a single laser flash to S(1) state-synchronised PSII-enriched membranes from spinach. This transient effect was observed at room temperature and high applied microwave power (100 mW) in samples containing PpBQ, as well as those containing DCMU. The subsequent decay lifetimes were found to differ depending on the additive used. We propose that this flash-induced signal increase was caused by enhanced spin relaxation of Y(D) by the OEC in the S(2) state, as a consequence of the single laser flash turnover. The post-flash decay reflected S(2)-->S(1) back-turnover, as confirmed by their correlations with independent measurements of S(2) multiline EPR signal and flash-induced variable fluorescence decay kinetics under corresponding experimental conditions. This flash-induced effect opens up the possibility to study the kinetic behaviour of S-state transitions at room temperature using Y(D) as a probe.
已知光系统II（PSII）的D2蛋白中Tyr161残基的长寿命光诱导自由基Y（D）与距离约30埃的CaMn(4)簇发生磁相互作用。在本研究中，我们报告了对来自菠菜的S(1)态同步的富含PSII的膜施加单个激光闪光后，Y（D）电子顺磁共振（EPR）强度出现瞬态阶跃增加。在室温以及含有2,5-二溴-3-甲基-6-异丙基对苯二酚（PpBQ）或敌草隆（DCMU）的样品中，在高微波功率（100毫瓦）下观察到了这种瞬态效应。发现随后的衰减寿命因所使用的添加剂而异。我们提出，这种闪光诱导的信号增加是由于在单个激光闪光周转后，S(2)态的放氧复合体（OEC）增强了Y（D）的自旋弛豫所致。闪光后的衰减反映了S(2)-->S(1)的反向周转，这在相应实验条件下通过它们与S(2)多线EPR信号的独立测量以及闪光诱导的可变荧光衰减动力学的相关性得到了证实。这种闪光诱导效应为利用Y（D）作为探针在室温下研究S态转变的动力学行为开辟了可能性。
