Stevens Gregory B, Lukins Philip B
CSIRO Telecommunications and Industrial Physics, Bradfield Road, Lindfield, NSW 2070, Australia.
Biochim Biophys Acta. 2003 Aug 18;1605(1-3):21-34. doi: 10.1016/s0005-2728(03)00061-6.
We report for the first time significant changes in the P680*+ reduction kinetics of Photosystem II (PS II) in which the 17 and 23 kDa extrinsic polypeptides are intact, in the presence of Ca(2+) or ethylene glycol bis (beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) which were added to vary the Ca(2+) concentration from 5 microM to 30 mM. The decrease in the extent of normal P680*+ reduction decay with lifetimes of 40-370 ns and a corresponding increase in the extent of kinetics with lifetimes of 20-220 micros was interpreted as being due to electron transfer from Y(Z) to P680*+ being replaced by slow forward conduction and by processes including P680*+/Q(A)(-) recombination. The question of whether changes in P680*+ reduction kinetics were caused by loss of Ca(2+) from PS II or by direct interaction of EGTA with PS II was addressed by lowering the free-Ca(2+) concentration of suspensions of PS II core complexes by serial dilution in the absence of EGTA. Despite a significant decrease in the rate of O(2) evolution after this treatment, only small changes in the P680*+ reduction kinetics were observed. Loss of Ca(2+) did not affect P680*+ reduction associated with electron transfer from Y(Z). Since much larger changes in the P680*+ reduction kinetics of intact PS II occurred at comparable free-Ca(2+) concentrations in the presence of EGTA, we conclude that EGTA influenced the P680*+ reduction kinetics by directly interacting with PS II rather than by lowering the free Ca(2+) concentration of the surrounding media. Notwithstanding these effects, we show that useful information about Ca(2+) binding to PS II can be obtained when direct interaction of EGTA is taken into account.
我们首次报道了在光系统II（PS II）中，17 kDa和23 kDa外在多肽保持完整的情况下，添加Ca(2+)或乙二醇双（β-氨基乙醚）-N,N,N',N'-四乙酸（EGTA）以将Ca(2+)浓度从5 microM变化至30 mM时，P680*+还原动力学的显著变化。正常P680*+还原衰减程度的降低，其寿命为40 - 370 ns，以及相应的寿命为20 - 220微秒的动力学程度的增加，被解释为是由于从Y(Z)到P680*+的电子转移被缓慢的正向传导以及包括P680*+/Q(A)(-)重组的过程所取代。通过在不存在EGTA的情况下进行系列稀释来降低PS II核心复合物悬浮液的游离Ca(2+)浓度，解决了P680*+还原动力学变化是由PS II中Ca(2+)的损失还是EGTA与PS II的直接相互作用引起的问题。尽管此处理后O(2)释放速率显著降低，但仅观察到P680*+还原动力学的微小变化。Ca(2+)的损失不影响与从Y(Z)进行电子转移相关的P680*+还原。由于在存在EGTA的情况下，完整PS II的P680*+还原动力学在相当的游离Ca(2+)浓度下发生了大得多的变化，我们得出结论，EGTA通过直接与PS II相互作用而非通过降低周围介质的游离Ca(2+)浓度来影响P680*+还原动力学。尽管有这些影响，但我们表明，当考虑EGTA的直接相互作用时，可以获得有关Ca(2+)与PS II结合的有用信息。
