Jansson Hanna, Hansson Orjan
Department of Chemistry, University of Gothenburg, PO Box 462, SE-405 30 Gothenburg, Sweden.
Biochim Biophys Acta. 2008 Sep;1777(9):1116-21. doi: 10.1016/j.bbabio.2008.03.032. Epub 2008 Apr 10.
The electron transfer from wild-type spinach plastocyanin (Pc) to photosystem 1 has been studied by flash-induced absorption changes at 830 nm. The decay kinetics of photo-oxidized P700 are drastically slower in the presence of Ag(I)-substituted Pc, while addition of Zn(II)-substituted Pc has a weaker effect. The metal-substituted forms of Pc act as competitive inhibitors of the reaction between normal, Cu-containing, Pc and P700. The inhibition constants obtained from an analysis of the kinetic data were 30 and 410 microM for Ag(I)- and Zn(II)-substituted Pc, respectively. When the Gly8Asp mutant form of Pc was used instead of the wild-type form, the corresponding values were found to be 77 and 442 microM. If the Ag- and Zn-derivatives can be considered as structural mimics of reduced and oxidized CuPc, respectively, our results imply that there is a redox-induced decrease in the affinity between Pc and photosystem 1 that follows the electron donation to P700. Our data also imply that the Gly8Asp mutation can diminish the magnitude of this change. The findings reported here are consistent with a reaction mechanism where the electron transfer in the complex between Pc and photosystem 1 is assumed to be reversible.
通过830nm处的闪光诱导吸收变化，研究了野生型菠菜质体蓝素（Pc）向光系统1的电子转移。在存在Ag（I）取代的Pc时，光氧化的P700的衰减动力学显著减慢，而添加Zn（II）取代的Pc的影响较弱。Pc的金属取代形式作为正常含铜Pc与P700之间反应的竞争性抑制剂。根据动力学数据分析得到的Ag（I）和Zn（II）取代的Pc的抑制常数分别为30和410μM。当使用Pc的Gly8Asp突变体形式代替野生型形式时，相应的值分别为77和442μM。如果Ag和Zn衍生物可分别视为还原态和氧化态CuPc的结构模拟物，我们的结果表明，在向P700供电子后，Pc与光系统1之间的亲和力会因氧化还原作用而降低。我们的数据还表明，Gly8Asp突变可以减小这种变化的幅度。此处报道的结果与一种反应机制一致，即假定Pc与光系统1之间复合物中的电子转移是可逆的。
