Department of Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, The Netherlands.
Photosynth Res. 2012 Mar;111(1-2):185-91. doi: 10.1007/s11120-011-9671-z. Epub 2011 Aug 31.
Light energy harvested by the pigments in Photosystem I (PSI) is used for charge separation in the reaction center (RC), after which the positive charge resides on a special chlorophyll dimer called P700. In studies on the PSI trapping kinetics, P700(+) is usually chemically reduced to re-open the RCs. So far, the information available about the reduction rate and possible chlorophyll fluorescence quenching effects of these reducing agents is limited. This information is indispensible to estimate the fraction of open RCs under known experimental conditions. Moreover, it would be important to understand if these reagents have a chlorophyll fluorescence quenching effects to avoid the introduction of exogenous singlet excitation quenching in the measurements. In this study, we investigated the effect of the commonly used reducing agent phenazine methosulfate (PMS) on the RC and fluorescence emission of higher plant PSI-LHCI. We measured the P700(+) reduction rate for different PMS concentrations, and show that we can give a reliable estimation on the fraction of closed RCs based on these rates. The data show that PMS is quenching chlorophyll fluorescence emission. Finally, we determined that the fluorescence quantum yield of PSI with closed RCs is 4% higher than if the RCs are open.
由光合作用系统 I (PSI) 中的色素捕获的光能用于反应中心 (RC) 中的电荷分离，之后正电荷驻留在称为 P700 的特殊叶绿素二聚体上。在 PSI 捕获动力学的研究中，通常通过化学还原 P700(+) 来重新打开 RC。到目前为止，关于这些还原剂的还原速率和可能的叶绿素荧光猝灭效应的信息有限。这些信息对于根据已知实验条件估计开放 RC 的分数是必不可少的。此外，了解这些试剂是否具有叶绿素荧光猝灭效应以避免在测量中引入外源单重态激发猝灭非常重要。在这项研究中，我们研究了常用还原剂吩嗪甲硫酸盐 (PMS) 对高等植物 PSI-LHCI 的 RC 和荧光发射的影响。我们测量了不同 PMS 浓度下的 P700(+)还原速率，并表明我们可以根据这些速率对闭合 RC 的分数进行可靠估计。数据表明 PMS 猝灭叶绿素荧光发射。最后，我们确定闭合 RC 的 PSI 的荧光量子产率比 RC 开放时高 4%。
