González-Pérez Sergio, Quijano Celia, Romero Natalia, Melø Thor Bernt, Radi Rafael, Arellano Juan B
Departamento de Estrés Abiótico, Instituto de Recursos Naturales y Agrobiología de Salamanca (IRNASA-CSIC), Apdo. 257, 37071 Salamanca, Spain.
Arch Biochem Biophys. 2008 May 1;473(1):25-33. doi: 10.1016/j.abb.2008.02.020. Epub 2008 Feb 23.
Peroxynitrite is a strong oxidant that has been proposed to form in chloroplasts. The interaction between peroxynitrite and photosystem II (PSII) has been investigated to determine whether this oxidant could be a hazard for PSII. Peroxynitrite is shown to inhibit oxygen evolution in PSII membranes in a dose-dependent manner. Analyses by PAM fluorimetry and EPR spectroscopy have demonstrated that the inhibition target of peroxynitrite is on the PSII acceptor side. In the presence of the herbicide DCMU, the chlorophyll (Chl) a fluorescence induction curve is inhibited by peroxynitrite, but the slow phase of the Chl a fluorescence decay does not change. EPR studies demonstrate that the Signal II(slow) and Signal II(fast) of peroxynitrite-treated Tris-washed PSII membranes are induced at room temperature, implying that the redox active tyrosines Y(Z) and Y(D) of PSII are not significantly nitrated. A featureless EPR signal with a g value of approximately 2.0043+/-0.0003 and a line width of 10+/-1G is induced under continuous illumination in the presence of peroxynitrite. This new EPR signal corresponds with the semireduced plastoquinone Q(A) in the absence of magnetic interaction with the non-heme Fe2+. We conclude that peroxynitrite impairs PSII electron transport in the Q(A)Fe2+ niche.
过氧亚硝酸盐是一种已被提出会在叶绿体中形成的强氧化剂。人们研究了过氧亚硝酸盐与光系统II（PSII）之间的相互作用，以确定这种氧化剂是否会对PSII构成危害。结果表明，过氧亚硝酸盐会以剂量依赖的方式抑制PSII膜中的氧气释放。通过脉冲幅度调制荧光法（PAM）和电子顺磁共振光谱法（EPR）分析表明，过氧亚硝酸盐的抑制靶点位于PSII受体侧。在除草剂敌草隆（DCMU）存在的情况下，过氧亚硝酸盐会抑制叶绿素（Chl）a荧光诱导曲线，但Chl a荧光衰减的慢相不变。EPR研究表明，经过氧亚硝酸盐处理的Tris洗涤PSII膜的信号II（慢）和信号II（快）在室温下被诱导，这意味着PSII的氧化还原活性酪氨酸Y（Z）和Y（D）没有明显被硝化。在过氧亚硝酸盐存在的情况下，连续光照会诱导出一个g值约为2.0043±0.0003且线宽为10±1G的无特征EPR信号。这个新的EPR信号与在不与非血红素Fe2+发生磁相互作用的情况下半还原的质体醌Q（A）相对应。我们得出结论，过氧亚硝酸盐会损害Q（A）Fe2+区域中的PSII电子传递。
