Department of Biophysics, Centre of the Region Haná for Biotechnological and Agricultural Research, Faculty of Science, Palacký University, Olomouc, Czech Republic.
PLoS One. 2012;7(9):e45883. doi: 10.1371/journal.pone.0045883. Epub 2012 Sep 26.
When photosystem II (PSII) is exposed to excess light, singlet oxygen ((1)O(2)) formed by the interaction of molecular oxygen with triplet chlorophyll. Triplet chlorophyll is formed by the charge recombination of triplet radical pair (3)[P680(•+)Pheo(•-)] in the acceptor-side photoinhibition of PSII. Here, we provide evidence on the formation of (1)O(2) in the donor side photoinhibition of PSII. Light-induced (1)O(2) production in Tris-treated PSII membranes was studied by electron paramagnetic resonance (EPR) spin-trapping spectroscopy, as monitored by TEMPONE EPR signal. Light-induced formation of carbon-centered radicals (R(•)) was observed by POBN-R adduct EPR signal. Increased oxidation of organic molecules at high pH enhanced the formation of TEMPONE and POBN-R adduct EPR signals in Tris-treated PSII membranes. Interestingly, the scavenging of R(•) by propyl gallate significantly suppressed (1)O(2). Based on our results, it is concluded that (1)O(2) formation correlates with R(•) formation on the donor side of PSII due to oxidation of organic molecules (lipids and proteins) by long-lived P680(•+)/TyrZ(•). It is proposed here that the Russell mechanism for the recombination of two peroxyl radicals formed by the interaction of R(•) with molecular oxygen is a plausible mechanism for (1)O(2) formation in the donor side photoinhibition of PSII.
当光系统 II（PSII）暴露在过量光下时，分子氧与三重态叶绿素相互作用形成单线态氧（(1)O(2)）。三重态叶绿素是由 PSII 受体侧光抑制中三重态自由基对（3）[P680(•+)Pheo(•-)]的电荷复合形成的。在这里，我们提供了 PSII 供体侧光抑制中（1）O(2)形成的证据。通过电子顺磁共振（EPR）自旋捕获光谱研究了 Tris 处理的 PSII 膜中光诱导的（1）O(2)产生，通过 TEMPONE EPR 信号进行监测。通过 POBN-R 加合物 EPR 信号观察到光诱导的碳中心自由基（R(•)）的形成。在高 pH 值下，氧化有机分子的增加增强了 Tris 处理的 PSII 膜中 TEMPONE 和 POBN-R 加合物 EPR 信号的形成。有趣的是，丙基 gallate 对 R(•)的清除显著抑制了（1）O(2)。根据我们的结果，得出结论，由于有机分子（脂质和蛋白质）被长寿命 P680(•+)/TyrZ(•)氧化，（1）O(2)的形成与 PSII 供体侧的 R(•)形成相关。这里提出的是，通过 R(•)与分子氧相互作用形成的两个过氧自由基的 Russell 机制是 PSII 供体侧光抑制中（1）O(2)形成的合理机制。
