Vass I, Sass L, Spetea C, Bakou A, Ghanotakis D F, Petrouleas V
Institute of Plant Biology, Biological Research Center, Szeged, Hungary.
Biochemistry. 1996 Jul 9;35(27):8964-73. doi: 10.1021/bi9530595.
Inhibition of photosystem II electron transport by UV-B radiation has been studied in isolated spinach photosystem II membrane particles using low-temperature EPR spectroscopy and chlorophyll fluorescence measurements. UV-B irradiation results in the rapid inhibition of oxygen evolution and the decline of variable chlorophyll fluorescence. These effects are accompanied by the loss of the multiline EPR signal arising from the S2 state of the water-oxidizing complex and the induction of Signal IIfast originating from stabilized Try-Z+. The EPR signals from the QA-Fe2+ acceptor complex, Tyr-D+, and the oxidized non-heme iron (Fe3+) are also decreased during the course of UV-B irradiation, but at a significantly slower rate than oxygen evolution and the multiline signal. The decrease of the Fe3+ signal at high g values (g = 8.06, g = 5.6) is accompanied by the induction of another EPR signal at g = 4.26 that arises most likely from the same Fe3+ ion in a modified ligand environment. UV-B irradiation also affects cytochrome b-559. The g = 2.94 EPR signal that arises from the dark- oxidized form is enhanced, whereas the light inducible g = 3.04 signal that arises from the photo-oxidizable population of cytochrome b-559 is diminished. UV-B irradiation also induces the degradation of the D1 reaction center protein. The rate of the D1 protein loss is slower than the inhibition of oxygen evolution and of the multiline signal but follows closely the loss of Signal IIslow, the QA-Fe2+ and the Fe3+ EPR signals, as well as the release of protein-bound manganese. It is concluded from the results that UV-B radiation affects photosystem II redox components at both the donor and acceptor side. The primary damage occurs at the water-oxidizing complex. Modification and/or inactivation of tyrosine-D, cytochrome b-559, and the QAFe2+ acceptor complex are subsequent events that coincide more closely with the UV-B-induced damage to the protein structure of the photosystem II reaction center.
利用低温电子顺磁共振光谱和叶绿素荧光测量技术，在分离的菠菜光系统II膜颗粒中研究了UV - B辐射对光系统II电子传递的抑制作用。UV - B照射导致氧气释放迅速受到抑制，可变叶绿素荧光下降。这些效应伴随着水氧化复合物S2态产生的多线电子顺磁共振信号的丧失以及源自稳定化的Try - Z + 的快速信号II的诱导。在UV - B照射过程中，来自QA - Fe2 + 受体复合物、Tyr - D + 和氧化的非血红素铁（Fe3 + ）的电子顺磁共振信号也会降低，但速率明显慢于氧气释放和多线信号。高g值（g = 8.06，g = 5.6）处Fe3 + 信号的降低伴随着g = 4.26处另一个电子顺磁共振信号的诱导，该信号很可能来自处于修饰配体环境中的同一Fe3 + 离子。UV - B照射还会影响细胞色素b - 559。由暗氧化形式产生的g = 2.94电子顺磁共振信号增强，而由细胞色素b - 559的可光氧化群体产生的光诱导g = 3.04信号减弱。UV - B照射还会诱导D1反应中心蛋白的降解。D1蛋白损失的速率比氧气释放和多线信号的抑制速率慢，但与缓慢信号II、QA - Fe2 + 和Fe3 + 电子顺磁共振信号的损失以及蛋白质结合锰的释放密切相关。从结果可以得出结论，UV - B辐射影响光系统II供体侧和受体侧的氧化还原成分。主要损伤发生在水氧化复合物处。酪氨酸 - D、细胞色素b - 559和QAFe2 + 受体复合物的修饰和/或失活是后续事件，与UV - B诱导的光系统II反应中心蛋白质结构损伤更密切相关。
