Photosystem II (PSII) is an intrinsic membrane protein complex that functions as a light-driven water:plastoquinone oxidoreductase in oxygenic photosynthesis. Electron transport in PSII is associated with formation of reactive oxygen species (ROS) responsible for oxidative modifications of PSII proteins. In this study, oxidative modifications of the D1 and D2 proteins by the superoxide anion (O₂^•−) and the hydroxyl (HO^•) radicals were studied in WT and a tocopherol cyclase (vte1) mutant, which is deficient in the lipid-soluble antioxidant α-tocopherol. In the absence of this antioxidant, high-resolution tandem mass spectrometry was used to identify oxidation of D1:¹³⁰E to hydroxyglutamic acid by O₂^•− at the Pheo_D1 site. Additionally, D1:²⁴⁶Y was modified to either tyrosine hydroperoxide or dihydroxyphenylalanine by O₂^•− and HO^•, respectively, in the vicinity of the nonheme iron. We propose that α-tocopherol is localized near Pheo_D1 and the nonheme iron, with its chromanol head exposed to the lipid–water interface. This helps to prevent oxidative modification of the amino acid’s hydrogen that is bonded to Pheo_D1 and the nonheme iron (via bicarbonate), and thus protects electron transport in PSII from ROS damage.

光系统 II (PSII) 是一种内在的膜蛋白复合物，在有氧光合作用中起光驱动水：质体醌氧化还原酶的作用。PSII 中的电子传输与负责 PSII 蛋白氧化修饰的活性氧 (ROS) 的形成有关。在这项研究中_，在WT和缺乏^脂质-可溶性抗氧化剂α-生育酚。在没有这种抗氧化剂的情况下，使用高分辨率串联质谱法鉴定 D1：^{130 E 被 O} ₂氧化为羟基谷氨酸^•−在Pheo _D1站点。此外，在非血红素铁附近，D1: ²⁴⁶ Y 分别被 O ₂ ^•-和 HO ^{•修饰为酪氨酸过氧化氢或二羟基苯丙氨酸。}我们建议 α-生育酚位于 Pheo _D1和非血红素铁附近，其色原醇头暴露于脂质-水界面。_{这有助于防止与 Pheo D1}和非血红素铁（通过碳酸氢盐）键合的氨基酸氢发生氧化修饰，从而保护 PSII 中的电子传输免受 ROS 损伤。