I(2)BC, CNRS UMR 9198, CEA Saclay, 91191 Gif-sur-Yvette, France.
Institut de Biologie Physico-Chimique, CNRS UMR 7141 and Sorbonne Université, 13 rue Pierre et Marie Curie, 75005 Paris, France.
Biochim Biophys Acta Bioenerg. 2020 Jun 1;1861(5-6):148176. doi: 10.1016/j.bbabio.2020.148176. Epub 2020 Feb 19.
Electrochromic band-shifts have been investigated in Photosystem II (PSII) from Thermosynechoccocus elongatus. Firstly, by using Mn-depleted PsbA1-PSII and PsbA3-PSII in which the Q absorption of Phe differs, a band-shift in the Q region of Phe centered at ~ 544 nm has been identified upon the oxidation, at pH 8.6, of Tyr. In contrast, a band-shift due to the formation of either Q or Tyr is observed in PsbA3-PSII at ~ 546 nm, as expected with E130 H-bonded to Phe and at ~ 544 nm as expected with Q130 H-bonded to Phe. Secondly, electrochromic band-shifts in the Chla Soret region have been measured in O-evolving PSII in PsbA3-PSII, in the PsbA3/H198Q mutant in which the Soret band of P is blue shifted and in the PsbA3/T179H mutant. Upon TyrQ formation the Soret band of P is red shifted and the Soret band of Chl is blue shifted. In contrast, only P undergoes a detectable S-state dependent electrochromism. Thirdly, the time resolved S-state dependent electrochromism attributed to P is biphasic for all the S-state transitions except for S to S, and shows that: i) the proton release in S to S occurs after the electron transfer and ii) the proton release and the electron transfer kinetics in S to S, in T. elongatus, are significantly faster than often considered. The nature of STyr is discussed in view of the models in the literature involving intermediate states in the S to S transition.
电致变色带位移已在 Thermosynechoccocus elongatus 的光系统 II (PSII) 中进行了研究。首先，通过使用 Mn 耗尽的 PsbA1-PSII 和 PsbA3-PSII，其中 Phe 的 Q 吸收不同，在 pH 8.6 下氧化 Tyr 时，在 Phe 的 Q 区域中心观察到约 544nm 的带位移。相比之下，在 PsbA3-PSII 中，由于 Q 或 Tyr 的形成而观察到的带位移位于约 546nm，这与 E130 与 Phe 形成氢键时的预期一致，并且在约 544nm 时与 Q130 与 Phe 形成氢键时的预期一致。其次，在 PsbA3-PSII 中的 O 释放 PSII 中测量了 Chla Soret 区域中的电致变色带位移，在 PsbA3/H198Q 突变体中 P 的 Soret 带蓝移，在 PsbA3/T179H 突变体中 P 的 Soret 带蓝移。在 TyrQ 形成时，P 的 Soret 带红移，Chl 的 Soret 带蓝移。相比之下，只有 P 发生可检测到的 S 态依赖的电致变色。第三，归因于 P 的时间分辨 S 态依赖的电致变色在所有 S 态跃迁中除 S 到 S 之外均为两相，表明：i）在电子转移后发生 S 到 S 的质子释放，ii）在 T.elongatus 中，S 到 S 的质子释放和电子转移动力学明显快于通常认为的。根据文献中涉及 S 到 S 跃迁中间态的模型，讨论了 STyr 的性质。
