I(2)BC, UMR CNRS 9198, CEA Saclay, 91191 Gif-sur-Yvette, France.
Proteo-Science Research Center, Department of Chemistry, Graduate School of Science and Technology, Ehime University, Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan.
Biochim Biophys Acta Bioenerg. 2022 Jun 1;1863(5):148546. doi: 10.1016/j.bbabio.2022.148546. Epub 2022 Mar 23.
The stoichiometry and kinetics of the proton release were investigated during each transition of the S-state cycle in Photosystem II (PSII) from Thermosynechococcus elongatus containing either a MnCaO (PSII/Ca) or a MnSrO (PSII/Sr) cluster. The measurements were done at pH 6.0 and pH 7.0 knowing that, in PSII/Ca at pH 6.0 and pH 7.0 and in PSII/Sr at pH 6.0, the flash-induced S-state is in a low-spin configuration (S) whereas in PSII/Sr at pH 7.0, the S-state is in a high-spin configuration (S) in half of the centers. Two measurements were done; the time-resolved flash dependent i) absorption of either bromocresol purple at pH 6.0 or neutral red at pH 7.0 and ii) electrochromism in the Soret band of P at 440 nm. The fittings of the oscillations with a period of four indicate that one proton is released in the S to S transition in PSII/Sr at pH 7.0. It has previously been suggested that the proton released in the S to S transition would be released in a STyr → STyr transition before the electron transfer from the cluster to Tyr occurs. The release of a proton in the STyr → STyr transition would logically imply that this proton release is missing in the STyr to STyr transition. Instead, the proton release in the S to S transition in PSII/Sr at pH 7.0 was mainly done at the expense of the proton release in the S to S and S to S transitions. However, at pH 7.0, the electrochromism of P seems larger in PSII/Sr when compared to PSII/Ca in the S state. This points to the complex link between proton movements in and immediately around the Mn cluster and the mechanism leading to the release of protons into the bulk.
在来自 Thermosynechococcus elongatus 的含有 MnCaO（PSII/Ca）或 MnSrO（PSII/Sr）簇的 PSII 中，研究了 S 态循环的每个转变过程中质子释放的化学计量和动力学。在 pH 6.0 和 pH 7.0 下进行了测量，因为在 PSII/Ca 下在 pH 6.0 和 pH 7.0 下和在 PSII/Sr 下在 pH 6.0 下，闪光诱导的 S 态处于低自旋构象（S），而在 PSII/Sr 下在 pH 7.0 下，一半中心的 S 态处于高自旋构象（S）。进行了两项测量；时间分辨闪光依赖性 i）在 pH 6.0 下用溴甲酚紫或在 pH 7.0 下用中性红吸收 ii）在 440nm 处 P 的 Soret 带中的电色性。用周期为四的振荡拟合表明，在 pH 7.0 下的 PSII/Sr 中的 S 到 S 转变中释放了一个质子。先前已经提出，在电子从簇转移到 Tyr 之前，在 S 到 S 转变中释放的质子将在 STyr→STyr 转变中释放。在 STyr→STyr 转变中释放质子将合乎逻辑地意味着在 STyr 到 STyr 转变中缺少这种质子释放。相反，在 pH 7.0 下的 PSII/Sr 中的 S 到 S 转变中的质子释放主要是通过 S 到 S 和 S 到 S 转变中的质子释放来完成的。然而，在 pH 7.0 下，与 PSII/Ca 相比，PSII/Sr 中的 P 的电色性似乎更大。这表明 Mn 簇内和周围质子运动与导致质子释放到体相的机制之间存在复杂的联系。
