The Mn4 CaO5 cluster of Photosystem II (PSII) advances sequentially through five oxidation states (S0 to S4 ). Under the enzyme cycle, two water molecules are oxidized, O2 is generated and four protons are released into the lumen. Umena et al. (2011) have proposed that, with other charged amino acids, the R323 residue of the D1 protein could contribute to regulate a proton egress pathway from the Mn4 CaO5 cluster and TyrZ via a proton channel identified from the 3D structure. To test this suggestion, a PsbA3/R323E site-directed mutant has been constructed and the properties of its PSII have been compared to those of the PsbA3-PSII by using EPR spectroscopy, polarography, thermoluminescence and time-resolved UV-visible absorption spectroscopy. Neither the oscillations with a period four nor the kinetics and S-state-dependent stoichiometry of the proton release were affected. However, several differences have been found: i) the P680 + decay in the hundreds of ns time domain was much slower in the mutant, ii) the S2 QA - /DCMU and S3 QA - /DCMU radiative charge recombination occurred at higher temperatures and iii) the S0 TyrZ • , S1 TyrZ • , S2 TyrZ • split EPR signals induced at 4.2 K by visible light from the S0 TyrZ , S1 TyrZ , S2 TyrZ , respectively, and the (S2 TyrZ • )' induced by NIR illumination at 4.2 K of the S3 TyrZ state differed. It is proposed that the R323 residue of the D1 protein interacts with TyrZ likely via the H-bond network previously proposed to be a proton channel. Therefore, rather than participating in the egress of protons to the lumen, this channel could be involved in the relaxations of the H-bonds around TyrZ by interacting with the bulk, thus tuning the driving force required for TyrZ oxidation. This article is protected by copyright. All rights reserved.

中文翻译：

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探讨 D1 蛋白精氨酸 323 在光系统 II 功能中的作用‡

光系统 II (PSII) 的 Mn4 CaO5 簇依次通过五个氧化态（S0 到 S4）前进。在酶循环下，两个水分子被氧化，产生O2，四个质子释放到管腔中。乌梅纳等人。(2011) 提出，与其他带电氨基酸一起，D1 蛋白的 R323 残基可能有助于通过从 3D 结构识别的质子通道调节来自 Mn4 CaO5 簇和 TyrZ 的质子流出途径。为了验证这一建议，我们构建了 PsbA3/R323E 定点突变体，并通过使用 EPR 光谱、极谱、热释光和时间分辨紫外-可见吸收光谱将其 PSII 的特性与 PsbA3-PSII 的特性进行了比较。周期为 4 的振荡和质子释放的动力学和 S 态相关的化学计量都不受影响。然而，已经发现了一些差异：i) 突变体中数百 ns 时域中的 P680 + 衰减要慢得多，ii) S2 QA - /DCMU 和 S3 QA - /DCMU 辐射电荷复合发生在更高的温度和iii) S0 TyrZ • 、S1 TyrZ • 、S2 TyrZ • 分别由来自 S0 TyrZ 、S1 TyrZ 、S2 TyrZ 的可见光在 4.2 K 诱导的 EPR 信号和由 NIR 照明诱导的 (S2 TyrZ • )' 分离S3 TyrZ 状态的 4.2 K 不同。提出 D1 蛋白的 R323 残基与 TyrZ 相互作用，可能是通过先前被认为是质子通道的 H 键网络。因此，与其参与质子向管腔的出口，该通道可能通过与主体相互作用参与 TyrZ 周围 H 键的松弛，从而调整 TyrZ 氧化所需的驱动力。本文受版权保护。版权所有。