Data on the manganese cluster's oxidation state via photoactivation of photosystem II microcrystals

Knowledge of the manganese oxidation states of the oxygen-evolving Mn4CaO5 cluster in photosystem II (PSII) is crucial toward understanding the mechanism of biological water oxidation. There is a 4 decade long debate on this topic that historically originates from the observation of a multiline electron paramagnetic resonance (EPR) signal with effective total spin of S = 1/2 in the singly oxidized S2 state of this cluster. This signal implies an overall oxidation state of either Mn(III)3Mn(IV) or Mn(III)Mn(IV)3 for the S2 state. These 2 competing assignments are commonly known as "low oxidation (LO)" and "high oxidation (HO)" models of the Mn4CaO5 cluster. Recent advanced EPR and Mn K-edge X-ray spectroscopy studies converge upon the HO model. However, doubts about these assignments have been voiced, fueled especially by studies counting the number of flash-driven electron removals required for the assembly of an active Mn4CaO5 cluster starting from Mn(II) and Mn-free PSII. This process, known as photoactivation, appeared to support the LO model since the first oxygen is reported to evolve already after 7 flashes. In this study, we improved the quantum yield and sensitivity of the photoactivation experiment by employing PSII microcrystals that retained all protein subunits after complete manganese removal and by oxygen detection via a custom built thin-layer cell connected to a membrane inlet mass spectrometer. We demonstrate that 9 flashes by a nanosecond laser are required for the production of the first oxygen, which proves that the HO model provides the correct description of the Mn4CaO5 cluster's oxidation states.

The dataset was originally published in DiVA and moved to SND in 2024.

了解光系统II（PSII）中放氧Mn4CaO5簇的锰氧化态，对于理解生物水氧化机制至关重要。这一主题的争论已持续40年，其历史根源在于观察到该簇单氧化S2态中存在有效总自旋S=1/2的多线电子顺磁共振（EPR）信号。该信号表明S2态的整体氧化态要么是Mn(III)₃Mn(IV)，要么是Mn(III)Mn(IV)₃。这两种相互竞争的赋值通常被称为Mn4CaO5簇的‘低氧化（LO）’和‘高氧化（HO）’模型。近期先进的EPR和锰K边X射线光谱学研究一致支持HO模型。然而，对这些赋值的质疑依然存在，尤其是源于从Mn(II)和无锰PSII组装活性Mn4CaO5簇所需的闪光驱动电子移除数量的研究。这一被称为光激活的过程似乎支持LO模型，因为据报道首次放氧在7次闪光后就已发生。在本研究中，我们通过使用完全去除锰后仍保留所有蛋白质亚基的PSII微晶，并通过连接到膜进样质谱仪的定制薄层池进行氧检测，提高了光激活实验的量子产率和灵敏度。我们证明，纳秒激光的9次闪光是产生首次氧所必需的，这表明HO模型对Mn4CaO5簇的氧化态提供了正确描述。该数据集最初发表于DiVA，并于2024年迁移至SND。