Boussac A, Kuhl H, Un S, Rögner M, Rutherford A W
Section de Bioénergétique, URA CNRS 2096, Gif-sur-Yvette, France.
Biochemistry. 1998 Jun 23;37(25):8995-9000. doi: 10.1021/bi980195b.
The Mn cluster of Photosystem II (PSII) from Synechococcus elongatus was studied using EPR. A signal with features between g = 5 and g = 9 is reported from the S2-state. The signal is attributed to the manganese cluster in a state with a spin 5/2 state. Spectral simulations of the signal indicate zero field splitting parameters where the |E/D| was 0.13. The new signal is formed by irradiating PSII samples which contain the spin = 1/2 S2-state using 813 nm light below 200 K. This effect is attributed to a spin-state change in the manganese cluster due to absorption of the IR light by the Mn-cluster itself. The signal is similar to that reported recently in PSII of plants [Boussac, A., Un, S., Horner, O., and Rutherford, A. W. (1998) Biochemistry 37, 4001-4007]. In plant PSII the comparable signal is formed at a lower temperature (optimally below 77 K), and gradual warming of the sample in the dark leads to the formation of the state responsible for the well-known g = 4.1 signal prior to formation of the spin 1/2 multiline signal. In the present work using cyanobacterial PSII, warming of the sample in the dark leads to the formation of the spin 1/2 multiline signal without formation of the g = 4 type signal as an intermediate. These observations provide a partial explanation for the long-standing "mystery of the missing g = 4 state" in cyanobacterial PSII. The observations are rationalized in terms of three possible states which can exist for S2: (i) the spin 1/2 multiline signal, (ii) the state responsible for the g = 4.1 signal, and (iii) the new spin 5/2 state. The relative stability of these states differs between plants and cyanobacteria.
利用电子顺磁共振（EPR）对聚球藻属细长聚球藻的光系统II（PSII）的锰簇进行了研究。从S2态报告了一个g值在5到9之间的信号。该信号归因于处于自旋5/2态的锰簇。该信号的光谱模拟表明零场分裂参数，其中|E/D|为0.13。通过在200 K以下用813 nm光照射含有自旋= 1/2 S2态的PSII样品形成新信号。这种效应归因于锰簇自身吸收红外光导致锰簇自旋态变化。该信号与最近在植物PSII中报道的信号相似[布萨克，A.，昂，S.，霍纳，O.，和卢瑟福，A. W.（1998年）《生物化学》37，4001 - 4007]。在植物PSII中，可比信号在较低温度（最佳低于77 K）下形成，样品在黑暗中逐渐升温会导致在自旋1/2多线信号形成之前形成负责著名的g = 4.1信号的状态。在目前使用蓝藻PSII的工作中，样品在黑暗中升温会导致自旋1/2多线信号的形成，而不会形成g = 4类型信号作为中间态。这些观察结果为蓝藻PSII中长期存在的“缺失g = 4态之谜”提供了部分解释。这些观察结果根据S2可能存在的三种状态进行了合理化解释：（i）自旋1/2多线信号，（ii）负责g = 4.1信号的状态，以及（iii）新的自旋5/2态。这些状态的相对稳定性在植物和蓝藻之间有所不同。
