Parallel polarization EPR detection of an S1-state "multiline" EPR signal in photosystem II particles from Synechocystis sp. PCC 6803
Parallel polarization EPR detection of an S1-state "multiline" EPR signal in photosystem II particles from Synechocystis sp. PCC 6803
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DOI：
10.1021/ja972693y
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发表时间：
1998-01-21
影响因子：
15
通讯作者：
Britt, RD
中科院分区：
文献类型：
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作者：
Campbell, KA;Peloquin, JM;Britt, RD
光系统II（PS II）氧释放通过五个“S-状态”中间体S 0至S4的循环发生，其中下标表示通过光氧化的P680+ Chl部分从PS II氧释放复合物（OEC）提取的氧化当量的数目。1，2 OEC由一个四核Mn簇，氧化还原活性酪氨酸YZ，和必要的辅因子Cl-和Ca 2+。2.奇电子S2态的广泛EPR表征导致了我们目前对Mn簇的结构、蛋白质连接、底物和抑制剂结合模式的许多了解。2，3然而，EPR表征的OEC的更减少的S 0-和S1-状态仍然更加难以捉摸。考虑到S2态的奇自旋磁性，S1态必须有偶数个电子分配在OEC的四个Mn离子中。如果这些电子分布在单个交换耦合四核簇的离子之间，例如对于奇电子S2-态，3d-g所观察到的，则可以预期整数自旋态的能量阶梯，包括抗磁性S 0 0态。耦合簇的基态和激发态的有效自旋值将覆盖0和最大值Smax之间的范围，这取决于S1态配置中存在的各个Mn氧化态。[4]根据温度和耦合团簇阶梯内能隙的大小，这些激发态中的一些可能加入基态，对团簇的磁性做出贡献。或者，S1态可以由较低阶的磁性单元组成，例如一对非相互作用的双核簇，一个三核簇与一个非相互作用的单体，一个双核簇与一对非相互作用的单体，甚至四个非相互作用的单体。对于具有不可忽略的零场分裂相互作用的整数自旋系统，在振荡磁场BB 1与静磁场BB 0平行的条件下进行EPR实验，可以灵敏地探测到“Δ（MS）0”电子自旋跃迁. 5 Dexheimer和Klein 6将这种平行极化EPR光谱应用于富含PS II的菠菜类囊体膜中OEC的研究，并报告了一个宽（600 G峰-峰宽度），无特征的EPR信号集中在光谱的g）4.8区域，他们将其指定为S1-状态中存在的S）1自旋状态。这个光谱
Photosystem II (PS II) oxygen evolution occurs through a cycle of five “S-state” intermediates, S0 through S4, where the subscript represents the number of oxidizing equivalents abstracted from the PS II oxygen eVolVing complex (OEC) by the photooxidized P680+ Chl moiety. 1, 2 The OEC consists of a tetranuclear Mn cluster, the redox-active tyrosine YZ, and the essential cofactors Cl-and Ca2+. 2 Extensive EPR characterization of the odd-electron S2 state has led to much of our current knowledge of the structure, protein ligation, and substrate and inhibitor binding modes of the Mn cluster. 2, 3 However, EPR characterization of the more reduced S0-and S1-states of the OEC has remained more elusive. Given the odd-spin magnetic properties of the S2-state, the S1-state must have an even number of electrons partitioned among the four Mn ions of the OEC. If these electrons are distributed among the ions of a single exchange-coupled tetranuclear cluster, such as observed for the odd-electron S2-state, 3d-g one would expect an energy ladder of integer spins states, including the diamagnetic S) 0 state. The effective spin values of the ground and excited states of the coupled cluster will cover the range between 0 and a maximum value, Smax, which depends on the individual Mn oxidation states present in the S1-state configuration. 4 Depending on the temperature and the magnitudes of the energy gaps within the ladder of the coupled cluster, some of these excited states may join the ground state in contributing to the magnetic properties of the cluster. Alternatively, the S1-state could consist of lower order magnetic units, such as a pair of noninteracting dinuclear clusters, a trinuclear cluster with a noninteracting monomer, a dinuclear cluster with a pair of noninteracting monomers, or even four noninteracting monomers. Thus, characterization of the magnetic properties of the S1-state is important for our understanding of the structure of the OEC.For integer spin systems with nonnegligible zero-field splitting interactions, the EPR experiment, performed with the oscillating magnetic field BB1 polarized parallel to the static magnetic field BB0, can provide for sensitive detection of “ΔMS) 0” electron spin transitions. 5 Dexheimer and Klein6 applied such parallel polarization EPR spectroscopy to the study of the OEC in PS II-enriched spinach thylakoid membranes and reported a broad (600 G peak-to-peak width), featureless EPR signal centered about the g) 4.8 region of the spectrum, which they assigned to an S) 1 spin state present in the S1-state. This spectrum bears