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首页> 外文期刊>Applied Magnetic Resonance >Pulse ENDOR studies on the radical pair P(700)(+center dot)A(1)(center dot-) and the photoaccumulated quinone acceptor A(1)(center dot-) of photosystem I
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Pulse ENDOR studies on the radical pair P(700)(+center dot)A(1)(center dot-) and the photoaccumulated quinone acceptor A(1)(center dot-) of photosystem I

机译：脉冲ENDOR对光系统I的自由基对P（700）（+中心点）A（1）（中心点-）和光积累的醌受体A（1）（中心点-）的研究

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摘要

The secondary acceptor A(1) of the electron transport chain(s) of photosystem (PS) I is a phylloquinone (vitamin K-1, VK1). Pulse electron paramagnetic resonance and electron nuclear double resonance (ENDOR) experiments at X-band frequencies were performed on the photoaccumulated acceptor radical A(1)(.-) and the radical pair state P(700)(.+)A(1)(.-) in PS I of Thermosynechococcus elongatus. The data obtained were compared with data from the respective radical anion of VK1 in organic solvents. The unusual g tensor magnitude of A(1)(.-) is explained by the hydrophobic binding pocket of this radical. The hyperfine couplings and the spin (and charge) density distribution is very different for A(1)(.-) in PS I and VK1.- in frozen alcoholic solution. This is attributed to a rather strong one-sided hydrogen bond to A(1)(.-). The presence of a hydrogen bond to A(1)(.-) has only a minor effect on g. The hyperfine coupling constants of A(1)(.-) determined from the radical pair spectra deviate only slightly from those derived from photoaccumulated A(1)(.-) in PS I treated with dithionite at high pH. ENDOR resonances of the proton in a H bond were detected and an estimate of the strength and geometry of this bond to A(1)(.-) was obtained. The significance of the hydrogen bond and other (hydrophobic) interactions of A(1) with the surrounding are briefly discussed.
机译：光系统（PS）I的电子传输链的次要受体A（1）是叶醌（维生素K-1，VK1）。在X波段频率上对光累积受体自由基A（1）（.-）和自由基对态P（700）（。+）A（1）进行脉冲电子顺磁共振和电子核双共振（ENDOR）实验（.-）在延长嗜热球菌的PS I中。将获得的数据与来自有机溶剂中VK1的各个自由基阴离子的数据进行比较。 A（1）（.-）的不寻常的g张量值是由该基团的疏水结合口袋解释的。 PS I中的A（1）（.-）和冷冻酒精溶液中的VK1.-的超精细耦合和自旋（和电荷）密度分布非常不同。这归因于与A（1）（.-）相当强的单侧氢键。与A（1）（.-）氢键的存在对g的影响很小。由自由基对光谱确定的A（1）（.-）的超精细偶合常数仅与在高pH下用连二亚硫酸盐处理过的PS I中光积累的A（1）（.-）的那些稍有不同。检测到质子在H键中的ENDOR共振，并获得对该键与A（1）（.-）的键的强度和几何形状的估计。简要讨论了氢键和A（1）与周围的其他（疏水）相互作用的重要性。

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