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首页> 外文期刊>Biochemistry >No Evidence from FTIR Difference Spectroscopy That Aspartate-170 of the D1 Polypeptide Ligates a Manganese Ion That Undergoes Oxidation during the S(0) to S(1), S(1) to S(2), or S(2) to S(3) Transitions in Photosystem II.
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No Evidence from FTIR Difference Spectroscopy That Aspartate-170 of the D1 Polypeptide Ligates a Manganese Ion That Undergoes Oxidation during the S(0) to S(1), S(1) to S(2), or S(2) to S(3) Transitions in Photosystem II.

机译：从FTIR差异光谱中没有证据表明D1多肽的天冬氨酸170连接了在S（0）到S（1），S（1）到S（2）或S（2）到S期间发生氧化的锰离子（3）Photosystem II中的过渡。

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On the basis of mutagenesis and X-ray crystallographic studies, Asp170 of the D1 polypeptide is widely believed to ligate the (Mn)(4) cluster that is located at the catalytic site of water oxidation in photosystem II. Recent proposals for the mechanism of water oxidation postulate that D1-Asp170 ligates a Mn ion that undergoes oxidation during one or more of the S(0) --> S(1), S(1) --> S(2), and S(2) --> S(3) transitions. To test these hypotheses, we have compared the FTIR difference spectra of the individual S state transitions in wild-type PSII particles from the cyanobacterium Synechocystis sp. PCC 6803 with those in D1-D170H mutant PSII particles. Remarkably, our data show that the D1-D170H mutation does not significantly alter the mid-frequency regions (1800-1000 cm(-)(1)) of any of the FTIR difference spectra. Therefore, we conclude that the oxidation of the (Mn)(4) cluster does not alter the frequencies of the carboxylate stretching modes of D1-Asp170 during the S(0) --> S(1), S(1) --> S(2), or S(2) --> S(3) transitions. The simplest explanation for these data is that the Mn ion that is ligated by D1-Asp170 does not increase its charge or oxidation state during any of these S state transitions. These data have profound implications for the mechanism of water oxidation. Either (1) the oxidation of the Mn ion that is ligated by D1-Asp170 occurs only during the transitory S(3) --> S(4) transition and serves as the critical step in the ultimate formation of the O-O bond or (2) the oxidation increments and O(2) formation chemistry that occur during the catalytic cycle involve only the remaining Mn(3)Ca portion of the Mn(4)Ca cluster. Our data also show that, if the increased positive charge on the (Mn)(4) cluster that is produced during the S(1) --> S(2) transition is delocalized over the (Mn)(4) cluster, it is not delocalized onto the Mn ion that is ligated by D1-Asp170.
机译：在诱变和X射线晶体学研究的基础上，D1多肽的Asp170被广泛认为可以连接位于光系统II中水氧化催化位点的（Mn）（4）簇。关于水氧化机理的最新提议假设D1-Asp170连接一个或多个S（0）-> S（1），S（1）-> S（2）中经历氧化的Mn离子，和S（2）-> S（3）转换。为了检验这些假设，我们比较了来自蓝藻集胞藻属（Synechocystcystis sp）的野生型PSII颗粒中各个S状态跃迁的FTIR差异光谱。 PCC 6803与D1-D170H突变PSII颗粒中的那些。值得注意的是，我们的数据显示D1-D170H突变不会显着改变任何FTIR差异谱的中频区域（1800-1000 cm（-）（1））。因此，我们得出结论，在（S）（0）-> S（1），S（1）-期间，（Mn）（4）簇的氧化不会改变D1-Asp170的羧酸盐拉伸模式的频率。 > S（2）或S（2）-> S（3）转换。这些数据的最简单解释是，在任何这些S状态跃迁期间，被D1-Asp170连接的Mn离子不会增加其电荷或氧化态。这些数据对水氧化机理具有深远的意义。 （1）由D1-Asp170连接的Mn离子的氧化仅在瞬时S（3）-> S（4）过渡期间发生，并且是OO键最终形成的关键步骤或（ 2）在催化循环过程中发生的氧化增量和O（2）形成化学仅涉及Mn（4）Ca簇的其余Mn（3）Ca部分。我们的数据还显示，如果在S（1）-> S（2）过渡过程中产生的（Mn）（4）簇上增加的正电荷在（Mn）（4）簇上离域，则它D 1 -Asp 170连接的Mn离子上没有被离域。

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