Haumann M, Liebisch P, Müller C, Barra M, Grabolle M, Dau H
Freie Universität Berlin, FB Physik, Arnimallee 14, D-14195 Berlin, Germany.
Science. 2005 Nov 11;310(5750):1019-21. doi: 10.1126/science.1117551.
Plants and cyanobacteria produce atmospheric dioxygen from water, powered by sunlight and catalyzed by a manganese complex in photosystem II. A classic S-cycle model for oxygen evolution involves five states, but only four have been identified. The missing S4 state is particularly important because it is directly involved in dioxygen formation. Now progress comes from an x-ray technique that can monitor redox and structural changes in metal centers in real time with 10-microsecond resolution. We show that in the O2-formation step, an intermediate is formed--the enigmatic S4 state. Its creation is identified with a deprotonation process rather than the expected electron-transfer mechanism. Subsequent electron transfer would give an additional S4' state, thus extending the fundamental S-state cycle of dioxygen formation.
植物和蓝细菌利用阳光提供能量，并在光系统II中由锰复合物催化，从水中产生大气中的氧气。一个经典的氧气释放S循环模型涉及五个状态，但目前仅识别出其中四个。缺失的S4状态尤为重要，因为它直接参与了氧气的形成。现在，一种X射线技术取得了进展，该技术能够以10微秒的分辨率实时监测金属中心的氧化还原和结构变化。我们发现，在氧气形成步骤中，会形成一种中间体——神秘的S4状态。其产生被确定为一个去质子化过程，而非预期的电子转移机制。随后的电子转移将产生另一种S4'状态，从而扩展了氧气形成的基本S状态循环。
