Reduction of the Mn cluster of the water-oxidizing enzyme by nitric oxide: formation of an S(-2) state.
Reduction of the Mn cluster of the water-oxidizing enzyme by nitric oxide: formation of an S(-2) state.
复制标题
一氧化氮还原水氧化酶的 Mn 簇：形成 S(-2) 态。
作者：
G. Schansker;C. Goussias;V. Petrouleas;A. William Rutherford
光系统 II 的放氧酶的锰簇在 -30°C 与一氧化氮相互作用时发生化学还原。形成的状态产生 S = 1/2 多线 EPR 信号 [Goussias, Ch., Ioannidis, N., and Petrouleas, V. (1997) Biochemistry 36, 9261]，该信号归因于 Mn(II)- Mn(III) 二聚体 [Sarrou, J.、Ioannidis, N.、Deligiannakis, Y. 和 Petrouleas, V. (1998) 生物化学 37, 3581]。在这项工作中，我们试图通过使用闪式测氧法、叶绿素 a 荧光和电子顺磁共振光谱来确定该状态是否可以归属于特定的还原 S 状态。使用 Joliot 型 O(2) 电极，在第六次或第七次闪光时观察到第一个最大析氧量。需要三次饱和预闪蒸才能将 NO 还原样品的闪蒸模式特征转换为未处理对照的闪蒸模式特征（即第三次闪蒸时 O(2) 演化最大值）。在 NO 处理的 PSII 中，与未处理的对照相比，S 状态依赖性叶绿素荧光水平的测量显示出三闪下移。在 EPR 研究中，在第四次闪光后观察到最大 S(2) 多线 EPR 信号。所有三种方法的结果都与大多数中心在用NO处理后处于对应于S(-2)状态的氧化还原状态的Mn簇一致。我们无法使用肼作为还原剂生成 Mn(II)-Mn(III) 多线信号；似乎S(-2)态Mn簇的化合价分布和可能的结构取决于所使用的还原剂的性质。
The manganese cluster of the oxygen-evolving enzyme of photosystem II is chemically reduced upon interaction with nitric oxide at -30 degrees C. The state formed gives rise to an S = 1/2 multiline EPR signal [Goussias, Ch., Ioannidis, N., and Petrouleas, V. (1997) Biochemistry 36, 9261] that is attributed to a Mn(II)- Mn(III) dimer [Sarrou, J., Ioannidis, N., Deligiannakis, Y., and Petrouleas, V. (1998) Biochemistry 37, 3581]. In this work, we sought to establish whether the state could be assigned to a specific, reduced S state by using flash oxymetry, chlorophyll a fluorescence, and electron paramagnetic resonance spectroscopy. With the Joliot-type O(2) electrode, the first maximum of oxygen evolution was observed on the sixth or seventh flash. Three saturating pre-flashes were required to convert the flash pattern characteristic of NO-reduced samples to that of the untreated control (i.e., O(2) evolution maximum on the third flash). Measurements of the S state-dependent level of chlorophyll fluorescence in NO-treated PSII showed a three-flash downshift compared to untreated controls. In the EPR study, the maximum S(2) multi-line EPR signal was observed after the fourth flash. The results from all three methods are consistent with the Mn cluster being in a redox state corresponding to an S(-2) state in a majority of centers after treatment with NO. We were unable to generate the Mn(II)-Mn(III) multi-line signal using hydrazine as a reductant; it appears that the valence distribution and possibly the structure of the Mn cluster in the S(-2) state are dependent on the nature of the reductant that is used.