Department of Chemistry, Yale University, 06511, New Haven, CT, USA.
Photosynth Res. 1987 Jan;12(3):205-18. doi: 10.1007/BF00055121.
Electron paramagnetic resonance (EPR) spectroscopy and O2 evolution assays were performed on photosystem II (PSII) membranes which had been treated with 1 M CaCl2 to release the 17, 23 and 33 kilodalton (kDa) extrinsic polypeptides. Manganese was not released from PSII membranes by this treatment as long as a high concentration of chloride was maintained. We have quantitated the EPR signals of the several electron donors and acceptors of PSII that are photooxidized or reduced in a single stable charge separation over the temperature range of 77 to 240 K. The behavior of the samples was qualitatively similar to that observed in samples depleted of only the 17 and 23 kDa polypeptides (de Paula et al. (1986) Biochemistry25, 6487-6494). In both cases, the S2 state multiline EPR signal was observed in high yield and its formation required bound Ca(2+). The lineshape of the S2 state multiline EPR signal and the magnetic properties of the manganese site were virtually identical to those of untreated PSII membranes. These results suggest that the structure of the manganese site is unaffected by removal of the 33 kDa polypeptide. Nevertheless, in samples lacking the 33 kDa polypeptide a stable charge separation could only be produced in about one half of the reaction centers below 160 K, in contrast to the result obtained in untreated or 17 and 23 kDa polypeptide-depleted PSII membranes. This suggests that one function of the 33 kDa polypeptide is to stabilize conformations of PSII that are active in secondary electron transfer events.
电子顺磁共振（EPR）光谱和 O2 释放测定在经 1 M CaCl2 处理以释放 17、23 和 33 千道尔顿（kDa）的外向多肽的 PSII 膜上进行。只要保持高浓度的氯离子，锰就不会从 PSII 膜中释放出来。我们已经定量了 PSII 的几个电子供体和受体的 EPR 信号，这些电子供体和受体在 77 至 240 K 的温度范围内通过单个稳定的电荷分离被光氧化或还原。这些样品的行为与仅耗尽 17 和 23 kDa 多肽的样品（de Paula 等人，（1986）生物化学 25,6487-6494）观察到的行为相似。在这两种情况下，都观察到 S2 态多线 EPR 信号以高产率形成，其形成需要结合的 Ca(2+)。S2 态多线 EPR 信号的线形状和锰位点的磁性特性与未处理的 PSII 膜几乎相同。这些结果表明，锰位点的结构不受去除 33 kDa 多肽的影响。然而，在缺乏 33 kDa 多肽的样品中，在 160 K 以下的约一半反应中心中只能产生稳定的电荷分离，而在未处理或耗尽 17 和 23 kDa 多肽的 PSII 膜中得到的结果相反。这表明 33 kDa 多肽的一个功能是稳定 PSII 的构象，这些构象在次级电子转移事件中是活跃的。
