Boussac A, Kuhl H, Ghibaudi E, Rögner M, Rutherford A W
Section de Bioénergétique, URA CNRS 2096, Département de Biologie Cellulaire et Moléculaire, CEA Saclay, Gif-sur-Yvette, France.
Biochemistry. 1999 Sep 14;38(37):11942-8. doi: 10.1021/bi990845r.
The Mn(4)-cluster of photosystem II (PSII) from Synechococcus elongatus was studied by electron paramagnetic resonance (EPR) spectroscopy after a series of saturating laser flashes given in the presence of either methanol or ethanol. Results were compared to those obtained in similar experiments done on PSII isolated from plants. The flash-dependent changes in amplitude of the EPR multiline signals were virtually identical in all samples. In agreement with earlier work [Messinger, J., Nugent, J. H. A., and Evans, M. C. W. (1997) Biochemistry 36, 11055-11060; Ahrling, K. A., Peterson, S., and Styring, S. (1997) Biochemistry 36, 13148-13152], detection of an EPR multiline signal from the S(0) state in PSII from plants was only possible with methanol present. In PSII from S. elongatus, it is shown that the S(0) state exhibits an EPR multiline signal in the absence of methanol (however, ethanol was present as a solvent for the artificial electron acceptor). The hyperfine lines are better resolved when methanol is present. The S(0) multiline signals detected in plant PSII and in S. elongatus were similar but not identical. Unlike the situation seen in plant PSII, the S(2) state in S. elongatus is not affected by the addition of methanol in that (i) the S(2) multiline EPR signal is not modified by methanol and (ii) the spin state of the S(2) state is affected by infrared light when methanol is present. It is also shown that the magnetic relaxation properties of an oxidized low-spin heme, attributed to cytochrome c(550), vary with the S states. This heme then is in the magnetic environment of the Mn(4) cluster.
在甲醇或乙醇存在的情况下，对细长聚球藻光系统II（PSII）的Mn(4)簇进行了一系列饱和激光闪光后，通过电子顺磁共振（EPR）光谱进行了研究。将结果与在从植物中分离出的PSII上进行的类似实验中获得的结果进行了比较。所有样品中EPR多线信号幅度的闪光依赖性变化几乎相同。与早期工作一致[梅西格，J.，纽金特，J. H. A.，和埃文斯，M. C. W.（1997年）《生物化学》36卷，第11055 - 11060页；阿林，K. A.，彼得森，S.，和斯廷，S.（1997年）《生物化学》36卷，第13148 - 13152页]，只有在存在甲醇的情况下，才能检测到来自植物PSII中S(0)态的EPR多线信号。在细长聚球藻的PSII中，结果表明，在不存在甲醇的情况下，S(0)态也会出现EPR多线信号（不过，乙醇作为人工电子受体的溶剂存在）。当存在甲醇时，超精细线的分辨率更高。在植物PSII和细长聚球藻中检测到的S(0)多线信号相似但不完全相同。与植物PSII中的情况不同，细长聚球藻中的S(2)态不受甲醇添加的影响，即（i）S(2)多线EPR信号不会因甲醇而改变，（ii）当存在甲醇时，S(2)态的自旋状态会受到红外光的影响。还表明，归因于细胞色素c(550)的氧化态低自旋血红素的磁弛豫特性会随S态而变化。因此，这种血红素处于Mn(4)簇的磁环境中。
