Boussac A, Sugiura M, Inoue Y, Rutherford A W
Section de Bioénergétique, DBCM, URA CNRS 2096, CEA Saclay, 91191 Gif sur Yvette Cedex, France.
Biochemistry. 2000 Nov 14;39(45):13788-99. doi: 10.1021/bi001159r.
The Mn(4)-cluster and the cytochrome c(550) in histidine-tagged photosystem II (PSII) from Synechococcus elongatus were studied using electron paramagnetic resonance (EPR) spectroscopy. The EPR signals associated with the S(0)-state (spin = 1/2) and the S(2)-state (spin = 1/2 and IR-induced spin = 5/2 state) were essentially identical to those detected in the non-His-tagged strain. The EPR signals from the S(3)-state, not previously reported in cyanobacteria, were detectable both using perpendicular (at g = 10) and parallel (at g = 14) polarization EPR, and these signals are similar to those found in plant PSII. In the S(3)-state, near-infrared illumination at 50 K induced a 176-G-wide split signal at g = 2 and signals at g = 5.20 and g = 1.51. These signals differ slightly from those reported in plant PSII [Ioannidis, N., and Petrouleas, V. (2000) Biochemistry 39, 5246-5254]. In accordance with the cited work, the split signal presumably reflects a radical interacting with the Mn(4)-cluster in a fraction of centers, while the g = 5.20 and g = 1.51 signals are tentatively attributed to a high-spin state of the Mn(4)-cluster with zero field splitting parameters different from those in plant PSII, reflecting minor changes in the environment of the Mn(4)-cluster. Biochemical modifications (Sr(2+)/Ca(2+) substitution, acetate and NH(3) treatments) were also investigated. In Sr(2+)-reconstituted PSII, in addition to the expected modified S(2) multiline signal, a signal at g = 5.2 was present instead of the g approximately 4 signal seen in plant PSII. In NH(3)-treated samples, in addition to the expected modified S(2)-multiline signal, a g approximately 4 signal was detected in a small proportion of the reaction centers. This is of note since g approximately 4 spectra arising from the Mn(4)-cluster in the S(2) state have not yet been published in cyanobacterial PSII. The detection of modified S(3)-signals in both perpendicular (at g = 7.5) and parallel (at g = 12) polarization EPR from NH(3)-treated PSII indicate that NH(3) is still bound in the S(3)-state. The acetate-treated PSII behaves essentially as in plant PSII. A study using oriented samples indicated that the heme plane of the oxidized low spin Cytc(550) was perpendicular to the plane of the membrane.
利用电子顺磁共振（EPR）光谱研究了来自聚球藻的组氨酸标记光系统II（PSII）中的Mn(4)-簇和细胞色素c(550)。与S(0)态（自旋 = 1/2）和S(2)态（自旋 = 1/2且红外诱导自旋 = 5/2态）相关的EPR信号与在无组氨酸标签菌株中检测到的信号基本相同。来自S(3)态的EPR信号（以前在蓝细菌中未报道），使用垂直（g = 10）和平行（g = 14）极化EPR均可检测到，并且这些信号与植物PSII中的信号相似。在S(3)态下，50 K的近红外光照在g = 2处诱导出一个176 G宽的分裂信号，在g = 5.20和g = 1.51处也有信号。这些信号与植物PSII中报道的信号略有不同[Ioannidis, N., and Petrouleas, V. (2000) Biochemistry 39, 5246 - 5254]。根据引用的工作，分裂信号可能反映了在一部分中心中与Mn(4)-簇相互作用的自由基，而g = 5.20和g = 1.51信号暂时归因于Mn(4)-簇的高自旋态，其零场分裂参数与植物PSII中的不同，反映了Mn(4)-簇环境的微小变化。还研究了生化修饰（Sr(2+)/Ca(2+)替代、乙酸盐和NH(3)处理）。在Sr(2+)重构的PSII中，除了预期的修饰S(2)多线信号外，在g = 5.2处出现了一个信号，而不是植物PSII中看到的g约为4的信号。在NH(3)处理的样品中，除了预期的修饰S(2)-多线信号外，在一小部分反应中心中检测到了g约为4的信号。这一点值得注意，因为来自S(2)态Mn(4)-簇的g约为4光谱尚未在蓝细菌PSII中发表。从NH(3)处理的PSII的垂直（g = 7.5）和平行（g = 12）极化EPR中检测到修饰的S(3)信号，表明NH(3)在S(3)态下仍然结合。乙酸盐处理的PSII的行为与植物PSII基本相同。一项使用取向样品的研究表明，氧化的低自旋Cytc(550)的血红素平面垂直于膜平面。
