Petersen J, Dekker J P, Bowlby N R, Ghanotakis D F, Yocum C F, Babcock G T
Department of Chemistry, Michigan State University, East Lansing 48824.
Biochemistry. 1990 Apr 3;29(13):3226-31. doi: 10.1021/bi00465a012.
A photosystem II complex consisting of a 47-kDa chlorophyll-binding protein (CP47), the reaction center proteins D1 and D2, and cytochrome b-559 was characterized. Trace amounts of plastoquinone were found, indicating that the primary acceptor quinone QA has been extracted during purification. However, in the presence of ferricyanide, an EPR signal with the characteristic line shape and g value of the tyrosine radicals associated with photosystem II could be photoaccumulated in the majority of the reaction centers; in the absence of ferricyanide, or under low-temperature illumination conditions, a 9.5-11-G wide signal with a Gaussian line shape was observed at g = 2.003. Neither signal is observed in D1-D2-b-559 complexes, indicating that retention of CP47 produces a more native, but quinone-depleted photosystem II reaction center. The tyrosine radical photogenerated at room temperature can be trapped at cryogenic temperatures; results are presented showing that this radical can arise from tyrosine YZ, from tyrosine YD, or from both species. Low-temperature EPR spectroscopy also revealed a pronounced split signal with contributions at g = 6.05 and g = 5.75, which is attributed to high-spin, non-heme Fe3+ with axial ligation symmetry which is probably the non-heme iron associated with the acceptor side of photosystem II.
对由一种47 kDa的叶绿素结合蛋白（CP47）、反应中心蛋白D1和D2以及细胞色素b - 559组成的光系统II复合物进行了表征。发现存在痕量的质体醌，这表明在纯化过程中初级受体醌QA已被提取。然而，在铁氰化物存在的情况下，与光系统II相关的具有酪氨酸自由基特征线形和g值的电子顺磁共振（EPR）信号可在大多数反应中心光积累；在没有铁氰化物的情况下，或在低温光照条件下，在g = 2.003处观察到一个具有高斯线形的9.5 - 11 G宽信号。在D1 - D2 - b - 559复合物中均未观察到这两种信号，这表明CP47的保留产生了一个更天然但醌耗尽的光系统II反应中心。在室温下光生成的酪氨酸自由基可在低温下被捕获；给出的结果表明该自由基可源自酪氨酸YZ、酪氨酸YD或两者。低温EPR光谱还揭示了一个明显的分裂信号，在g = 6.05和g = 5.75处有贡献，这归因于具有轴向配体对称性的高自旋、非血红素Fe3 +，其可能是与光系统II受体侧相关的非血红素铁。
