Nitschke W, Feiler U, Rutherford A W
Service de Biophysique, Département de Biologie, CEN Saclay, Gif sur Yvette, France.
Biochemistry. 1990 Apr 24;29(16):3834-42. doi: 10.1021/bi00468a005.
Membrane preparations of two species of the green sulfur bacteria Chlorobium have been studied by EPR. Three signals were detected which were attributed to iron-sulfur centers acting as electron acceptors in the photosynthetic reaction center. (1) A signal from a center designated FB, (gz = 2.07, gy = 1.91, gx = 1.86) was photoinduced at 4 K. (2) A similar signal, FA (gz = 2.05, gy = 1.94, gx = 1.88), was photoinduced in addition to the FB signal upon a short period of illumination at 200 K. (3) Further illumination at 200 K resulted in the appearance of a broad feature at g = 1.78. This is attributed to the gx component of an iron-sulfur center designated FX. The designations of these signals as FB, FA, and FX are based on their spectroscopic similarities to signals in photosystem I (PS I). The orientation dependence of these EPR signals in ordered Chlorobium membrane multilayers is remarkably similar to that of their PS I homologues. A magnetic interaction between the reduced forms of FB and FA occurs, which is also very similar to that seen in PS I. However, in contrast to the situation in PS I, FA and FB cannot be chemically reduced by sodium dithionite at pH 11. This indicates redox potentials for FA and FB which are lower by at least 150 mV than their PS I counterparts. The triplet state of P840, the primary electron donor, could be photoinduced at 4 K in samples which had been preincubated with sodium dithionite and methyl viologen and then preilluminated at 200 K.(ABSTRACT TRUNCATED AT 250 WORDS)
通过电子顺磁共振（EPR）对绿硫细菌绿菌属的两个物种的膜制剂进行了研究。检测到三种信号，这些信号归因于在光合反应中心作为电子受体的铁硫中心。（1）在4K时光诱导出一个来自标记为FB的中心的信号（gz = 2.07，gy = 1.91，gx = 1.86）。（2）在200K下短时间光照后，除了FB信号外，还光诱导出一个类似的信号FA（gz = 2.05，gy = 1.94，gx = 1.88）。（3）在200K下进一步光照导致在g = 1.78处出现一个宽峰。这归因于标记为FX的铁硫中心的gx分量。这些信号被命名为FB、FA和FX是基于它们与光系统I（PS I）中信号的光谱相似性。这些EPR信号在有序的绿菌属膜多层中的取向依赖性与它们在PS I中的同源物非常相似。FB和FA的还原形式之间存在磁相互作用，这也与PS I中观察到的非常相似。然而，与PS I的情况相反，在pH 11时，FA和FB不能被连二亚硫酸钠化学还原。这表明FA和FB的氧化还原电位比它们在PS I中的对应物至少低150 mV。在已用连二亚硫酸钠和甲基紫精预孵育然后在200K下预光照的样品中，在4K时可以光诱导初级电子供体P840的三重态。（摘要截短于250字）
