Structure and Function of the Reaction Center Complexes from Green Sulfur Bacteria

研究了绿色硫光合细菌Chlorobium tepidum的细胞色素（Cyt）c_<551>和与纯化的反应中心（RC）结合的Fe-S中心（CF_A/CF_B）在室温下的闪光诱导光动力学。在551 nm处，闪光灯引起的吸光度变化衰减的t &lt;1/2&gt;为几百ms，1-甲氧基-5-甲基吩嗪硫酸甲酯（mPMS）加速了该衰减。在蓝区，吸光度变化由依赖于mPMS的组分（Cyt）和不依赖于mPMS的组分（CF_A/CF_B）组成，其衰减的t_（1/2）为-400-650 ms，后者的衰减被甲基紫精（-440 mV）和甲基紫精（-360 mV）有效地加速，而敌草快（-540 mV）的加速作用较小。Cyt c的差谱在551、-520和-420 nm处有负峰，在-440 ~-500 nm处有正峰。CF_A/CF_B的差光谱与PSI的P430相似，在430-435 nm处有一宽的负峰。光合系统I的F_A、F_B和F_X-铁硫中心A、B和X;叶绿素的CF_A、CF_B和CF_X-F_A-、F_B-和F_X-类铁硫中心; mPMS-1-甲氧基-5-甲基吩嗪鎓甲基硫酸盐，PSI-光系统I ; RC-反应中心

Flash-induced optical kinetics at room temperature of cytochrome (Cyt) c_<551> and an Fe-S center (CF_A/CF_B) bound to a purified reaction center (RC) complex from the green sulfur photosynthetic bacterium Chlorobium tepidum were studied. At 551 nm, the flash-induced absorbance change decayd with a t_<1/2> of several hundred ms, and the decay was accelerated by 1-methoxy-5-methylphenazinium methyl sulfate (mPMS). In the blue region, the absorbance change was composed of mPMS-dependent (Cyt) and mPMS-independent component (CF_A/CF_B) which decayd with a t_<1/2> of -400-650 ms. Decay of the latter was effectively accelerated by benzyl viologen (Em -360 mV) and methyl viologen (-440 mV), and less effectively by triquat (-540 mV). The difference spectrum of Cyt c had negative peaks at 551, -520 and -420 nm, with a positive rise a -440 to -500 nm. The difference spectrum of CF_A/CF_B resembled P430 of PSI,and had a broad negative peak at 430-435 nm.Abbreviations : (B) Chl- (bacterio) chlorophyll ; Cyt-cytochrome ; F_A, F_B and F_X-iron-sulfur center A,B and X of photosystem I ; CF_A, CF_B and CF_X-F_A-, F_B- and F_X-like Fe-S center of Chlorobium ; mPMS-1-methoxy-5-methylphenazinium methyl sulfate, PSI-Photosystem I ; RC-reaction center