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

研究了绿硫光合细菌tepidum的细胞色素（Cyt） c_<551>和Fe-S中心（CF_A/CF_B）与纯化反应中心（RC）配合物结合的室温下闪致光学动力学。在551 nm处，闪致吸光度变化以t_<1/2>衰减数百ms， 1-甲氧基-5-甲基苯肼硫酸甲酯（mPMS）加速衰减。在蓝色区域，吸光度变化由mpms依赖性组分（Cyt）和非mpms依赖性组分（CF_A/CF_B）组成，其衰减时间为-400 ~ 650 ms， t_<1/2>。苯基紫紫素（Em -360 mV）和甲基紫紫素（-440 mV）能有效加速紫紫素的衰变，而三甘醇（-540 mV）对紫紫素的衰变效果较差。Cyt c的差谱在551、-520和-420 nm处呈负峰，在-440 ~ -500 nm处呈正上升。CF_A/CF_B的差谱与PSI的P430相似，在430 ~ 435 nm处有宽的负峰。缩写：(B) Chl-（细菌）叶绿素；Cyt-cytochrome;光系统I的F_A、F_B和f_x -铁硫中心A、B和X；氯藻的CF_A、CF_B和CF_X-F_A-、F_B-和f_x样Fe-S中心；mpms -1-甲氧基-5-甲基苯肼硫酸甲酯；RC-reaction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