Elliott J I, Ljungdahl L G
J Bacteriol. 1982 Jul;151(1):328-33. doi: 10.1128/jb.151.1.328-333.1982.
A second ferredoxin protein was isolated from the thermophilic anaerobic bacterium Clostridium thermoaceticum and termed ferredoxin II. This ferredoxin was found to contain 7.9 +/- 0.3 iron atoms and 7.4 +/- 0.4 acid-labile sulfur atoms per mol of protein. Extrusion studies of the iron-sulfur centers showed the presence of two [Fe4-S4] centers per mol of protein and accounted for all of the iron present. The absorption spectrum was characterized by maxima at 390 nm (epsilon 390 = 30,400 M-1cm-1) and 280 nm (epsilon 280 = 41.400 M-1 cm-1) and by a shoulder at 300 nm. The ration of the absorbance of the pure protein at 390 nm to the absorbance at 280 nm was 0.74. Electron paramagnetic resonance data showed a weak signal in the oxidized state, and the reduced ferredoxin exhibited a spectrum typical of [Fe4-S4] clusters. Double integration of the reduced spectra showed that two electrons were necessary for the complete reduction of ferredoxin II. Amino histidine, and 1 arginine, and a molecular weight of 6,748 for the native protein. The ferredoxin is stable under anaerobic conditions for 60 min at 70 degrees C. The average oxidation-reduction potential for the two [Fe4-S4] centers was measured as -365 mV.
从嗜热厌氧细菌热醋梭菌中分离出了第二种铁氧化还原蛋白，并将其命名为铁氧化还原蛋白II。发现这种铁氧化还原蛋白每摩尔蛋白质含有7.9±0.3个铁原子和7.4±0.4个酸不稳定硫原子。对铁硫中心的挤出研究表明，每摩尔蛋白质存在两个[Fe4-S4]中心，且这解释了所有存在的铁。吸收光谱的特征在于在390nm（ε390 = 30400 M-1cm-1）和280nm（ε280 = 41400 M-1 cm-1）处有最大值，以及在300nm处有一个肩峰。纯蛋白质在390nm处的吸光度与在280nm处的吸光度之比为0.74。电子顺磁共振数据表明在氧化态下有一个微弱信号，还原型铁氧化还原蛋白呈现出典型的[Fe4-S4]簇的光谱。对还原光谱的双积分表明，铁氧化还原蛋白II完全还原需要两个电子。含有氨基组氨酸和1个精氨酸，天然蛋白质的分子量为6748。该铁氧化还原蛋白在厌氧条件下于70℃稳定60分钟。测得两个[Fe4-S4]中心的平均氧化还原电位为-365 mV。
