Magliozzo R S, McIntosh B A, Sweeney W V
J Biol Chem. 1982 Apr 10;257(7):3506-9.
The origin of the dependence of E1/2 on pH exhibited by Clostridium pasteurianum 2(4Fe-4S) ferredoxin has been investigated. The results show that oxidation state-dependent pK values, which may arise from sites on the iron-sulfur centers, are responsible for the pH effect. Based on a model of two equivalent protonation sites/molecule, values of 7.4 for pKox and 8.9 for pKrd were obtained. The results of experiments which monitor changes in the hydrogen ion concentration with changes in protein oxidation state are reported. The magnitude of the changes in pH on reduction or reoxidation of the protein are in reasonable agreement with the proposed model. The conformation of C. pasteurianum ferredoxin was examined by nmr, epr, and CD spectroscopies to rule out a pH-dependent conformation equilibrium as the origin of the pH effect.
对巴氏芽孢杆菌2(4Fe-4S)铁氧化还原蛋白所表现出的E1/2对pH的依赖性起源进行了研究。结果表明，可能源自铁硫中心位点的氧化态依赖性pK值是造成pH效应的原因。基于每个分子有两个等效质子化位点的模型，得到pKox值为7.4，pKrd值为8.9。报告了监测随着蛋白质氧化态变化氢离子浓度变化的实验结果。蛋白质还原或再氧化时pH变化的幅度与所提出的模型合理相符。通过核磁共振、电子顺磁共振和圆二色光谱对巴氏芽孢杆菌铁氧化还原蛋白的构象进行了检测，以排除pH依赖性构象平衡作为pH效应起源的可能性。
