Nugent J H, Doetschman D C, Maclachlan D J
Department of Biology, University College London, United Kingdom.
Biochemistry. 1992 Mar 24;31(11):2935-41. doi: 10.1021/bi00126a013.
We have compared the temperature-dependence characteristics of the EPR signals of Qa and Qb iron-semiquinones from both purple bacterial and plant photosystems. The data obtained were analyzed and estimates of the splitting parameters of the non-heme Fe2+ spin sublevels obtained. The study confirms the similarities of the g = 1.8 Qa iron-semiquinone signal (D/k = 15.6 K, E/k = 3.3 K) formed in formate-treated plant photosystem 2 to the signal found in purple bacteria. However, the g = 1.9 Qa iron-semiquinone signal (D/k = 7.1 K, E/k = much less than 1 K), formed in photosystem 2 when bicarbonate remains bound, has a unique temperature behavior. A series of spectral features associated with the iron-semiquinone in bicarbonate-bound photosystem 2 appear as the temperature is lowered, and the analysis of these data requires that some of these features be assigned to the higher spin states. The results are discussed in terms of the requirement for bicarbonate to be a ligand of the non-heme iron.
我们比较了来自紫色细菌和植物光系统的Qa和Qb铁半醌EPR信号的温度依赖性特征。对获得的数据进行了分析，并得到了非血红素Fe2+自旋子能级分裂参数的估计值。该研究证实，在甲酸盐处理的植物光系统2中形成的g = 1.8 Qa铁半醌信号（D/k = 15.6 K，E/k = 3.3 K）与在紫色细菌中发现的信号相似。然而，当碳酸氢盐保持结合状态时，在光系统2中形成的g = 1.9 Qa铁半醌信号（D/k = 7.1 K，E/k远小于1 K）具有独特的温度行为。随着温度降低，一系列与碳酸氢盐结合的光系统2中的铁半醌相关的光谱特征出现，对这些数据的分析要求将其中一些特征归因于较高的自旋态。根据碳酸氢盐作为非血红素铁配体的要求对结果进行了讨论。
