Reddy K S, Angiolillo P J, Wright W W, Laberge M, Vanderkooi J M
Johnson Research Foundation, Department of Biochemistry & Biophysics, School of Medicine, University of Pennsylvania, Philadelphia 19104, USA.
Biochemistry. 1996 Oct 1;35(39):12820-30. doi: 10.1021/bi960895l.
The alpha or Q0,0 absorption band of horse iron(II) cytochrome c splits and shifts to the blue as temperature decreases over the temperature range of 290-10 K. At room temperature, its maximum is at 18 150 cm-1 and the spectral width is 273 cm-1, whereas at 10 K, the two bands of the Q0,0 transition occur at 18 364 and 18 253 cm-1 and the width of the lowest-energy band is 96 cm-1. Temperature dependent splitting also occurs for zinc cytochrome c, a derivative in which Fe has been replaced by Zn; at 10 K, the peaks in the Q0,0 band region occur at 17 106 and 16 996 cm-1. The peak positions are independent of the cryosolvent (aqueous ethylene glycol or glycerol mixtures). The splitting of the Q0,0 band seen in the protein (approximately 110 cm-1 for iron and zinc cytochrome c) is comparable to the crystal field splitting observed for metalloporphyrins in mixed crystals. In contrast, the Q0,0 band of zinc coproporphyrin III in a glassy solvent (dimethylformamide/ethylene glycol) or in poly(vinyl chloride) shows a blue shift with temperature decrease but no evidence of Q0,0 splitting. Available spectral data show that the Q0,0 band is composed of two nearly degenerate electronic transitions and the split is due to the asymmetry in the heme pocket of the protein that arises from the surrounding polypeptide chain. This asymmetry results in the stabilization of one form of the excited state over the other, according to a Jahn-Teller mechanism.
在290 - 10 K的温度范围内，随着温度降低，马亚铁细胞色素c的α或Q0,0吸收带会分裂并向蓝光方向移动。室温下，其最大值位于18150 cm-1，光谱宽度为273 cm-1，而在10 K时，Q0,0跃迁的两个谱带出现在18364和18253 cm-1处，最低能量谱带的宽度为96 cm-1。锌细胞色素c（一种铁被锌取代的衍生物）也会出现与温度相关的分裂；在10 K时，Q0,0谱带区域的峰值出现在17106和16996 cm-1处。峰值位置与冷冻溶剂（乙二醇或甘油的水溶液混合物）无关。在蛋白质中观察到的Q0,0谱带分裂（铁和锌细胞色素c约为110 cm-1）与混合晶体中金属卟啉的晶体场分裂相当。相比之下，玻璃态溶剂（二甲基甲酰胺/乙二醇）或聚氯乙烯中的锌原卟啉III的Q0,0谱带随着温度降低会出现蓝移，但没有Q0,0分裂的迹象。现有光谱数据表明，Q0,0谱带由两个近乎简并的电子跃迁组成，分裂是由于蛋白质血红素口袋中由周围多肽链引起的不对称性导致的。根据 Jahn - Teller 机制，这种不对称性导致一种激发态形式比另一种更稳定。
