Bágel'ová J, Antalík M, Tomori Z
Department of Biophysics, Slovak Academy of Sciences, Kosice, Slovakia.
Biochem Mol Biol Int. 1997 Nov;43(4):891-900. doi: 10.1080/15216549700204701.
The effect of saturated solutions of polyglutamate on the thermal stabilities of the Met-80-heme iron bond and of the ferricytochrome c as a whole were studied by absorption spectroscopy and differential scanning calorimetry at pH 7.0. According to spectral data the midtransition temperature of the cleavage of the sulfur-iron bond was 57.4 +/- 0.5 degrees C and 66.8 +/- 0.5 degrees C for cytochrome c and cytochrome c-polyglutamate complex, respectively. Addition of polyglutamate to cytochrome c at pH 7.0 alters the denaturation properties of the protein. As follows from DSC scans, the denaturation temperature for cytochrome c is decreased from 85.4 +/- 0.2 degrees C to 68.7 +/- 0.2 degrees C in the presence of the saturated amount of polyglutamate. The protein stability in terms of Gibbs energy change at protein unfolding amount to delta G(25 degrees C) = 22.7 +/- 2.7 and 32.0 +/- 2.2 kJ/mol, for cytochrome c and cytochrome c-polyglutamate complex, respectively, at pH 7.0. It is evident that polyglutamate increases the thermal stability of the sulfur-iron bond and decreases the denaturation temperature of the cytochrome c molecule as a whole. The complex thermal stability in terms of Gibbs energy is not lower than that of cytochrome c in the range of physiological temperatures.
在pH 7.0条件下，通过吸收光谱法和差示扫描量热法研究了聚谷氨酸饱和溶液对Met-80-血红素铁键以及整个铁细胞色素c热稳定性的影响。根据光谱数据，细胞色素c和细胞色素c-聚谷氨酸复合物中硫-铁键断裂的中间转变温度分别为57.4±0.5℃和66.8±0.5℃。在pH 7.0时向细胞色素c中添加聚谷氨酸会改变蛋白质的变性特性。从差示扫描量热法扫描结果可知，在存在饱和量聚谷氨酸的情况下，细胞色素c的变性温度从85.4±0.2℃降至68.7±0.2℃。在pH 7.0时，就蛋白质展开时吉布斯自由能变化而言，细胞色素c和细胞色素c-聚谷氨酸复合物的蛋白质稳定性分别为ΔG(25℃)=22.7±2.7和32.0±2.2 kJ/mol。显然，聚谷氨酸提高了硫-铁键的热稳定性，并降低了整个细胞色素c分子的变性温度。就吉布斯自由能而言，该复合物在生理温度范围内的热稳定性不低于细胞色素c。
