Roy Soham, Richert Ranko
Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287-1604, USA.
Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287-1604, USA.
Biochim Biophys Acta. 2014 Feb;1844(2):323-9. doi: 10.1016/j.bbapap.2013.11.011. Epub 2013 Nov 26.
Due to the interest in protein dynamics, there are numerous dielectric relaxation studies of proteins in water and in glass-forming aqueous solvents such as glycerol-water mixtures. In the regime of low frequencies, the inevitable dc-conductivity of such systems limits the resolution of dynamics that are slow compared with the solvent relaxation. Solutions of myoglobin in glycerol/water mixtures of various compositions are measured by dielectric spectroscopy in the frequency range from 10mHz to 10MHz. The resolution of low frequency modes is improved by two approaches: electrical 'cleaning' and the analysis of the derivative of the real component of permittivity, which shows no direct signature of dc-conductivity. Effects of internal interfacial polarization are also addressed by measuring the same solvents in confinement as well as mixed with glass beads. We find two processes, the structural relaxation of the solvent and the slower rotational mode of the protein, with no indication at even lower frequencies of a dielectric signature of fluctuations associated with protein dynamics.
由于对蛋白质动力学的关注，人们对蛋白质在水中以及在诸如甘油 - 水混合物等形成玻璃态的水性溶剂中的介电弛豫进行了大量研究。在低频区域，此类系统不可避免的直流电导率限制了与溶剂弛豫相比缓慢的动力学分辨率。通过介电谱在10mHz至10MHz频率范围内测量了肌红蛋白在各种组成的甘油/水混合物中的溶液。通过两种方法提高了低频模式的分辨率：电“净化”以及对介电常数实部导数的分析，该分析未显示直流电导率的直接特征。通过测量受限状态下的相同溶剂以及与玻璃珠混合的溶剂，也探讨了内部界面极化的影响。我们发现了两个过程，即溶剂的结构弛豫和蛋白质较慢的旋转模式，在更低频率下没有迹象表明存在与蛋白质动力学相关的波动介电特征。
