Jansson Helén, Bergman Rikard, Swenson Jan
Department of Applied Physics, Chalmers University of Technology, SE-412 96 Göteborg, Sweden.
J Phys Chem B. 2005 Dec 22;109(50):24134-41. doi: 10.1021/jp052418v.
We present results obtained by dielectric spectroscopy in wide frequency (10(-2)-10(9) Hz) and temperature ranges on human hemoglobin in the three different solvents water, glycerol, and methanol, at a solvent level of 0.8 g of solvent/g of protein. In this broad frequency region, there are motions on several time-scales in the measured temperature range (110-370 K for water, 170-410 K for glycerol, and 110-310 K for methanol). For all samples, the dielectric data shows at least four relaxation processes, with frequency dependences that are well described by the Havriliak-Negami or Cole-Cole functions. The fastest and most pronounced process in the dielectric spectra of hemoglobin in glycerol and methanol solutions is similar to the alpha-relaxation of the corresponding bulk solvent (but shifted to slower dynamics due to surface interactions). For water solutions, however, this process corresponds to earlier results obtained for water confined in various systems and it is most likely due to a local beta-relaxation. The slowing down of the glycerol and methanol relaxations and the good agreement with earlier results on confined water show that this process is affected by the interaction with the protein surface. The second fastest process is attributed to motions of polar side groups on the protein, with a possible contribution from tightly bound solvent molecules. This process is shifted to slower dynamics with increasing solvent viscosity, and it shows a crossover in its temperature dependence from Arrhenius behavior at low temperatures to non-Arrhenius behavior at higher temperatures where there seems to be an onset of cooperativity effects. The origins of the two slowest relaxation processes (visible at high temperatures and low frequencies), which show saddlelike temperature dependences for the solvents water and methanol, are most likely due to motions of the polypeptide backbone and an even more global motion in the protein molecule.
我们展示了通过介电谱在宽频率范围（10⁻² - 10⁹ Hz）和温度范围内，在三种不同溶剂（水、甘油和甲醇）中，溶剂与蛋白质质量比为0.8 g溶剂/g蛋白质的条件下，对人血红蛋白所获得的结果。在这个宽频率区域内，在所测量的温度范围（水为110 - 370 K，甘油为170 - 410 K，甲醇为110 - 310 K）存在多个时间尺度的运动。对于所有样品，介电数据显示至少有四个弛豫过程，其频率依赖性可以用Havriliak - Negami函数或Cole - Cole函数很好地描述。在甘油和甲醇溶液中血红蛋白的介电谱中，最快且最明显的过程类似于相应本体溶剂的α弛豫（但由于表面相互作用而向较慢动力学方向移动）。然而，对于水溶液，这个过程与在各种体系中受限水所获得的早期结果相对应，并且很可能是由于局部β弛豫。甘油和甲醇弛豫的减慢以及与受限水早期结果的良好一致性表明，这个过程受到与蛋白质表面相互作用的影响。第二快的过程归因于蛋白质上极性侧基的运动，可能还有紧密结合的溶剂分子的贡献。随着溶剂粘度增加，这个过程向较慢动力学方向移动，并且其温度依赖性在低温下从阿仑尼乌斯行为转变为高温下的非阿仑尼乌斯行为，在高温下似乎出现了协同效应。两个最慢弛豫过程（在高温和低频下可见）的起源，对于水和甲醇溶剂呈现鞍状温度依赖性，很可能是由于多肽主链的运动以及蛋白质分子中更全局的运动。
