Uemitsu N, Oashi H, Matsumiya H
J Biochem. 1975 Jul;78(1):229-34.
The line width of the NMR signal of water protons in solutions of native actomyosin and actomyosin denatured by heat, acetone or urea was measured over the temperature range from -10 degrees to below the freezing point. The line widths of the water band which increased exponentially with decreasing temperature were compared with each other and also with those of the corresponding control solution without actomyosin. The line broadening observed for native actomyosin solution on lowering the temperature was significantly smaller than that for heat-denatured actomyosin solution. This difference implies that this signal is sensitive to conformational perturbations of the protein. In addition, the temperature dependence of the line width for heat-, acetone-, or urea-denatured actomyosin solution was similar to that for the corresponding control solution. These phenomena can be interpreted in terms of the state of water associated with the hydrophobic and hydrophilic residues. Similar NMR studies of actomyosin solution containing dimethyl sulfoxide (DMSO) or dimethylformamide (DMF) showed that DMSO and DMF prevent the formation of ice crystals until about -70 degrees, suggesting that the cryoprotective effects of DMSO and DMF are due to the change in the state of water described above. These differences in temperature dependence between the sample and control solutions are well-correlated with the viscosity of the solution. This correlation is useful for elucidation of the mechanism of the protein denaturation.
在-10℃至冰点以下的温度范围内，测量了天然肌动球蛋白以及经加热、丙酮或尿素变性的肌动球蛋白溶液中水质子的核磁共振信号线宽。将随温度降低呈指数增加的水峰线宽相互比较，并与不含肌动球蛋白的相应对照溶液的线宽进行比较。降低温度时，天然肌动球蛋白溶液观察到的线宽展宽明显小于热变性肌动球蛋白溶液的线宽展宽。这种差异表明该信号对蛋白质的构象扰动敏感。此外，热变性、丙酮变性或尿素变性的肌动球蛋白溶液的线宽温度依赖性与相应对照溶液的相似。这些现象可以根据与疏水和亲水残基相关的水的状态来解释。对含有二甲基亚砜（DMSO）或二甲基甲酰胺（DMF）的肌动球蛋白溶液进行的类似核磁共振研究表明，DMSO和DMF可防止冰晶形成至约-70℃，这表明DMSO和DMF的冷冻保护作用是由于上述水状态的变化。样品溶液和对照溶液之间这些温度依赖性差异与溶液的粘度密切相关。这种相关性有助于阐明蛋白质变性的机制。
