Zelent Bogumil, Bryan Michael A, Sharp Kim A, Vanderkooi Jane M
The Johnson Research Foundation, Department of Biochemistry and Biophysics, School of Medicine, Philadelphia PA 19104, United States.
Biophys Chem. 2009 May;141(2-3):222-30. doi: 10.1016/j.bpc.2009.02.002. Epub 2009 Feb 14.
The influence of proteins and solutes on hysteresis of freezing and melting of water was measured by infrared (IR) spectroscopy. Of the solutes examined, poly-L-arginine and flounder antifreeze protein produced the largest freezing point depression of water, with little effect on the melting temperature. Poly-L-lysine, poly-L-glutamate, cytochrome c and bovine serum albumin had less effect on the freezing of water. Small compounds used to mimic non-polar (trimethylamine N-oxide, methanol), positively charged (guanidinium chloride, NH(4)Cl, urea) and negatively charged (Na acetate) groups on protein surfaces were also examined. These molecules and ions depress water's freezing point and the melting profiles became broad. Since infrared absorption measures both bulk solvent and solvent bound to the solutes, this result is consistent with solutes interacting with liquid water. The amide I absorption bands of antifreeze protein and poly-L-arginine do not detectably change with the phase transition of water. An interpretation is that the antifreeze protein and poly-L-arginine order liquid water such that the water around the group is ice-like.
通过红外光谱法测定了蛋白质和溶质对水的凝固和熔化滞后现象的影响。在所研究的溶质中，聚-L-精氨酸和比目鱼抗冻蛋白使水的冰点降低幅度最大，而对熔化温度影响较小。聚-L-赖氨酸、聚-L-谷氨酸、细胞色素c和牛血清白蛋白对水的凝固影响较小。还研究了用于模拟蛋白质表面非极性（氧化三甲胺、甲醇）、带正电荷（氯化铵、氯化铵、尿素）和带负电荷（醋酸钠）基团的小分子化合物。这些分子和离子降低了水的冰点，且熔化曲线变宽。由于红外吸收测量的是大量溶剂以及与溶质结合的溶剂，因此该结果与溶质与液态水相互作用一致。抗冻蛋白和聚-L-精氨酸的酰胺I吸收带不会随着水的相变而发生可检测到的变化。一种解释是，抗冻蛋白和聚-L-精氨酸使液态水有序排列，使得该基团周围的水呈冰状。
