Self oscillatory growth of ice crystal of ice in the antifreeze protein solution and its dynamics

在用荧光材料标记的抗冻糖蛋白分子溶液中进行了几种冰晶生长实验。冰的单向生长清楚地显示出生长速度的振荡和AFGP分子的周期性掺入，取决于生长速度。这是第一次在晶体内部直接观察到条纹的形成。冰单晶体的自由生长实验也显示出生长速率的振荡。利用衰减全反射型FTIR技术研究了AFGP分子在冰/水界面吸附状态下的二级结构(构象)。FTIR信号表明，AFGP分子在冰/水界面上以a-螺旋构象为主。由于溶液中分子的主要构象呈现随机状态，这一结果意味着分子的构象变化是为了强吸附到界面上。基于动力学环的概念，从生长速度与驱动力之间的滞后关系出发，建立了冰晶振荡生长的模型。该模型还提出AFGP分子在界面上的吸附应处于弱吸附和紧密吸附两种状态，这与ATR-FTIR实验结果一致，从而阐明了AFGP溶液中冰晶自振荡生长的动力学。了解AFGP分子吸附对晶体生长动力学的强烈影响，对于阐明这些蛋白质的抗冻功能具有重要意义。

Several kinds of ice crystal growth experiments were conducted in a solution of antifreeze glycoprotein molecules which were labeled by fluorescent material. One directional growth of ice clearly showed the oscillation of growth rates and periodic incorporation of AFGP molecules depending on the growth rate. This is the first direct observation of striation formation inside the crystal. Free growth experiments of ice single crystals also showed the oscillations of growth rates. The growth mode was ON-OFF type oscillation for the prismatic plane, whereas the continuous oscillation was observed for the basal plane.Secondary structures (conformations) of AFGP molecules under the adsorbed state at ice/water interface were examined using Attenuated Total Reflection type FTIR technique. The FTIR signal indicated that the AFGP molecules with a-helix conformation should be dominant at the ice/water interface. Since the dominant conformations of molecules in the solution showed the random state, this result means that the conformation change occur in order to strongly adsorb to the interface.A model to explain the oscillatory growth of ice crystal was also developed on the basis of the concept of kinetic loop, which was derived from the hysteresis relationships between the growth rate and the driving force. This model also suggest that the AFGP molecule adsorption on the interface should occur in two states, namely week adsorption state and tight adsorption state, which is consistent with the experimental result obtained by ATR-FTIR measurement.As a result, we clarified the dynamics of self-oscillatory growth of ice crystal in the AFGP solution. Understanding the crystal growth dynamics strongly affected by the adsorption of AFGP molecules will play an important role to clarify the antifreeze function of these proteins.