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

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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.