Effects of Local Concentration on Freezing Solutions of Winter Flounder Antifreeze Protein

We have carried out experiments on the one-directional freezing of an aqueous solution of winter flounder antifreeze protein in a narrow gap between two cover glasses. The motion of the ice/solution interface has been observed with an inverted microscope. The solution has been cooled by a Peltier device. The local change in protein concentration has been estimated from the measured intensity of fluorescence from molecules tagged to the protein. It is found that highly-concentrated regions of the protein can be observed in the bottom edge of the serrated interface. These regions interact with the interface, though most of the protein diffuses due to the concentration gradient. The diffusion velocity is much lower than the interface velocity. Thus, the protein is accumulated near the interface.