Dependence of freeze-concentration inhibition on antifreeze protein

The ability for freeze-concentration inhibition (FCI) was examined for type I antifreeze protein (AFPI)and antifreeze glycoprotein (AFGP)through the observation of the condensation of red-colored ink in an ice block for various concentrations of the proteins. The thermal hysteresis (TH), which indicates the ice growth inhibition strength, and ice-shaping ability were also examined for the two samples. The amount of AFPI and AFGP necessary for FCI was determined to be 0.1 mg/ml and 0.25 mg/ml, respectively. There was no significant difference in the TH of both samples. AFPI and AFGP shaped the ice crystals into hexagonal trapezohedrons and hexagonal bipyramids, respectively, where the former was thinner than the latter. These results suggest that a principle determinant of FCI is the ice-shaping ability, rather than the ice growth inhibition of AFPs.