MEASUREMENT OF GRAIN-GROWTH IN THE RECRYSTALLIZATION OF RAPIDLY FROZEN-SOLUTIONS OF ANTIFREEZE GLYCOPROTEINS

A quantitative estimate of the activation energy for grain growth has been obtained by analyzing ice recrystallization experiments from wate r and from solutions with small amounts (< 1.0 mu g/mL) of antifreeze glycoprotein (AFGP). Rates of grain growth are measured as changes of grain diameter in time, with the supercooled holding temperature and g lycoprotein concentration as parameters. Arrhenius plots of these rate s vs (1/T) yielded slopes proportional to the activation energies for the particular species. The values of activation energy ace almost ind ependent of solution concentration or the species of AFGP. Averaged ac tivation energy value for the AFGP-4 species is Q(g) = (6.61 +/- 1.02) X 10(5) J/mole. The ''less active'' AFGP-8 yielded an average Q(g) = (5.71 +/- 2.39) X 10(5) J/mole, quite similar to the AFGP-4 species. T he activation energy for recrystallization in a pure ice-water system was estimated from two temperature points, T = -5.4 and -7.5 degrees C . The best value is 2.39 X 10(5) J/mole, nearly twice that obtained by M. N. Martino and N. E. Zaritsky [(1989) Cryobiology, Vol. 26, p. 138 ] in a recrystallization experiment using salt solution, but much smal ler than the values derived from the AFGP solutions. Results further s how that activation entropy is at least a factor of 2 larger for the A FGP species than that of pure ice-water system under the same growth c onditions. These results suggest significant roles, both energetically and entropically, for AFGP molecules in their ability to inhibit grai n growth of ice. (C) 1994 John Wiley and Sons, Inc.