Antifreeze activity of Antarctic fish glycoprotein and a synthetic polymer

Abstract

Antifreeze glycoproteins (AFGPs) and proteins isolated from the sera of some polar fish species and overwintering insects are able to depress the freezing temperature of the aqueous body fluids (and of water) by means of a non-col ligative mechanism1,2. All previous measurements of the antifreeze effect have been performed on bulk samples under conditions where ice nucleation would be catalysed by participate impurities, giving limited and indeterminate degrees of undercooling. We report the first measurements of homogeneous (spontaneous) ice nucleation rates in deeply under-cooled (<233 K) solutions of AFGP and polyvinyl pyrrolidone (PVP), a well-characterized polymer which finds use as a cryoprotectant. Antifreeze activity is said3 to derive from the sorption of AFGP molecules on the active growth sites of ice crystals, preventing normal growth and inducing unusual crystal habits. We have performed experiments on the inhibition of ice crystal growth in solutions containing AFGP and PVP under standardized conditions, and find that the homogeneous nucleation and crystallization rates are sensitive to low concentrations of both substances, but AFGP is remarkably effective at inhibiting ice crystal growth.