Adding to the antifreeze agenda

Antifreeze proteins allow certain organisms with no thermal control to survive cold conditions, the best known examples to date coming from fish. Papers elsewhere in this issue1,2,3 now

describe the characterization of such proteins from grass and two species of insect. They provide insights into the mysterious ways that antifreeze proteins work.

The biological ‘antifreezes’ are solutes that stick to ice crystals in supercooled water and prevent their growth. (Supercooling refers to liquids below their freezing points; water is

easily supercooled to several degrees Celsius below freezing, and remains liquid indefinitely unless nucleated.) So these molecules are unlike the antifreezes used in internal combustion

engines, which lower the freezing point by changing the properties of liquid water. As surface-active materials, small quantities of antifreeze proteins can have large effects on surface

phenomena such as crystal growth. Antifreezes from cold-water fish range upwards in relative molecular mass from 2,600, and the most active prevent ice-crystal growth over a supercooling

temperature range of just over 1 °C. In combination with dissolved salts, this is enough to protect the fish from freezing in sea water at its freezing point of −1.9 °C.

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