WHEN you put antifreeze in your car radiator, it lowers both the freezing and the melting point of the coolant. But living organisms have evolved a different sort of freeze protection. Their antifreeze lowers the freezing point without affecting the melting point.
For example, ice normally melts and water freezes at 32 degrees F. The special freeze protection of organisms would not affect the melting point but might lower the freezing point to, let's say hypothetically, 28 degrees F.
If biochemists can understand just how this freeze protection works, it should help them unravel the secret of how organic life survives at icy temperatures. It now appears that organisms using this kind of protection have antifreeze compounds that can radically alter the way ice crystallizes.
Animals as different as frogs, insects, and Arctic fish use some form of antifreeze. In some of them, this merely lowers the temperature at which ice forms in their bodies. Others follow a different strategy, in which ice is allowed to form outside the body cells.
Antifreeze within the cells themselves, such as glycerol, protects these vital units of organic life.
Charles A. Knight and Larry D. Oolman of the National Center for Atmospheric Research at Boulder, Colo., and Arthur L. DeVries of the University of Illinois have experimented with several of the compounds such animals use. They find that even minute amounts of these materials - called antifreeze glycoproteins (AFGP) - change the way ice crystallizes.
They report in Nature that the crystals form faces (planes) not normally seen. Also, their growth is restricted along one of the crystal axes. These effects suggest that the AFGP molecules bind to the ice in ways that may inhibit freezing.
Also, very small amounts of these compounds inhibit what is known as recrystallization. This is an effect that takes place after a solution has frozen. An agglomeration of small crystals tends to recrystallize in larger sizes.
In their paper, the three scientists suggest that inhibiting recrystallization might have some application to storage of frozen foods or medicines. Commenting on this, Knight explains that recrystallization is one way that frozen food may deteriorate.
Knight says that the AFGPs ''are absolutely spectacular in stopping recrystallization.''
But, he adds, ''The question is whether or not this is important practically.'' That would be something for a frozen-food specialist to determine. It is beyond the scope of the research in which he and his colleagues are interested.
What is important to them is the fact that the AFGPs do have a striking ability to alter ice crystallization. This probably is a key to how they depress the freezing point.
This effect, where the freezing point is lower than the melting point, produces what is known technically as a ''hysteresis gap.'' With that gap of a Celsius degree or so, ice neither freezes nor melts for periods of hours or days in laboratory experiments.
Somehow, this curiosity of physical chemistry has been turned to lifesaving advantage by animals that must endure cold climates.