Fish Antifreeze Proteins

The antifreeze molecules allow icefish to live in subfreezing water by plugging gaps in existing small ice crystals and preventing the attachment of more ice molecules. Ice crystal growth is thus effectively stopped.

To survive, Antarctic fishes have developed proteins that act as antifreeze. These antifreeze proteins are a group of unique macromolecules that help some polar and subpolar marine bony fishes avoid freezing in their icy habitats. The proteins were discovered by Dr. Art DeVries from fish that he collected at McMurdo Station while he was a graduate student at Stanford University in the early 1960s.

Waters of the southern ocean are so cold that temperate and tropical fish would freeze if they were placed in this environment. The presence of salt in sea water allows it to remain liquid until about -1.9C, almost 2 degrees below the freezing temperature of freshwater. The antifreeze proteins, along with normal body salts, depress the freezing point of blood and body fluids to 2.5C, slightly below the freezing point of sea water. These proteins bind to and inhibit growth of ice crystals within body fluids through an absorption-inhibition process. The proteins attach to small ice crystals, stemming their growth. This mechanism that inhibits further growth of the ice crystal remains under study, but apparently Antarctic fish are able to survive with very small ice crystals present in their body fluids.

There may be several commercial applications of these antifreeze proteins. These compounds are about 300 times more effective in preventing freezing than conventional chemical antifreezes at the same concentrations. The effectiveness of the fish antifreeze proteins in inhibiting ice growth suggests that they could be used to prevent freezing of food and freezing injury in several applications. For example, they could be used in the cryopreservation of foods that normally are rendered inedible due to ice crystal damage or to engineer cold resistance in living plants, as well as for the cryopreservation of tissues and organs. The study of the mechanism of how antifreezes bind to ice and inhibit its growth also provides insights into how other biomolecules affect growth of such pathogenic (harmful) bio-crystals as those associated with gout, kidney, and gall stones. Lastly, these proteins may have applications as non-polluting de-icing agents. To date, NSF-funded investigators have successfully introduced two of the four different types of fish antifreeze proteins into yeast and bacteria through recombinant DNA technology. Using these cloned genes and molecular technology, researchers can produce large quantities of antifreeze proteins through large-scale fermentation.

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