ANTIFREEZE PROTEINS

Many species of fish which inhabit the polar oceans have antifreeze proteins in their body fluids to prevent them from freezing. There are two groups of antifreeze proteins: the antifreeze glycoproteins (AFGPs) and the antifreeze proteins (AFPs). The primary structure of the AGFPs is a repeating (Ala-Ala-Thr) sequence with a disaccharide attached to the threonine residue. The AFPs have various structures. Type I AFPs have an alpha-helical stucture, whereas Type II and III have some unusual secondary structures. It is believed that antifreeze proteins depress freezing point by attaching to ice crystals and interfering with water molecules joining the ice lattice. Recent computer modelling suggests, at least for one antifreeze peptide, that the molecules are arranged in an antiparallel fashion with co-operative side-to-side binding. Several workers have produced antifreeze peptides either chemically or by recombinant DNA techniques. Synthetic antifreeze peptides have been shown to have practical applications, including use in foods.