Four distinct macromolecular antifreezes have been isolated and characterized from different marine fish. These include the glycoprotein antifreezes (Mr 2.5-33 K), which are made up of a repeating tripeptide (Ala-Ala-Thr)n with a disaccharide attached to the threonyl residues, and three antifreeze protein (AFP) types. Type I is an alanine-rich, amphiphilic, alpha-helix (Mr 3-5 K); type II is a larger protein (Mr 14 K) with a high content of reverse turns and five disulfide bridges; and type III is intermediate in size (Mr 6-7 K) with no distinguishing features of secondary structure or amino acid composition. Despite their marked structural differences, all four antifreeze types appear to function in the same way by binding to the prism faces of ice crystals and inhibiting growth along the a-axes. It is suggested that type I AFP binds preferentially to the prism faces as a result of interactions between the helix macrodipole and the dipoles on the water molecules in the ice lattice. Binding is stabilized ...