Isolation, characterization, and physical properties of protein antifreezes from the winter flounder, Pseudopleuronectes americanus

1. 1. Three proteins with an unusual ability to depress the freezing point of water have been purified from the blood serum of the winter flounder, Pseudopleuronectes americanus. 2. 2. The amino acid compositions of these proteins are essentially the same and consist of large amounts of alanine, threonine and aspartic acid. 3. 3. The flounder protein antifreeze is quite different compositionally from the glycoprotein antifreeze previously isolated from antarctic nototheniid fishes. Therefore it seems that macromolecular antifreeze solutes have evolved independently in fishes at least twice.