Chemical and Physical Properties of Freezing Point-depressing Glycoproteins from Antarctic Fishes

Glycoproteins were isolated from the blood sera of the Antarctic fishes Trematomus borchgrevinki and Dissostichus mawsoni. Some of these glycoproteins have the unique property of depressing the freezing point of water more than expected on the basis of the number of particles present in solution and are termed active glycoproteins. These freezing point-depressing glycoproteins depress the freezing point of water to the same extent as NaCl on a weight basis. They are composed primarily of threonine (16%), alanine (23%), N-acetylgalactosamine (29%), and galactose (28%). Compared with the active glycoproteins, the inactive ones (which form ideal solutions) have approximately the same composition except that proline is present. The active glycoproteins have been separated into three distinct groups, based on results from ion exchange chromatography and acrylamide gel electrophoresis. The three active glycoproteins occur in equal amounts in the blood sera, have identical compositions on a weight basis, but differ in molecular weights (10,500,17,000 and 21,500 g). Studies of viscosity and circular dichroism and dialysis experiments indicate that the active glycoproteins are expanded molecules, a property which undoubtedly is of importance to their function.