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

TLDR

Antarctic fish produce glycoproteins that depress water’s freezing point beyond what particle count predicts, a phenomenon of interest for cryoprotection. The study aims to isolate and characterize these active glycoproteins responsible for the anomalous freezing‑point depression. Researchers extracted glycoproteins from the sera of Trematomus borchgrevinki and Dissostichus mawsoni, then separated them into three distinct groups using ion‑exchange chromatography and acrylamide gel electrophoresis, followed by viscosity, circular dichroism, and dialysis analyses. The active glycoproteins depress freezing point to the same extent as NaCl on a weight basis, are composed mainly of threonine, alanine, N‑acetylgalactosamine, and galactose, exist in equal amounts as three variants with molecular weights of 10,500, 17,000, and 21,500 Da, and are expanded molecules, whereas inactive glycoproteins differ only by the presence of proline.

Abstract

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.