Antifreeze Glycoproteins from an Antarctic Fish

A quasi-elastic light-scattering technique was used to study the hydrodynamic conformations of antifreeze glycoproteins from an Antarctic fish. Antifreeze glycoprotein is composed of repeating units of Ala-Ala-Thr, with each threonine O-linked to a disaccharide, and it exists as several polymers of different numbers of this repeating unit. Molecular weights of the two major active polymers are 10,500 and 17,500 by such methods as centrifugation and osmotic pressure, but <20 by freezing-point depression. Translational diffusion coefficients at 20” were 8.35 x lo-’ cm2 s-r and 6.15 x lo-’ cm2 s-r for the M,-10,500 and 17,500 polymers, respectively. Measurements at -0.2” in the presence of ice crystals did not indicate any conformational changes that might be related to the lowering of the freezing temperature. Lowering the temperature of these glycoprotein solutions close to temperatures of freezing caused a decrease in the effective hydrodynamic radius of both active and inactive glycoprotein components.