Antifreeze glycoproteins: relationship between molecular weight, thermal hysteresis and the inhibition of leakage from liposomes during thermotropic phase transition

Antifreeze glycoproteins (AFGP) were isolated and purified from the blood p lasma of rock cod (Gadus ogac), using DEAE-Bio-gel ion exchange chromatogra phy, followed by high performance liquid chromatography (HPLC). The purifie d proteins were analyzed using polyacrylamide gel electrophoresis (PAGE), a nd electrospray mass spectrometry. The results indicated that rock cod synt hesize seven size classes of glycoproteins, ranging from 2.6 to 24 kDa, wit h each size class containing multiple isoforms, Antifreeze activity, as det ermined by thermal hysteresis, indicated that the AFGP could be separated i nto two groups, with the larger size classes (molecular mass > 13 kDa) havi ng approximately 3-4 times the activity of the smaller, proline containing, size classes (molecular mass < 10 kDa). All of the AFGP size classes preve nted leakage From dielaidoylphosphatidylcholine (DEPC) liposomes as they we re cooled through their phase transition temperature, with the larger size classes being approximately 4 times as effective as the smaller ones. It is hypothesized that AFGP prevent liposomes from leaking as they pass through the phase transition temperature by binding to the phospholipid membrane. (C) 2001 Elsevier Science Inc. All rights reserved.