Antifreeze glycopeptides of antarctic fishes

Antifreeze glycoprotein levels in Antarctic notothenioid fishes inhabiting different thermal environments and the effect of warm acclimation

A quantification method was developed to determine the concentrations of the major antifreeze glycoprotein (AFGP) isoforms in the blood of Antarctic notothenioid fishes. Serum samples were precipitated with 2.5% TCA and the supernatant containing AFGPs were chromatographed on an HPLC size exclusion column and the concentrations of the major AFGP size classes were determined from the areas of the corresponding peaks in the elution profile. Eight species of Antarctic notothenioid fishes were examined and their blood AFGP concentrations varied from 5 to 35 mg/mL. All of these fishes synthesized both the large and small AFGPs, but maintained higher levels of small AFGPs than the large ones in their blood. The species inhabiting more severe water environments (lower temperature and presence of ice) had higher serum AFGP levels than those in milder environments. The cryopelagic Pagothenia borchgrevinki decreased their blood AFGP concentrations in response to warm acclimation, but to a much lower extent in comparison to the antifreeze-bearing fishes in the Northern Hemisphere. After being warm acclimated at +4 degrees C for 16 weeks, the serum concentrations of the small and large AFGPs were decreased by about 60% and 20%, respectively.

Antifreeze glycopeptides of the high-Antarctic silverfish Pleuragramma antarcticum (Notothenioidei)

Antifreeze glycopeptides (AFGP) have been isolated from the fully pelagic high-Antarctic silverfish Pleuragramma antarcticum of the suborder Notothenioidei (Perciformes). The fishes were caught during the PRV Polarstern expedition EPOS III (Jan-Mar, 1989) in the eastern and southeastern Weddell Sea. Glycoconjugate and amino acid analysis of antifreeze glycopeptides (AFGP) indicate that the glycopeptide structure is identical to the polymers of H2N[Ala-Ala(beta-galactosyl(1-->3)-alpha-N- acetylgalactosamine)Thr]nAla-Ala-COOH of previously studied Antarctic notothenioids. The content of AFGPs in P. antarcticum is lower than in other notothenioid fish from the same region. Antifreeze activity shows a maximal hysteresis of 1.19 degrees C at a concentration of 20 mg/ml AFGP. A linear increase in activity of the antifreeze glycopeptides could be demonstrated concomittant with a decreasing ice content. The freezing point of blood serum is -1.9 degrees C.