Comparison of antifreeze glycopeptides from arctic and antarctic fishes

Antifreeze glycopeptides from the Atlantic tomcod Microgadus tomcod), saffron cod (Eleginus gracilis), and Greenland cod (Gadus ogac) were isolated by ion exchange chromatography. Polyacrylamide gel electrophoresis revealed that fewer sizes of antifreeze glycopeptides are present in the serum of M. tomcod and E. gracilis compared to the Antarctic nototheniid (Dissostichus mawsoni), Glycopeptide 6 from M. tomcod and E. gracilis as well as glycopeptide 8 from G. ogac were sequenced and compared with known sequences of similar‐sized glycopeptides from Antarctic fishes. It was found that arginine residues in glycopeptide 6 from E. gracilis and M. tomcod occur at positions 15 and 18, that proline periodically replaces alanine (ala) at positions 7, 13, and 19. In contrast, none of the antifreeze glycopeptides from Antarctic fishes contain arginine. Threonine (thr) occupies positions 15 and 18 instead. Glycopeptide 8 from G. ogac was found to have the same sequence as glycopeptide 8 from the polar cod (Boreogadus saida). The results indicate that the repeating sequence (ala‐ala‐thr) appears to be highly conserved within polar fishes. However, greater variation in antifreeze glycopeptide structure exists within one family of northern cods (Gadidae) than within species belonging to four separate families of Antarctic fishes.