Antifreeze proteins lower the blood freezing point. This fish lives in antarctic waters where it experiences water temperatures near -1.9 degrees Celsius. Its blood has a freezing point of about -2.0 degrees Celsius, and 30% of the freezing-point depression is due mainly to the 3 major high molecular weight glycoproteins in the plasma. O-linked glycans consist of Gal-GalNAc disaccharides. The three proteins may differ only in the number of repeating units of -Ala-Ala-Thr-. The two small glycopeptides are present in a much higher concentration (5 times by weight) than the HMW glycoproteins but produce only a small depression effect. The exact physiological role of the small glycopeptides is not known. The three major glycoproteins (3, 4, and 5) have the same N-terminal sequence, A-A-T-A-A-T, and C-terminal Ala. Each protein is composed only of Ala and Thr residues in a ratio of 2:1 and arranged in the repeating sequence -A-A-T-. The small glycopeptides 7 and 8 appear to contain 20 and 14 residues, respectively, and to have the same N-terminal sequence and C-terminal residue as the 3 major proteins. However, each has 2 Pro residues (instead of 1 of the Ala in each of 2 repeating units).