The determination of the structures of a series of serum glycoproteins from the Antarctic fish Trematomus borchgrevinki has been completed. These glycoproteins are present in a range of molecular weights and they consist entirely of repeating units of -Ala-Thr-Ala- in which threonine bears a disaccharide moiety that we now show to be a β-d-galactopyranosyl-(1→4)-2-acetamido-2-deoxy-α-d-galactopyranosyl moiety. To our knowledge this represents the first determination of the complete structure of a glycoprotein. These glycoproteins have been shown to be partly responsible for the unusually low temperatures at which the blood serums of Antarctic fishes freeze. We have prepared a series of derivatives of the glycoproteins in which hydroxyl groups of the carbohydrate moiety have been chemically modified by acetonation, acetylation or oxidation. The freezing point depressing activity of the derivatives has been evaluated and the results suggest that the activity results from an interaction with water or ice that involves many structural features of the glycoprotein molecules.
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