Characterization of glycoprotein obtained from the skin mucus of an Antarctic fish, Trematomus bernacchii

The epithelial secretions were collected by scraping the skin of Trematomus bernacchii and seven species of temperate-water fishes and examined for the mucous glycoproteins by gel filtration on a Sepharose CL-4B column. In most cases, the glycoproteins were excluded at the void volume and separated from other mucous constitutents. The yields of the glycoproteins resolved were usually high (35-45%) in the following fishes secreting large quantities of thick mucus from their epidermis: Callionymus lunatus, Misgurnus anguillicaudatus, Anguilla japonica and Leiognathus nuchalis. A fish with hard scales, Carassius auratus, gave a mucous glycoprotein in a low yield (8.4%). Similarly, the glycoproteins of T. bernacchii, Trachurus japonicus and Acanthogobius fiavimanus were obtained in their respective yields of 17.5%, 18.9%, and 14.2%. The carbohydrate composition of the mucous glycoprotein in T. bernacchii was determined to consist of N-acetylneuraminic acid, N-acetylgalactosamine, galactose, mannose, fucose and glucose by analytical methods including thin-layer chromatography, high-performance liquid chromatography and gas-liquid chromatography. The molar ratio of N-acetylneuraminic acid, N-acetylgalactosamine and galactose (1.0:4.8:1.2) suggests that major carbohydrate chains are constituted by such mono- and disaccharide units as JV-acetylgalactosamine, N-acetylneuraminyl-N-acetylgalactosamine, and galactosyl-N-acetylgalactosamine. These carbohydrate units may link through O-glycosidic linkage to threonine and serine residues in the core polypeptide. Assuming such a structure of the carbohydrate unit, it becomes probable that the mucous glycoprotein secreted from T. bernacchii epithelial tissue has a similar ability to depress freezing point for the antifreeze glycoproteins present in the serum