Sialic acid-containing glycoprotein in the external mucus of eel, Anguilla japonica TEMMINCK et SCHLEGEL. V. Structure of disaccharide from eel skin mucous glycoprotein and its linkage to protein moiety.

Abstract

The purpose of this study was to elucidate the structure of disaccharide and the nature of its linkage to protein moiety of sialic acid-containing glycoprotein (SA-glycoprotein) isolated from eel skin mucus. The disaccharide of SA-glycoprotein was identified as N-acetylneuraminyl-(α, 2→6)-N-acetyl-galactosamine by periodate oxidation, analysis of the SMITH degradation product, and susceptibility to neuraminidase. The analysis of the sialic acid-containing glycopeptide which had been extensively digested with Pronase P showed that threonine and serine residues Were the only identifiable acceptors to the disaccharide units of eel SA-glycoprotein, indicating that the disaccharide units are O-glycosidically linked to the hydroxyl amino acids such as threonine and serine residues of SA-glycoprotein. This is the first, fish skin mucous glycoprotein which was elucidated concerning the structure of the carbohydrate unit and the carbohydrate-protein linkage. The function of eel SA-glycoprotein is also discussed.