Isolation and structures of glycoprotein-derived free sialooligosaccharides from the unfertilized eggs of Tribolodon hakonensis, a dace. Intracellular accumulation of a novel class of biantennary disialooligosaccharides.

Novel acidic oligosaccharides were isolated in abnormally large amounts (about 200 ng/egg) from the unfertilized eggs of Tribolodon hakonensis (a dace, "ugui" in Japanese). The free oligosaccharides were found to consist of a mixture of disialylated species most of which end with beta-mannosyl N-acetylglucosamine structure at their reducing termini, i.e. greater than Man beta 1-4GlcNAc. A minute portion of the sialooligosaccharides was found to have the reducing terminal structure, di-N-acetylchitobiose, i.e. greater than Man beta 1-4GlcNAc beta 1-4GlcNAc. From the structural analysis of these free sialooligosaccharides, the following structures are proposed: (sequence; see text) Occurrence of such a symmetrically or dissymmetrically branched form of the biantennary nonreducing periphery as revealed here is novel. Although it is unknown why and how such high amounts of free oligosaccharides are accumulated in unfertilized eggs, these were presumably protein-linked components and must be released at certain stages of oogenesis.