ABSTRACT
Sialic acid-containing glycoconjugates, such as gangliosides and sialoglycoproteins, have been recognized to play important roles in many biological processes [l-5]. Sialyloligosaccharide chains of these glycoconjugates are exposed as ligands to the external environment, capable of expressing various biological functions, not only serving as receptors for hormones, viruses and bacterial toxins, but also as mediators in cell differentiation, proliferation, oncogenesis, immunity, and so on. For example, specific recognitions of sialyl-oligosaccharides are involved in the initial step of invasion of a mammalian cell by influenza virus [6] or Trypanosoma cruzi [7]. The sialyl Lewis X carbohydrate epitope, found on neutrophils, monocytes, and tumor cells, has been identified [8-10] as the ligand for selectins, a family of cell adhesion receptors that are implicated in the leukocyte traffic or extravasation to sites of inflammation, platelet adhesion, and probably tumor metastasis [11]. Various biological functions of oligo-and polysialyl glycoconjugates, such as ganglioside GQlb [12] and polysialoglycoproteins [13,14], have also been demonstrated.
