Neuraminic acid occurrence

Keratan sulfate consists of the disaccharide, iV-acetyl-lactosamine, linked /3-(1 3) to the D-galactopyranose residue of the next iV-acetyl-lactosamine unit. Keratan sulfate is the most heterogeneous of the glycosaminoglycans, with variable sulfate content linked to C-4 or C-6 of the D-galactop)Tanose residue in lactosamine, and small amounts of L-fucose (6-deoxy-L-galactose), D-mannose, and iV-acetyl-neuraminic acid residues [93] (also see Sects. 10.2 and O 14 on the occurrence of iV-acetyl-D-neuraminic acid and L-fucose in other systems). Keratan sulfate is found in the cornea, on the surfaces of erythrocytes, in cartilage, and in bone. 

The name sialic acid" has been given to the several nonulosaminic acids isolated from the submaxillary mucoproteins, although the chemical composition of these varies with the species source. Svennerholm has proposed that the name sialic acid be restricted to the basic structure common to all these various sialic acids thus ovine sialic acid" would be designated Af-acetylsialic acid. However since this basal component, here termed sialic acid, is identical with neuraminic acid, it would seem more appropriate to adopt the name neuraminic acid for the parent add and to retain the name sialic acid to denote the various mono- and di-acyl neuraminic acids of natural occurrence in mucoproteins, regardless of their source. This is the convention which has been used in referring to the various nonulosaminic acids in Table I and thoughout this article. ... 

Examination of the occurrence of neuraminic acid moieties in glycoproteins from pig submandibular and rat sublingual glands indicates that one in four neuraminic acid residues in the pig glycoprotein occurs as an a-iV-acylneur-aminyl-(2 8)-7V-acylneuraminyl unit. The disaccharide is absent in the corresponding rat glycoprotein. 

Kanamori, A., Inoue, S., Iwasaki, M., Kitajima, K., Kawai, G., Yokoyama, S., and Inoue, Y, 1990, Deaminated neuraminic acid rich glycoprotein of rainbow trout egg vitelline envelope Occurrence of a novel a-2,8-linked oligo (deaminated neuraminic acid) structure in O-linked glycan chains, J. Biol. Chem. 265 21811-21819. 

---