The structure of the O-glycosylically-linked oligosaccharide chains of LPG-I, a glycoprotein present in articular lubricating fraction of bovine synovial fluid.

Periodate oxidation of LPG-1 established that N-acetylneuraminic acid residues are linked preponderantly alpha-(2 leads to 3) to D-galactose residues. The resistance of 2-acetamido-2-deoxy-D-galactose residues to periodate oxidation suggests that they are linked at either O-3 or O-4 to D-galactose residues. After treatment of LPG-1 with alkaline sulfite, approximately 80% of 2-acetamido-2-deoxygalactose was recovered as the sulfonic acid derivative. The Gal leads to GalNAc disaccharide released from sialic-acid-free LPG-I by digestion with endo-2-acetamido-2-deoxy-alpha-D-galactosidase (which suggests an alpha-D-GalNAc leads to L-Ser or -L-Thr linkage) gave a high color-yield in the Morgan-Elson reaction, indicating that 2-acetamido-2-deoxy-D-galactose residues are linked at C-3 to D-galactose residues. The migration of the released Gal-GalNAc disaccharide was the same as that of a standard sample of O-beta-D-galactosyl-(1 leads to 3)-2-acetamido-2-deoxy-D-galactose. Treatment of sialic acid-free LPG-I with Streptococcus pneumoniae beta-D-galactosidase, which hydrolyzes only galactosides linked beta-D-(1 leads to 4) gave no free D-galactose, whereas treatment of LPG-I with bovine testes beta-D-galactosidase released greater than 90% of D-galactose. These results provide evidence for beta-D-Galp-(1 leads to 3)-alpha-D-GalNAcp-(1 leads to 3) alpha-D-GalNAcp-(1 leads to 3)-L-Ser or -L-Thr and alpha-NeuAc-(2 leads to 3)-beta-D-Galp-(1 leads to 3)-L-Ser or -L-Thr structures. The sensitivity of the methods used and the recovery of constituents following treatment of LPG-I do not rule out the occurrence of small amounts of other tri- or tetra-saccharide chains.