Disaccharide units from complex carbohydrates of animals

Glycoprotein metabolism in normal and beta-mannosidase-deficient cultured goat skin fibroblasts

Cultured skin fibroblasts established from goats affected with beta-mannosidosis, an inherited neurovisceral storage disorder, showed an absence of lysosomal beta-mannosidase activity and the corresponding accumulation of a trisaccharide (TS) with the structure Man beta (1----4)GlcNAc beta (1----4)GlcNAc (0.4 mumol/g) and lesser amounts (0.15 mumol/g) of a Man beta (1----4)GlcNAc disaccharide (DS). By using purified storage TS isolated from fibroblasts metabolically labelled with [3H]GlcN, no conversion of TS into DS could be demonstrated in homogenates of affected cells at either lysosomal pH (4.4) or cytosolic pH (6.1), or in the culture medium (pH 7.0) of affected cells. Both TS and DS were secreted into the culture medium by affected fibroblasts. When affected fibroblasts were treated with tunicamycin before labelling with [3H]GlcN, the accumulation of both labelled TS and DS was completely inhibited. Treatment of both affected and normal goat fibroblasts with swainsonine resulted in the inhibition of lysosomal alpha-mannosidase activity and in the accumulation of the same labelled oligosaccharides in both. The major storage pentasaccharide from both normal and affected swainsonine-treated fibroblasts was sensitive to digestion with alpha-mannosidase and endo-beta-N-acetylhexosaminidase D, suggesting a branched mannose structure and a chitobiose core. In the absence of evidence for the existence of unusual N-linked glycoprotein-associated chitotriose oligosaccharide structures in affected goat fibroblasts, it must be concluded that degradative pathways for N-linked oligosaccharides are similar in both normal and affected goat fibroblasts, and that these pathways differ from catabolic pathways in human fibroblasts.

Substrate specificity and other properties of the beta-D-galactosidase from Aspergillus niger

beta-D-Galactosidase from Aspergillus niger was purified by conventional techniques, including the repeated use of chromatography on hydroxylapatite. The final preparation represented a 112-fold purification, with a 22% yield. The specific activity of the purified enzyme was 72 mumol of D-galactose released/min/mg of protein, using p-nitrophenyl beta-D-galactopyranoside as the substrate. The substrate specificity of the enzyme was studied by using saccharides having structural linkages similar to those found in naturally occurring glycoconjugates. At substrate concentrations of 5mM, the beta-D-galactosidase efficiently hydrolyzed beta-Gal-1 leads to OC6H4NO2-p, beta-Gal-(1 leads to 3)-Gal, beta-Gal-(1 leads to 3)-beta-Gal-1 leads to OC6H4NO2-p, and beta-Gal-(1 leads to 3)-alpha-Gal-1 leads to OC6H4NO2-p, at rates of 63, 53, 65, and 29 mumol/min/mg of protein, respectively. Slower hydrolysis was observed for beta-Gal-(1 leads to 4)-beta-Glc, beta-Gal-(1 leads to 4)-beta-GlcNAc-1 leads to OC6H4NO2-p, and beta-Gal-(1 leads to 6)-beta-GlcNAc-1 leads to OC6H4NO2-p, with rates of 10, 13 and 9 mumol/min/mg of protein, respectively. Poorly hydrolyzed, at rates 1/300th of that of beta-Gal-1 leads to OC6H4NO2-p, were synthetic substrates having D-galactose attached beta-(1 leads to 3)- to either GalNAc or GlcNAc. The Km value for beta-D-galactosidase with beta-Gal-(1 leads to 4)-beta-GlNAc-1 leads to OC6H4NO2-p was approximately 20 times that with beta-Gal-1 leads to OC6H4NO2-p. The beta-D-galactosidase of A. niger has a molecular weight of 300,000, as demonstrated by gel-filtration chromatography. Sodium dodecyl sulfate-poly(acrylamide)-gel electrophoresis indicated a single subunit having a molecular weight of 130,000.

A novel neutral oligosaccharide chain found in polysialoglycoproteins isolated from Pacific salmon eggs. Structural studies by secondary ion mass spectrometry, proton nuclear magnetic resonance spectroscopy, and chemical methods

A novel carbohydrate chain possessing a hitherto unknown disaccharide unit, alpha-L-Fuc leads to D-GalNAc, has been isolated from salmon egg polysialoglycoproteins on alkali-borohydride treatment. Salmon egg polysialoglycoproteins contain O-glycosidically linked neutral pentasaccharide chains in addition to a number of oligosialosyl group containing sugar chains. Composition analysis of the neutral pentasaccharide gave fucose, galactose, 2-acetamido-2-deoxygalactose, and 2-acetamido-2-deoxygalactitol in a molar ratio of 1:2:1:1. The structure was determined to be alpha-L-Fuc(1 leads to 3)-beta-D-GalNAc-(1 leads to 3)-beta-D-Gal(1 leads to 4)-beta-D-Gal(1 leads to 3)-D-GalNAcol by the following three major procedures: First, the sequential order of the constitutional monosaccharides was determined by secondary ion mass spectrometry before and after permethylation. Second, linkages were established by methylation analysis and Smith degradation and hydrazinolysis-nitrous deamination studies. Third, anomeric configuration of the glycosidic linkages involved was deduced from 270-MHz proton nuclear magnetic resonance spectroscopy.

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.