The carbohydrate moieties of human urinary ribonuclease UL

Ribonuclease UL purified from pooled human urine contains approximately 20.7% of neutral sugar and 7.8% of aminosugar. All sugars were quantitatively released as oligosaccharides on hydrazinolysis. The oligosaccharides were converted to tritium-labeled oligosaccharides on reduction with NaB3H4. The radioactive oligosaccharide fraction was separated into a neutral and an acidic fraction on paper electrophoresis. All oligosaccharides in the acidic fraction could be converted to neutral oligosaccharides with the release of one sialic acid residue by sialidase digestion. Both fractions were shown to be mixtures of more than fourteen oligosaccharides by gel permeation chromatography. Structural studies on these oligosaccharides involving sequential exoglycosidase digestion in combination with methylation analysis revealed that ribonuclease UL contains sialylated and non-sialylated mono, bi-, tri-, and tetraantennary complex type sugar chains with N-acetyllactosamine outer chains, and tri- and tetraantennary complex type sugar chains with various numbers of Gal beta 1----4GlcNAc beta 1----3Gal beta 1----4GlcNAc beta 1----outer chains. An important finding was that all sialic acid residues in the acidic oligosaccharides only occur as the Sia alpha 2----6Gal beta 1----4GlcNAc beta 1----2Man alpha 1----3 group. Both fucosylated and non-fucosylated trimannosyl cores were found among the asparagine-linked sugar chains of ribonuclease UL.