THE STRUCTURE OF THE ASPARAGINE-LINKED SUGAR CHAINS OF BOVINE BRAIN RIBONUCLEASE

The asparagine-linked sugar chains of bovine brain ribonuclease were quantitatively released as oligosaccharides from the polypeptide backbone by hydrazinolysis. After N-acetylation, they were converted into radioactively-labeled oligosaccharides by NaB3H4 reduction. The radioactive oligosaccharide mixture was fractionated by ion-exchange chromatography, and the acidic oligosaccharides were converted into neutral oligosaccharides by sialidase digestion. The neutral oligosaccharides were then fractionated by Bio-Gel P-4 column chromatography. Structural studies of each oligosaccharide by sequential exoglycosidase digestion in combination with methylation analysis revealed that bovine brain ribonuclease showed extensive heterogeneity. It contains bi- and tri-antennary, complex-type oligosaccharides having α-d-Manp-(1→3)-[α-d-Manp-(1→6)]-β-d-Manp-(1→4)-β-d-GlcpNAc-(1→4)- [α-l-Fucp-(1→6)]-d-GlcNAc as their common core. Four different outside oligosaccharide chains, i.e., β-d-Galp-(1→4)-β-d-GlcpNAc-(1→, α-Neu5Ac-(2→6)-β-d-Galp-(1→4)-β-d-GlcpNAc-(1→, α-Neu5Ac-(2→3)-β-d-Galp-(1→4)-β-d-GlcpNAc-(1→, and α-d-Galp-(1→3)-β-d-Galp-(1→4)-β-d-GlcpNAc-(1→, were found. The preferential distribution of the α-d-Galp-(1→3)-gb-d-Galp-(1→4)-β-d-GlcpNAc group on the α-d-Manp-(1→6) arm is a characteristic feature of the sugar chains of this enzyme. © 1990.