Characterization of the oligosaccharide component of microsomal β-glucuronidase from rat liver

Abstract

The oligosaccharides of microsomal β-glucuronidase were analysed by gel permeation and weak anion exchange chromatography following hydrazine release. N-linked glycans, constituted 80% of the total glycan pool and were mainly of the tri- and biantennary complex type with or without core and arm fucose. The major oligosaccharide, that comprised 30.6% of all the species analysed, was structurally identified by reagent array analysis method and found to be a triantennary complex structure, Galβ1,4GlcNAcβ1,2Manα1,6(3)(Galβ1,4GlcNAcβ1,4(Galβ1,4GlcNAcβ1,2) Manα1,3(6))Manβ1,4GlcNAcβ1,4 GlcNAc. O-Linked glycans comprised 20% of the total glycan pool, the major species being Galβ1,3GalNAc. All of the N- and O-linked glycans were charged. Most of the negative charge was due to sialic acid (85.0%) with the remainder being phosphate present as phosphomonoesters (7.3%) and phosphodiesters (5%). This is the first report of O-linked carbohydrate chains in microsomal β-glucuronidase. The presence of O-linked glycans and branched N-linked glycans in a microsomal enzyme, in relation to the current view of glycosyltransferase compartmentalization in the Golgi is discussed.