Oligosaccharides in Lysosomal Enzymes

Abstract

The distribution of the different types of oligosaccharides in cathepsin D and in β-hexosaminidase syn- thesized in cultured human fibroblasts was studied by using endo-β-N-acetylglucosaminidase H as a probe for high-mannose oligosaccharides. The enzymes were specifically labelled in the protein or the carbohydrate moiety. In both enzymes, resistant and cleavable oligosaccharides were found. The resistant oligosaccharides prevailed the secreted enzymes. Precursor molecules of cathepsin D contained two oligosaccharide side chains. Multiple forms of the precursor are synthesized with both, one or none of two oligosaccharides sensitive to the action of the endo-β-N-acetylglucosaminidase H. In fibroblasts unable to phosphorylate lysosomal enzymes (mucolipidosis 11) the excessively secreted lysosomal enzymes contained predominantly oligosaccharides resistant to endo-β-N-acetylglucosaminidase H.