Glucocerebrosidase, a lysosomal enzyme that does not undergo oligosaccharide phosphorylation

Labelling of cultured human skin fibroblasts from either control subjects or patients with mucolipidosis II (I-cell disease) with [32P]phosphate resulted in tight association of phosphate with immunoprecipitated glucocerebrosidase, a membrane-associated lysosomal enzyme. Endoglycosidase F digestion of the immunoprecipitated glucocerebrosidase did not release labelled phosphate, suggesting that the phosphate was not associated with the oligosaccharide moiety of this glycoprotein. Purification of the enzyme from cells labelled with [32P]phosphate and [35S]methionine by an immunoaffinity chromatography procedure, which included a washing step with detergent, resulted in complete separation of the phosphate label from the peak of glucocerebrosidase activity and methionine labelling. We conclude that oligosaccharide phosphorylation, which is essential for transport of soluble lysosomal enzymes to the lysosomes in fibroblasts, does not occur in glucocerebrosidase.