Multiple abnormalities of ectoglycosyltransferases in cultured fibroblasts from patients with mucolipidosis II: Possible indication for abnormal plasma membrane glycoproteins

Ectoglycosyltransferase activities were measured in cultured normal and mucolipidosis II fibroblasts using endogenous glycoproteins and glycolipids and whole cells. Nucleotide pyrophosphatase, known to interfere with glycosyltransferases, was completely inhibited with 6 mM 5’ AMP. Since preliminary experiments have shown multiple abnormalities of ectoglycosyltransferases in mucolipidosis II fibroblasts (Di Donato, unpublished results), galactosyl (Gal)- and Aiacetylglucosaminyl (GluNac)- transferase were studied in further detail in confluent and non- confluent cultures of normal and patient fibroblasts. Activities of both transferases on glycoproteins were higher in nonconfluent cultures. A 50% reduced activity of Gal-transferase was measured in confluent mucolipidosis II cultures and of GluNac- transferase in nonconfluent mucolipidosis II cultures towards incorporation of sugar precursors into glycoprotein. Substrate saturation kinetics of both transferases in mucolipidosis II fibroblasts revealed an abnormal K_m for Gal incorporation into endogenous glycoproteins. Glycosylation of glycolipids in mucolipidosis fibroblasts was normal. Speculation: The finding of multiple abnormalities of ectoglycosyltransfer-ases in mucolipidosis fibroblasts is compatible with an abnormal composition of the cell membrane glycoproteins. We speculate that there could be a link between these results and the abnormal glycoproteins recognition marker of lysosomal enzymes, both resulting from a common defect in glycosylation.