Figure 7.

Enzymatic characterization of the mutant GlcNAc-phosphotransferase. Normal human skin fibroblasts (Wt); and skin fibroblasts from patients with classical MLIII (GM2425) and variant MLIII (GM3391); and patient VI:8 (pedigree 1), patient II:3 (pedigree 3), were cultured and a solubilized membrane fraction prepared as described in Methods. GlcNAc-phosphotransferase was assayed using both the lysosomal enzyme uteroferrin and α-methylmannoside as acceptors and calculated as pMol GlcNAc-1-phosphate transferred per milligram of cell protein per hour. The data are expressed as a percentage of the activity observed in the wild-type cell line.