P-hexosaminidase transport in normal and I-cell fibroblasts

The carboxylic ionophore, monensin, blocks the migration of glycoprotein-containing vesicles from the Golgi region to the plasma membrane in fibroblasts resulting in an accumulation of secretory products in the Golgi cisternae. Treatment of cultured I-cell fibroblasts with monensin (0.5,UM) decreased the abnormal excretion of f-hexosaminidase to 40% of untreated cultures within 15 min. A corresponding intracellular accumulation of the enzyme to >200% of untreated cultures by 24 h was also observed. A small intracellular accumulation and slightly enhanced excretion of f3-hexosaminidase occurred in treated normal fibroblast cultures. The intraand extra-cellular distribution of newly synthesized f-hexosaminidase in both normal and I-cell cultures converged during monensin treatment. fJ-Hexosaminidase isoenzymes excreted by both monensin-treated normal and I-cell fibroblasts were electrophoretically indistinguishable from the four bands characteristic of I-cell intracellular fJ-hexosaminidase. The excreted enzyme from both cultures was found to be a lowor no-uptake form. This form of f)-hexosaminidase may have been excreted from a secondary route preceding the site of the monensin effect. The similar findings in monensin-treated normal and I-cell cultures suggest that the subcellular site of the biochemical defect in I-cell disease is at a location after the site of the monensin effect iLe. late in the Golgi region or at a post-Golgi-region location.