The effect of monensin on beta-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 muM) decreased the abnormal excretion of beta-hexosaminidase to 40% of untreated cultures within 15 min. A corresponding intracellular accumulation of the enzyme to greater than 200% of untreated cultured by 24 h was also observed. A small intracellular accumulation and slightly enhanced excretion of beta-hexosaminidase occurred in treated normal fibroblasts cultures. The intra- and extra-cellular distribution of newly synthesized beta-hexosaminidase in both monensin-treated normal and I-cell fibroblasts were electrophoretically indistinguishable from the four bands characteristic of I-cell intracellular beta-hexosaminidase. The excreted enzyme from both cultures was found to be a low- or no-uptake form. This form of beta-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 i.e. late in the Golgi region or at a post-Golgi-region location.
D000118:Acetylglucosaminidase / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002478:Cells, Cultured; D005110:Extracellular Space / Q000201:enzymology; D005347:Fibroblasts / Q000187:drug effects / Q000201:enzymology; D005663:Furans / Q000494:pharmacology*; D006596:Hexosaminidases / Q000378:metabolism*; D006801:Humans; D008360:Mannosephosphates / Q000494:pharmacology; D008985:Monensin / Q000494:pharmacology*; D009081:Mucolipidoses / Q000201:enzymology*; D013347:Subcellular Fractions / Q000201:enzymology
D005663:Furans; D008360:Mannosephosphates; D008985:Monensin; D006596:Hexosaminidases; D000118:Acetylglucosaminidase