title: Infantile sialic acid storage disease: the fate of biosynthetically labeled N-acetyl-(3H)-neuraminic acid in cultured human fibroblasts.
abstract: N-acetyl-(3H)-mannosamine[(3H)-ManNAc] was used as a precursor for the metabolic labeling of N-acetyl-(3H)-neuraminic acid [(3H)-NANA] in cultured fibroblasts of a patient with infantile sialic acid storage disease (ISSD). The metabolic fate of free and bound (3H)-NANA, isolated by high-performance liquid chromatography, was followed under pulse-chase labeling conditions. Nonsaturable accumulation of free (3H)-NANA was observed in ISSD, while the metabolic flux from (3H)-ManNAc to NANA-glycoconjugates was unaffected. Accumulated free (3H)-NANA could not effectively be chased from ISSD cells although N-acetyl-(3H)-hexosamines [(3H)-HexNAc] were appearing in the chase medium. These metabolites could arise from (3H)-NANA bound to glycoconjugates which were cleaved at normal rates in ISSD. The finding that free (3H)-NANA was markedly increased relative to its major products (3H)-HexNAc is suggestive for an impaired degradation and reutilization of (3H)-NANA due to trapping in a metabolically unaccessible pool. In titration experiments with digitonin a clear-cut increase in the latency of labeled NANA relative to a cytoplasmic marker enzyme was evident in ISSD. The release of (3H)-NANA, however, followed closely the digitonin-induced release of the lysosomal enzyme beta-hexosaminidase. This is suggestive for a lysosomal location of the stored material.
mesh_terms: D001692:Biological Transport; D002239:Carbohydrate Metabolism, Inborn Errors / Q000378:metabolism*; D002451:Cell Compartmentation; D002478:Cells, Cultured; D005347:Fibroblasts / Q000378:metabolism; D006596:Hexosaminidases / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D012794:Sialic Acids / Q000378:metabolism*; D001619:beta-N-Acetylhexosaminidases
chemical_list: D012794:Sialic Acids; D007770:L-Lactate Dehydrogenase; D006596:Hexosaminidases; D001619:beta-N-Acetylhexosaminidases