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Intracellular Transport of Acid α-Glucosidase in Human Fibroblasts: Evidencefor Involvement of Phosphomannosyl Receptor-Independent System1
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1988
Year
Protein SecretionGlycobiologyCellular PhysiologyMembrane TransportAutophagyPhosphomannosyl ReceptorAcid Alpha-glucosidaseProteomicsSecretory PathwayGlycosylationPhosphomannosyl Receptor-independent System1BiochemistryProtein TransportCell BiologyAcid α-GlucosidaseProtein PhosphorylationSignal TransductionIntracellular TransportNatural SciencesPhysiologyIntracellular TraffickingCellular BiochemistryMedicine
Intracellular transport of two lysosomal enzymes, acid alpha-glucosidase and beta-hexosaminidase, was analyzed in human fibroblasts. The precursors of beta-hexosaminidase in normal fibroblasts were released from the membrane fraction by treatment with mannose 6-phosphate, but the precursor of alpha-glucosidase was not. Percoll density gradient centrifugation revealed a normal amount of acid alpha-glucosidase activity in heavy lysosomes in I-cell disease fibroblasts despite impaired maturation and defective phosphorylation, and beta-hexosaminidase activity was markedly reduced in lysosomes. It was concluded that the membrane-bound precursor of acid alpha-glucosidase is transported to lysosomes by a phosphomannosyl receptor-independent system although the enzyme lacks the recognition marker for the phosphomannosyl receptor and processing of an intermediate form to mature forms does not occur in this disease.