Mannose-binding protein, deficiency

The receptor-binding of high-uptake forms of lysosomal enzymes to human diploid skin fibroblasts has been demonstrated directly by using a sensitive assay for the bound enzyme. a-L-Iduronidase-deficient cells were incubated with human urinary a-L-iduronidase and the cell-associated enzyme was assayed with 4-methylumbelliferyl a-L-idopyranosiduronic acid. D-Mannose 6-phosphate greatly accelerated the dissociation of the bound enzyme, and during uptake of a-L-iduronidase the receptors were regenerated every few minutes, even in the absence of protein synthesis. 

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