Metabolic correction of fucosidosis fibroblasts by human α‐L‐fucosidase

Human α‐L‐fucosidase, purified from placenta, was taken up from the culture medium by skin fibroblasts from patients with fucosidosis (α‐L‐fucosidase deficiency). The rate of uptake was low (uptake coefficient = 6 × 10⁻⁴ ml.mg⁻¹.h⁻¹). Intracellular α‐L‐fucosidase activity was directly proportional to enzyme in the medium up to an activity of at least 40 nmoles/min/ml. No evidence for saturation of specific cell‐surface receptors was seen. However, uptake was reduced by 75% by 1 mM mannose‐6‐phosphate and by 50% by 1 mM glucose‐6‐phosphate, suggesting that uptake may be mediated by a receptor recognising a phosphorylated sugar or an analagous compound. Enzyme taken up by the cells was most active in subcellular fractions enriched with lysosomes and had an isozyme pattern, by isoelectric focusing, identical to that of the original enzyme preparation. Fucosidosis fibroblasts were shown to accumulate low molecular‐weight, fucose‐containing compounds to a level several times greater than control cells. This stored material was eluted from Sephadex G‐25 as an asymmetrical peak with an elution volume of approximately twice the void volume of the column. Addition of placental α‐L‐fucosidase to the culture medium of fucosidosis fibroblasts prevented excessive accumulation of fucose‐containing material and accelerated the breakdown of material accumulated prior to enzyme uptake.