Human a-L-fucosidase, purified from placenta, was taken up from the culture medium by skin fibroblasts from patients with fucosidosis (a-L-fucosidase deficiency). The rate of uptake was low (uptake coefficient = 6
x lo-* ml.mg-l.h-*). Intracellular a-L-fucosidase activity was directly proportional to enzyme in the medium up to an activity of a t 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 a n asymmetrical peak with a n elution volume of approximately twice the void volume of the column. Addition of placental a-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.
Fucosidosis is an inborn error of metabolism characterized biochemically by deficiency of a-L-fucosidase activity and intracellular accumulation of fucose-containing glycoproteins, glycolipids and oligosaccharides (Van Hoof and Hers, '68; Durant et al., '69; Turner e t al., '75a; Kousseff et al., '76). Several different fucose-containing compounds have been isolated from tissues of patients with this disorder. These include a glycosphingolipid with H-antigen specificity (Dawson and Spranger, '71), a branched dekasaccharide with Fuc (el-2) Gal termini and a small glycopeptide with the structure Fuc (al-6). GlcNac. Asn (Tsay et al., '76). A compound which is probably identical to this glycopeptide has been isolated from cultured skin fibroblasts derived from patients with fucosidosis (Tsay and Dawson, '75). Accumulation of this compound probably accounts, at least in part, for the abnormally high incorporation of tritiated fu-