Purification and characterization of I-cell disease alpha-L-fucosidase.

The molecular defect responsible for I-cell disease and pseudo-Hurler polydystrophy is unknown but may result in an altered carbohydrate composition on the lysosomal hydrolases.This concept was investigated by purifying a-L-fucosidase to apparent homogeneity from normal and I-cell liver samples and pseudo-Hurler polydystrophy urine samples.Gas-liquid chromatographic analysis of the sugar residues on the purified a-L-fucosidase preparations revealed an increase in the quantity of mannose, galactose, glucose, N-acetylglucosamine, and sialic acid found on the I-cell and pseudo-Hurler polydystrophy enzymes when compared to the normal liver a-L-fucosidase.The a-L-fucosidase from normal liver was composed of a major subunit with a molecular weight of 51,000 and a minor subunit of molecular weight of 57,000, while the enzyme from pseudo-Hurler polydystrophy urine exhibited a minor subunit at M, = 51,000 and a major subunit at M, = 57,000.The heterogeneity of the isoelectric focusing profiles of the normal, I-cell, and pseudo-Hurler polydystrophy a-L-fucosidase was due in part to alterations in the sialic acid content of the enzyme.The purified Icell liver a-tfucosidase displayed normal binding properties to concanavalin A, while the pseudo-Hurler polydystrophy urine enzyme revealed an altered interaction with this lectin.Comparisons of apparent K,,, and pH optimum of the a-L-fucosidases revealed no significant differences between the normal and I-cell samples.Our results indicate that the biochemical features of Icell disease and pseudo-Hurler polydystrophy may result from an altered carbohydrate composition on these enzymes.Inherited lysosomal storage disorders generally result from the deficiency of a single lysosomal hydrolase activity (1).However, two related disorders, I-cell disease and pseudo-Hurler polydystrophy, are characterized in cultured fibroblasts by deficiencies of acid /3-D-galactosidase, a-L-fucosidase, and a-D-neuraminidase activities, partially reduced activities of N-acetyl-/3-D-hexosaminidase, /3-D-glucuronidase, a-L-iduronidase, arylsulfatase A, a-D-galactosidase, acid lipase, and a-D-mannosidase, and normal activity levels of acid phosphatase and /3-D-glucosidase (2-6).Studies of the media from