α‐L‐iduronidase deficiency in mucopolysaccharidosis type I against a radio‐labelled sulfated disaccharide substrate derived from dermatan sulfate

α-L-Iduronidase activity was assayed by incubation of a radiolabeled disaccharide, 0-(α-L-idopyranosyluronic acid)-(l 3)-2,5 anhydro-D-[I,3H]-talitol 4-sulfate (IdoA-anT4S) derived from dermatan sulfate, with homogenates of leucocytes, cultured amniotic cells and skin fibroblasts from normal individuals and patients affected with an α-L-iduronidase-deficiency disorder (mucopolysaccharidosis type I, MPS I), parents of such patients and patients affected with other mucopolysaccharidoses. The assay clearly distinguished affected homozygotes from normal controls, heterozygotes and other mucopolysaccharidosis types. Preliminary results show that fibroblast homogenates from patients with the MPS I Hurler phenotype were virtually unable to hydrolyse IdoA-anT4S, whereas fibroblast homogenates from a patient with a relatively mild (Scheie) phenotype exhibited a residual activity with Vmax value of 2.5 pmol/min/mg protein and an apparent Km of 21 /anol/1 compared to a range of 1020–2105 pmol/min/mg for Vmax and 12–35 /rniol/1 for Km for fibroblasts from normal controls.