α-L-Iduronidase in normal and mucopolysaccharidosis-type-I human skin fibroblasts

α-L-Iduronidase synthesis and maturation were analysed in fibroblasts from normal controls and from α-L-iduronidase-deficient mucopolysaccharidosis-type-I (MPS-I) patients. Fibroblasts were radiolabelled with [³H]leucine and α-L-iduronidase was isolated from cell lysates or culture medium by monoclonal-antibody affinity chromatography. Pulse-chase labelling of normal control fibroblasts showed that α-L-iduronidase was synthesized as an 81 kDa precursor and processed within 24 h via intermediates of 76 kDa and 70 kDa to a 69 kDa species. The incorporation of radiolabel into α-L-iduronidase in fibroblasts from three of four MPS-I patients was at levels that were either very low or undetectable. Fibroblasts from one MPS-I patient, however, exhibited levels of incorporation of radiolabelled amino acid into α-L-iduronidase similar to those shown by normal control fibroblasts, despite having undetectable α-L-iduronidase enzyme activity. The maturation of α-L-iduronidase in fibroblasts from this patient was delayed compared with normal controls and showed accumulation of the 76 kDa intermediate, as well as the major 69 kDa, form of the enzyme.