Cultured human skin fibroblasts from control persons and from patients with the generalized and late-onset forms of Pompe's disease were labelled with radioactive leucine and the incorporation of radioactivity into acid α-glucosidase and cathepsin D was analysed by immunoprecipitation, gel electrophoresis and fluorography. When the labelling was carried out for 6–12 h in the presence of NH4Cl, the labelling of secreted α-glucosidase relative to that of secreted cathepsin D in fibroblasts from patients with the late-onset form of Pompe's disease was < 15% of that in fibroblasts from control persons. However, when the fibroblasts were labelled for < 1 h, the relative rate of incorporation of radioactivity into acid α-glucosidase was rather similar in the two types of fibroblasts. In fibroblasts from patients with the generalized form of Pompe's disease no incorporation of radioactivity into acid α-glucosidase could be detected.
