Fibroblasts from patients with mannosidosis, cultured in medium supplemented with fetal calf serum from which acidic α-mannosidase (α-D-mannoside mannohydrolase, E.C.126.96.36.199) has been removed, secreted a normal amount of apparently unaffected acidic α-mannosidase into fetal calf serum-free medium. Both the intracellular and extracellular acidic α-mannosidase activities were completely precipitated by antiserum to placenta α-mannosidase B. In contrast to the heat-lability of the intracellular acidic α-mannosidase and its low affinity for artificial mannoside substrate, the extracellular enzyme inhibited both normal thermostability and normal kinetics. Mixing experiments with the intracellular enzymes suggested that the decreased activity in the patients' fibroblasts is not the effect of an inhibitor or absence of an activator. However, incubation of the mannosidosis extracellular enzyme with either normal or patient cell lysate resulted in a partial loss of activity, whereas an additive value was observed with the normal extracellular enzyme. In contrast to normal culture medium, the medium from mannosidosis cell culture was unable to enhance the rate of reduction of intracellular radioactivity in mucolipidosis type II fibroblasts precultured in the presence of radiolabeled mannose. These findings suggest that the defect in mannosidosis is expressed only after the enzyme has been delivered to lysosomes and presumably undergone some form of processing there.
|Original language||English (US)|
|Number of pages||12|
|Journal||American Journal of Human Genetics|
|State||Published - Apr 9 1982|
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