Partial Characterization of Leucocyte α-Glucosidase in Late Onset Glycogenosis Type II

Abstract

We describe partial characterization and properties of leucocyte α-glucosidase from a patient with clinical features intermediate of juvenile and adult onset forms of glycogenosis type II. Acid and neutral α-glucosidase activities toward 4-methylumbelliferyl glucopyranoside as substrate were studied in total leucocytes, and separately in lymphocytes and granulocytes. Lymphocytes, which showed markedly reduced activities of acid α-glucosidase in the patient, are the most reliable peripheral blood cells for the diagnosis of glycogenosis type II. Moreover, the ratio of acid/neutral α-glucosidase activities, especially in lymphocytes, is a useful parameter for the diagnosis. In lymphocytes, the Km values of both acid and neutral α-glucosidases were essentially the same between the patient and normal controls; the Vmax value of acid α-glucosidase from the patient was markedly reduced, and the Vmax value of neutral α-glucosidase from the patient was reduced by 36% as compared with that from normal controls. Heat-inactivation experiments revealed that acid α-glucosidase activities of lymphocytes were relatively heatstable, while both acid and neutral α-glucosidases of granulocytes were heat-labile. No differences in these properties, however, could be detected between the patient and normal controls. © 1989, Tohoku University Medical Press. All rights reserved.