Diagnosis of Pompe's disease using leukocyte preparations. Kinetic and immunological studies of 1,4-α-glucosidase in human fetal and adult tissues and cultured cells

Abstract

Kinetic and immunological studies of 1,4-α-glucosidase show that the distribution of acid, renal and neutral a-glucosidase at pH 4.0 and 6.5 is as follows: in liver and cultured fibroblasts and amniotic fluid cells the activity at pH 4.0 is mainly due to the acid enzyme. Even at pH 6.5, the activity is largely due to the residual activity of the acid enzyme. In kidney and leukocytes, however, the activity by acid enzyme at pH 4.0 represents only 30–60% of the total activity and the remaining activity is from renal enzyme. At pH 6.5, the activity is almost exclusively of renal enzyme. Renal a-glucosidase has a higher affinity for maltose ( K m , 0.8 mmol/l) than acid enzyme, however; for glycogen acid enzyme shows the highest affinity (20.7 g/l). There is no significant difference in the kinetic characteristics of α-glucosidase between fetal and adult tissues. In kidney, however, a relative increase in renal enzyme to acid enzyme with age is found, i.e. in fetal kidney the α-glucosidase activity at pH 4.0 is more than twice that at pH 6.5, whereas in adult kidney, the activity ratio at pH 4.0–6.5 is approximately 1. Antibodies for human liver acid a-glucosidase decrease the α-glucosidase activity in normal leukocytes by 22–75% at pH 4.0 (0.54–3.8 nmol/min per mg protein). The decrease is significantly lower in patients with Pompe's disease (0–0.11 nmol/min per mg protein) as well as in their parents and some siblings (0.15–0.70).