A micro-radiochemical assay forα-1,4-glucosidase

An assay system for α-l,4-glucosidase (acid maltase) which is deficient in glycogen storage disease Type 2 (Pompe's disease) has been developed. The assay, which represents an improvement in sensitivity of at least 100-fold over the more conventional colorimetric methods is used to measure the enzyme activity in peripheral blood leucocytes, cultured amniotic cells and skin fibroblasts, has a total volume of 8 μl and uses (U- 14 C) maltose as the substrate, The product (U- 14 C) glucose is separated from the substrate by cellulose thin layer chromatography. The procedure allows the assay of acid maltase in cell extracts equivalent to about 2000–5000 cultured cells or 0.5-1.0 × 10 5 leucocytes isolated from 400 μl of whole blood. The assay has been used to measure the enzyme activity in fibroblasts and leucocytes derived from normal subjects, an affected patient and to assess the genotype of two foetuses suspected of being affected by Pompe's disease.