Leucocyte alpha-1,4- and alpha-1,6-glucosidase activities towards oligosaccharides in late onset glycogenosis type II

We describe the partial characterization and some properties of leucocyte alpha-glucosidase towards disaccharides with the alpha-1,4 (maltose) and alpha-1,6-glucosidic linkage (isomaltose) and tetrasaccharides with the alpha-1,4 (maltotetraose) and alpha-1,6-glucosidic linkage (tetrasaccharide, Glc alpha 1----6Glc alpha 1----4Glc alpha 1----4Glc, which was isolated from the urine of a patient with glycogenosis type II). Leucocyte alpha-glucosidase showed optimal activity towards all four oligosaccharides under two conditions, acidic (pH 4.0-4.5) and neutral (pH 6.0-6.5) regions. Our comparative studies on Enzyme kinetics showed that leucocyte alpha-glucosidase was able to hydrolyze both the 1----4 isomers and the 1---6 isomers at acidic and neutral pH. Acid alpha-glucosidase could hydrolyze maltose about 10 times faster than isomaltose, and maltotetraose about 5 times faster than tetrasaccharide isolated from urine. In leucocytes of the patient with late onset glycogenosis type II, acid alpha-glucosidase activities towards maltose, isomaltose, maltotetraose and tetrasaccharide isolated from urine showed 75.3%, 67.4%, 76.5% and 41.4% of normal control values, respectively. Neutral alpha-glucosidase activities towards these four oligosaccharides were normal. Tetrasaccharide with alpha-1,6-glucosidic linkage might be accumulated by the impaired hydrolysis in the circulation as well as the leakage of undegraded glycogen to the circulation from the affected muscle.