Glycosphingolipid β-Galactosidases

Abstract

Abstract Hepatic β-galactosidases were studied in tissues of five patients with Gm1-gangliosidosis. Activities of 4-methylumbelliferyl, lactosylceramide, Gm1-ganglioside and asialo Gm1-ganglioside β-galactosidases were deficient in livers of patients. In contrast, activities of galactosylceramide β-galactosidase were generally higher than in control tissues. The peak of residual activities of 4-methylumbelliferyl β-galactosidase had an abnormal isoelectric point of 4.6 to 4.7 by electrofocusing. In a late onset type II patient, the activity peaks of galactosylceramide and lactosylceramide β-galactosidases had isoelectric points similar to those in normal control liver tissues, while two patients with type I disease showed highly abnormal electrofocusing patterns of these enzymes. The peaks were shifted substantially toward lower pH. These findings indicate that, in addition to the frank deficiency of some sphingolipid β-galactosidases, there are more subtle and extensive abnormalities of β-galactosidases in Gm1-gangliosidosis. The difference in the electrofocusing patterns of galactosylceramide and lactosylceramide β-galactosidases suggests another enzymatic criterion which might possibly differentiate the phenotypically defined two types of the disease.