Ganglioside GM1 beta-galactosidase: studies in human liver and brain

A microcolumn assay for ganglioside GM₁ β-galactosidase (EC 3.2.1.23) has been developed using GM₁ tritiated exclusively in the terminal galactose residue. The reaction is stimulated up to 100-fold by anionic and cationic detergents; this stimulation is inhibited by neutral detergents. 4-Methylumbelliferyl β-d-galactopyranoside is hydrolyzed about seven times more rapidly than GM₁ in human brain (gray matter) and liver. Agarose gel filtration separated two forms of GM₁ β-galactosidase in both brain and liver. The major form (ganglioside GM₁ β-galactosidase A) had a molecular weight of 60–70 × 10³ and the minor form (ganglioside GM₁ β-galactosidase B) 600–800 × 10³. The liver and brain GM₁ β-galactosidases and 4-methylumbelliferyl β-galactosidase A cochromatographed on fractionation. The two forms of the enzyme in liver isolated by gel filtration corresponded to the two major forms found on starch gel electrophoresis and were converted to electrophoretically slower-moving forms after treatment with neuraminidase (EC 3.2.1.8, Cl. perfringens) suggesting that both are sialylated glycoproteins. The activity of GM₁ β-galactosidase in the brain and liver tissue of patients with GM₁ gangliosidosis Types I and II was less than 2% of control values. The mutation in each GM₁ gangliosidosis appears to result in a severe reduction of activity of two ganglioside GM₁ β-galactosidases.