Human Brain Cerebroside β-Galactosidase: Deficiency of Transgalactosidic Activity in Krabbe's Disease

Abstract: Under experimental conditions optimal for the assay of D-galactosyl- N -acylsphingosine galactohydrolase (EC 3.2.1.46) activity, homog-enates of neurologically normal human brain tissue could transfer galactose from galactosyl ceramide (gal-cer), lactosyl ceramide (lac-cer), 4-methylumbelliferyl- β-galactoside (4-MU-gal), or p -nitrophenyl- β-galactoside (PNP-gal) to [1-¹⁴C]oleoyl sphingosine, but homogenates of brain tissue from patients with Krabbe's disease lacked this ability. The rate of hydrolysis of ganglioside G_M1 and to a lesser extent, of PNP-gal by homogenates of Krabbe's brain tissue was also decreased. Activity of PNP- β-galactosidase in normal brain tissue, like that of cerebroside β-galactosidase from the same source, was considerably more heat-stable than the activity of either 4-MU- β-galactosidase or the predominant G_M1β-D-galactosidase (EC 3.2.1.23). Lac-cer and G_M1, as well as 4-MU-gal and PNP-gal, were competitive inhibitors of human-brain cerebroside β-galactosidase. These findings confirm the ability of mammalian cerebroside β-galactosidase to catalyze a transgalactosylation reaction and provide additional information on the substrate specificity of human brain cerebroside β-galactosidase.