Human brain cerebroside beta-galactosidase: deficiency of transgalactosidic activity in Krabbe's disease

Under experimental conditions optimal for the assay of D-galactosyl-N-acylsphingosine galactohydrolase (EC 3.2.1.46) activity, homogenates of neurologically normal human brain tissue could transfer galactose from galactosyl ceramide (gal-cer), lactosyl ceramide (lac-cer), 4-methylumbelliferyl-beta-galactoside (4-MU-gal), or p-nitrophenyl-beta-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 GM1 and, to a lesser extent, of PNP-gal by homogenates of Krabbe's brain tissue was also decreased. Activity of PNP-beta-galactosidase in normal brain tissue, like that of cerebroside beta-galactosidase from the same source, was considerably more heat-stable than the activity of either 4-MU-beta-galactosidase or the predominant GM1 beta-D-galactosidase (EC 3.2.1.23). Lac-cer and GM1, as well as 4-MU-gal and PNP-gal, were competitive inhibitors of human-brain cerebroside beta-galactosidase. These findings confirm the ability of mammalian cerebroside beta-galactosidase to catalyze a transgalactosylation reaction and provide additional information on the substrate specificity of human brain cerebroside beta-galactosidase.