β-galactosidase

β-ga·lac·to·si·dase (gə-lak″to-siґdās) [EC 3.2.1.23] any of a group of enzymes of the hydrolase class that catalyze the cleavage of terminal, β-linked, nonreducing galactose residues from a variety of substrates, including ganglioside GM₁, lactosylceramides, lactose, and various glycoproteins and oligosaccharides. See also lactase. The lysosomal (acid) isozyme catalyzes the hydrolysis of β-galactosides in gangliosides and keratan sulfate, and its catalytic activity with these substrates is differentially impaired in several autosomal recessive disorders caused by allelic mutations. In GM₁ gangliosidosis, activity toward ganglioside GM₁ is particularly decreased or absent, while in Morquio syndrome, type B, this activity is normal but activity toward keratan sulfate is decreased.