GM1 ganglioside beta-galactosidase. A. Purification and studies of the enzyme from human liver.

GMM1-ganglioside fi-galactosidase A (EC 3.2.1.23) has been purified 17,000-fold from human liver. The enzyme appeared as a single band of protein on polyacrylamide gel electrophoresis. Double immunodiffusion of rabbit anti-pgalactosidase A antiserum against either GM1 /3-galactosidase A or liver supematant gave a single precipitin band. The apparent molecular weight was 65,000 to 75,000 by gel filtration of the native enzyme and 72,000 by sodium dodecyl sulfate gel electrophoresis of the denatured, reduced, and carboxymethylated enzyme. The purified enzyme liberated D-galactose from synthetic chromogenic and fluorogenic P-Dgalactosides, as well as lactose, N-acetyllactosamine, and the glycoprotein asialofetuin. The same catalytic site(s) appeared to be responsible for the hydrolysis of GMI-ganglioside and 4-methylumbehiferyl-&r+galactopyranoside. The enzyme also cleaved B-D-fucoside and a-L-arabinoside linkages. Lactulose, galactosyl-hydroxylysine, galactosyl-hydroxylysyl peptides, galactocerebroside, lactosylceramide, and monogalactosyldiglyceride were very poor susbtrates. Anti-/3-galactosidase A antiserum quantitatively precipitated both /3-galactosidase A and /3-galactosidase B. Neutral P-glucosidase (“nonspecific” /3-galactosidase), galactocerebroside /3-galactosidase, and lactosylceramide @-galactosidase were not precipitated by anti-P-galactosidase A antiersum.