MAMMALIAN ALPHA-ACETYLGALACTOSAMINIDASE . OCCURRENCE PARTIAL PURIFICATION AND ACTION ON LINKAGES IN SUBMAXILLARY MUCINS

α-Acetylgalactosaminidase, a lysosomal enzyme, is demonstrable in mammalian tissues, using phenyl-N-acetyl-α-galactosaminide as a substrate. The enzyme has been purified 300-fold from pig liver extracts and 700-fold from beef liver extracts, and is distinct from α- or β-acetylglucosaminidase. Pig liver contains at least eight isozymes of α-acetylgalactosaminidase and at least four of β-acetylglucosaminidase. For beef liver α-acetylgalactosaminidase, apparent specific activity decreases on dilution. This abnormality is most pronounced at higher temperatures and lower substrate concentrations. The purified α-acetylgalactosaminidase preparations catalyze release of N-acetylgalactosamine from desialized sheep and beef submaxillary mucins, but not from the untreated glycoproteins. Study of this action shows that most of the acetylgalactosamine residues in both glycoproteins are nonterminal (as already known for the sheep mucin), and that these residues are bound to the peptide core by α-glycosidic linkages. Results of similar experiments with purified β-acetylglucosaminidase suggest the presence of appreciable β-linked, nonterminal acetylglucosamine in beef submaxillary mucin. The purified α-acetylgalactosaminidase preparations also act on blood-group A substance from pig stomach. © 1969, American Chemical Society. All rights reserved.