Purification and characterization of alpha-N-acetylgalactosaminidases I and II from the starfish Asterina amurensis.

Two alpha-N-acetylgalactosaminidases, alpha-N-acetylgalactosaminidase (alpha-GalNAcase) I and II, were purified from the digestive organ of starfish. Purified alpha-GalNAcase I and II gave nearly single protein bands on SDS-polyacrylamide gel electrophoresis, individually. Even the final preparation of alpha-GalNAcase I contained alpha-galactosidase activity, while alpha-GalNAcase II was almost free from that activity with p-nitrophenyl and 4-methylumbelliferyl alpha-N-acetylgalactosaminides as substrates. alpha-GalNAcase I and II both hydrolyzed terminal alpha-N-acetylgalactosaminyl linkages of the natural compounds investigated: Forssman hapten glycolipid, blood group A active oligosaccharide and GalNAc-alpha1-O-serine. On the other hand, oligosaccharides, and glycolipid containing alpha-galactosyl terminals were hydrolyzed by alpha-GalNAcase I but not by alpha-GalNAcase II. The substrate specificities and other enzymatic properties of alpha-GalNAcase I were similar to those of human placental alpha-GalNAcase, but distinct from alpha-GalNAcase II.