Glycosidase that has specific alpha-N-acetylgalactosaminidase activity. Cleavage of non-reducing alpha-(1->3)-N-acetylgalactosamine residues from human blood group A and AB mucin glycoproteins, Forssman hapten and blood group A lacto series glycolipids. Binds 1 NAD(+) per subunit. The NAD(+) cannot dissociate. Belongs to the Gfo/Idh/MocA family. Glycosyl hydrolase 109 subfamily.