The enzyme UDP-GalNAc:glycoprotein hormone N-acetyl-galactosaminyltransferase adds GalNAc to the oligosaccharide moiety of certain glycoprotein hormones such as lutropin and thyrotropin. This enzyme also recognizes certain motifs on the peptide chain and the Asn-linked olgiosaccharide moiety on the protein (Manzella et al, 1996).