Reaction catalyzed by polypeptide N-acetylgalactosaminyltransferase (2.4.1.41)

		+			=			+
	UDP-N-acetyl-alpha-D-galactosamine	+		GT[GalNAc]TPSPVPTTSTTSAP	=		UDP	+		GT[GalNAc]TPSPVPTTS[GalNAc]T[GalNAc]TSAP