Reaction catalyzed by beta-galactoside alpha-2,3-sialyltransferase (2.4.3.4)

		+			=			+
	CMP	+		3-O-[alpha-Neu5Ac-(2->3)-beta-D-Gal-(1->3)-alpha-D-GalNAc]-L-tyrosyl-[protein]	=		CMP-N-acetyl-beta-neuraminate	+		3-O-[beta-D-Gal-(1->3)-alpha-D-GalNAc]-L-tyrosyl-[protein]