Reaction catalyzed by galactosylgalactosylxylosylprotein 3-beta-glucuronosyltransferase (2.4.1.135)

		+			=			+
	UDP-galacturonic acid	+		Galbeta(1-3)Gal	=		Galbeta(1-3)Galbeta(1-3)Gal	+		UDP