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

		+			=			+
	UDP-alpha-D-glucuronate	+		[protein]-3-O-(beta-D-galactosyl-(1->3)-beta-D-galactosyl-(1->4)-beta-D-xylosyl)-L-serine	=		UDP	+		[protein]-3-O-(beta-D-GlcA-(1->3)-beta-D-Gal-(1->3)-beta-D-Gal-(1->4)-beta-D-Xyl)-L-serine