Reaction catalyzed by xylosyl alpha-1,3-xylosyltransferase (2.4.2.62)

		+		[protein with EGF-like domain]-3-O-[alpha-D-xylosyl-(1->3)-beta-D-glucosyl]-L-serine	=			+		[protein with EGF-like domain]-3-O-[alpha-D-xylosyl-(1->3)-alpha-D-xylosyl-(1->3)-beta-D-glucosyl]-L-serine
	UDP-alpha-D-xylose	+		[protein with EGF-like domain]-3-O-[alpha-D-xylosyl-(1->3)-beta-D-glucosyl]-L-serine	=		UDP	+		[protein with EGF-like domain]-3-O-[alpha-D-xylosyl-(1->3)-alpha-D-xylosyl-(1->3)-beta-D-glucosyl]-L-serine