Reaction catalyzed by protein xylosyltransferase (2.4.2.26)

		+		bikunin-derived aminoterminus homologous peptide	=			+		xylosyl-serine bikunin-derived aminoterminus homologous peptide
	UDP-D-xylose	+		bikunin-derived aminoterminus homologous peptide	=		UDP	+		xylosyl-serine bikunin-derived aminoterminus homologous peptide