Accepted name: galactosylxylosylprotein 3-β-galactosyltransferase
Reaction: UDP-α-D-galactose + [protein]-3-O-(β-D-galactosyl-(1→4)-β-D-xylosyl)-L-serine = UDP + [protein]-3-O-(β-D-galactosyl-(1→3)-β-D-galactosyl-(1→4)-β-D-xylosyl)-L-serine
Other name(s): galactosyltransferase II; uridine diphosphogalactose-galactosylxylose galactosyltransferase; UDP-galactose:4-β-D-galactosyl-O-β-D-xylosylprotein 3-β-D-galactosyltransferase; UDP-α-D-galactose:4-β-D-galactosyl-O-β-D-xylosylprotein 3-β-D-galactosyltransferase
Systematic name: UDP-α-D-galactose:[protein]-3-O-(β-D-galactosyl-(1→4)-β-D-xylosyl)-L-serine (configuration-inverting)
Comments: Involved in the biosynthesis of the linkage region of glycosaminoglycan chains as part of proteoglycan biosynthesis (chondroitin, dermatan and heparan sulfates). Requires Mn2+.
1.  Robinson, J.A. and Robinson, H.C. Initiation of chondroitin sulphate synthesis by β-D-galactosides. Substrates for galactosyltransferase II. Biochem. J. 227 (1985) 805–814. [PMID: 3924029]
2.  Schwartz, N.B. and Roden, L. Biosynthesis of chondroitin sulfate. Solubilization of chondroitin sulfate glycosyltransferases and partial purification of uridine diphosphate-D-galactose:D-xylose galactosyltransferase. J. Biol. Chem. 250 (1975) 5200–5207. [PMID: 1150655]
3.  Bai, X., Zhou, D., Brown, J.R., Crawford, B.E., Hennet, T. and Esko, J.D. Biosynthesis of the linkage region of glycosaminoglycans: cloning and activity of galactosyltransferase II, the sixth member of the β1,3-galactosyltransferase family (β3GalT6). J. Biol. Chem. 276 (2001) 48189–48195. [PMID: 11551958]
[EC created 1984, modified 2002]