During the course of a study to elucidate the role ofmodification of the common polysaccharide-protein linkagestructure, GlcAb1–3Galb1–3Galb1–4Xylb1-O-Ser, inbiosynthetic sorting mechanisms of the different sulfatedglycosaminoglycan chains, a novel N-acetylgalactosamine(GalNAc) transferase was discovered in fetalbovine serum. The enzyme catalyzed the transfer of[3H]GalNAc from UDP-[3H]GalNAc to linkage tetrasaccharideand hexasaccharide serines synthesized chemicallyand to various regular oligosaccharides containingterminal D-glucuronic acid (GlcA), which were preparedfrom chondroitin and chondroitin sulfate using testicularhyaluronidase digestion. The labeled products obtainedwith the linkage tetra- and hexasaccharideserines and with the tetrasaccharide (GlcAb1–3GalNAc)2were resistant to digestion with chondroitinase AC-IIand b-N-acetylhexosaminidase but sensitive to a-Nacetylgalactosaminidasedigestion, indicating that theenzyme is an a-N-acetylgalactosaminyltransferase. Thisfinding is in contrast to that of Rohrmann et al. (Rohrmann,K., Niemann, R., and Buddecke, E. (1985) Eur. J.Biochem., 148, 463–469), who reported that a correspondingproduct was susceptible to digestion with b-Nacetylhexosaminidase.The presence of a sulfate groupat C4 of the penultimate GalNAc or Gal units markedlyinhibited the transfer of GalNAc to the terminal GlcA,while a sulfate group at C6 of the GalNAc had little effecton the transfer. Moreover, a slight but significant transferof [3H]GalNAc was observed to an oligosaccharidecontaining terminal 2-O-sulfated GlcA as acceptor,whereas no incorporation was detected into oligosaccharidescontaining terminal unsaturated or 3-O-sulfatedGlcA units. These results suggest that this novelserum enzyme is a UDP-GalNAc:chondro-oligosaccharidea1–3- or 1–4-N-acetylgalactosaminyltransferase.
1995. Vol. 270, no 38, 22190-22195 p.