title: Biosynthesis of polylactosaminoglycans. Novikoff ascites tumor cells contain two UDP-GlcNAc:beta-galactoside beta 1----6-N-acetylglucosaminyltransferase activities.
abstract: Novikoff ascites tumor cells contain a UDP-GlcNAc:beta-galactoside beta 1----6-N-acetylglucosaminyltransferase (beta 6-GlcNAc-transferase B) that acts on galactosides and N-acetylgalactosaminides in which the accepting sugar is beta 1----3 substituted by a Gal or GlcNAc residue. Characterization of enzyme products by 1H-NMR and methylation analysis indicates that an R beta 1----3(GlcNAc beta 1----6)Gal- branching point is formed such as occurs in blood-group-I-active substances. The enzyme does not show an absolute divalent cation requirement and 20 mM EDTA is not inhibitory. The activity is strongly inhibited by Triton X-100 at concentrations of greater than or equal to 0.2%. Competition studies suggest that a single enzyme acts on Gal beta 1----3Gal beta 1----4Glc, GlcNAc beta 1----3Gal beta 1----4GlcNAc and GlcNAc beta 1----3GalNAc alpha-O-benzyl (Km values 0.71, 0.83 and 0.53 mM, respectively). Gal beta----3Gal beta 1----4Glc as an acceptor substrate for beta 6-GlcNAc-transferase B does not inhibit the incorporation of GlcNAc in beta 1----6 linkage to the terminal Gal residues of asialo-alpha 1-acid glycoprotein catalyzed by a beta-galactoside beta 1----6-N-acetylglucosaminyltransferase (beta 6-GlcNAc-transferase A) previously described in Novikoff ascites tumor cells [D. H. Van den Eijnden, H. Winterwerp, P. Smeeman & W.E.C.M. Schiphorst (1983) J. Biol. Chem. 258, 3435-3437]. Neither is Triton X-100 at a concentration of 0.8% inhibitory for the activity of beta 6-GlcNAc-transferase A. This activity is absent from hog gastric mucosa microsomes, which has been described to contain high levels of beta 6-GlcNAc-transferase B. [F. Piller, J. P. Cartron, A. Maranduba, A. Veyrières, Y. Leroy & B. Fournet (1984) J. Biol. Chem. 259, 13,385-13,390]. Our results show that Novikoff tumor cells contain two beta-galactoside beta 6-GlcNAc-transferases, which differ in acceptor specificity and tolerance towards Triton X-100. A role for these enzymes in the synthesis of branched polylactosaminoglycans and of O-linked oligosaccharide core structures having blood-group I activity is proposed.
mesh_terms: D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002413:Cations, Divalent / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D005964:Glucosyltransferases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008114:Liver Neoplasms, Experimental / Q000201:enzymology*; D009682:Magnetic Resonance Spectroscopy; D008745:Methylation; D017351:N-Acetylglucosaminyltransferases; D017830:Octoxynol; D011092:Polyethylene Glycols / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013379:Substrate Specificity
chemical_list: D002413:Cations, Divalent; D011092:Polyethylene Glycols; D017830:Octoxynol; D005964:Glucosyltransferases; D017351:N-Acetylglucosaminyltransferases; C053024:beta-1,3-galactosyl-O-glycosyl-glycoprotein beta-1,6-acetylglucosaminyl transferase