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.