The beta 1,6-GlcNAc transferase activity present in hog gastric mucosal microsomes catalyses site-specific branch formation on a long polylactosamine backbone.

We find that the beta 1,6-GlcNAc transferase activity present in hog gastric mucosal microsomes converts the linear pentasaccharide GlcNAc beta 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4GlcNAc (1) in a site-specific way to the branch-bearing hexasaccharide GlcNAc beta 1-3(GlcNAc beta 1-6)Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4GlcNAc (2). The product is a positional isomer of GlcNAc beta 1-3Gal beta 1-4GlcNAc beta 1-3(GlcNAc beta 1-6)Gal beta 1-4GlcNAc (3), reportedly formed from 1 by another polylactosamine beta 1,6-GlcNAc transferase activity present in human serum (Leppänen et al., Biochemistry, 30 (1991) 9287). Combined use of the two kinds of activities gave in the present experiments the heptasaccharide GlcNAc beta 1-3(GlcNAc beta 1-6)Gal beta 1-4GlcNAc beta 1-3(GlcNAc beta 1-6)Gal beta 1-4GlcNAc (4), in which one of the branches occupies the position of the branch in 2 and the other the position of the branch in 3.