Biosynthesis of bi-, tri-, and tetraantennary oligosaccharides containing alpha-D-galactosyl residues at their nonreducing termini. Branch specificity of the Ehrlich tumor cell alpha(1,3)-galactosyltransferase.

The ability of Ehrlich tumor cell alpha(1,3)-galactosyltransferase to catalyze the incorporation of alpha-D-Gal residues into a specific branch of bi-, tri-, and tetraantennary oligosaccharides has been investigated by acetolysis followed by gel filtration of the fragments on Bio-Gel P-4. Taking advantage of the carbohydrate specificity of the Griffonia simplicifolia I-B4 isolectin, the mono-[14C]alpha-D-Gal derivatives were isolated by affinity chromatography. Analysis of the acetolysis fragments generated by cleavage of the multiantennary substrates indicates that the Ehrlich cell alpha(1,3)-galactosyltransferase acts preferentially on the alpha-D-Man(1,6) arm. This branch is preferred 2.5 times in bi-, 5.6-8.5 times in tri-, and 12.7 times in tetraantennary structures over the alpha-D-Man(1,3) arm. Within the alpha-D-Man(1,6) branch, in turn, there is a 1.3-1.9-fold consistently higher frequency of galactosylation of the beta-D-GlcNAc(1,2) as compared to the beta-D-GlcNAc(1,6) antenna.