BI-ANTENNARY OLIGO-(N-ACETYLLACTOSAMINO) GLYCANS OF I-TYPE ARE GALACTOSYLATED PREFERENTIALLY AT THE GLCNAC-BETA-1-6GAL LINKED ARMS BY ALPHA-1,3-GALACTOSYLTRANSFERASE OF BOVINE THYMUS

alpha 1,3-Galactosylation of radiolabelled bi-antennary accepters Gal beta 1-4GlcNAc beta 1-3(Gal beta 1-4GlcNAc beta 1-6)Gal-R (R = 1-OH, b eta 1-4GlcNAc or beta 1-4Glc) with bovine thymus alpha 1,3-galactosylt ransferase was studied. At all stages of the reactions the three accep ters reacted faster at the 1 -->, 6 linked arm than at the 1 --> 3 lin ked branch. Hence, in addition to the doubly alpha 1,3-galactosylated products, practically pure Gal beta 1-4GlcNAc beta 1-3(Gal alpha 1-3Ga l beta 1-4GlcNAc beta 1-6)Gal-R could be obtained from the three accep ters in reactions that had proceeded to near completion. The isomeric mono-alpha 1,3-galactosylated products were identified by using exogly cosidases to remove the branches unprotected by alpha 1,3-galactoses a nd by subsequently identifying the resulting linear glycans chromatogr aphically.