preferred_name: a 3-O-{beta-D-galactosyl-(1->3)-[N-acetyl-beta-D-glucosaminyl-(1->6)]-N-acetyl-alpha-D-galactosaminyl}-L-threonyl-[protein] + UDP-alpha-D-galactose <=> a 3-O-{beta-D-Gal-(1->4)-beta-D-GlcNAc-(1->6)-[beta-D-Gal-(1->3)]-alpha-D-GalNAc}-L-threonyl-[protein] + UDP + H(+)