Catalyzes the synthesis of lactosylceramide (LacCer) via the transfer of galactose from UDP-galactose to glucosylceramide (GlcCer) (PubMed:3099851, PubMed:1551920, PubMed:24498430). LacCer is the starting point in the biosynthesis of all gangliosides (membrane-bound glycosphingolipids) which play pivotal roles in the CNS including neuronal maturation and axonal and myelin formation (By similarity). a beta-D-glucosyl-(1<->1')-N-acylsphing-4-enine + UDP-alpha-D-galactose = a beta-D-Gal-(1->4)-beta-D-Glc-(1<->1)-Cer(d18:1(4E)) + H(+) + UDP Inhibited by EDTA. Protein modification; protein glycosylation. Sphingolipid metabolism. Trans cisternae of Golgi stack. High expression in brain and adrenal gland, lower in liver, lung, colon and peripheral white blood cells. Belongs to the glycosyltransferase 7 family. Beta-1,4-galactosyltransferase 6