Responsible for the synthesis of complex-type N-linked oligosaccharides in many glycoproteins as well as the carbohydrate moieties of glycolipids (PubMed:9405390). Can produce lactose (PubMed:9405390). . This is the function of B4GALT2 (beta-1,4-galactosyltransferase 2, Ensembl gene identifier ENSG00000117411).