Glycosyltransferase involved in biosynthesis of P1, P(k) and the rare NOR antigens of P1PK histo-blood group system (PubMed:10747952, PubMed:10748143, PubMed:22965229, PubMed:26773500, PubMed:29572228, PubMed:33460651). Catalyzes the transfer of galactose from UDP-alpha-D-galactose in an alpha1,4 linkage to lactosylceramide/beta-D-galactosyl-(1->4)-beta-D-glucosyl-(1<->1)- ceramide(d18:1(4E)) to produce globotriaosylceramide/globoside Gb3Cer (d18:1(4E)), also known as P(k) antigen or CD77 (PubMed:10748143, PubMed:10747952, PubMed:26773500, PubMed:29572228, PubMed:22965229). Globoside Gb3Cer/P(k)/CD77 is a root structure in biosynthesis pathway of neutral glycosphingolipids of the globo-series. Broadly expressed in cell membranes of immune cells and other tissues, Gb3Cer/P(k)/CD77 antigen may participate in mechanisms that regulate cell-cell interactions and cell differentiation. In germinal center B cells, Gb3Cer/CD77 interacts with CD19 to drive centroblast-to-centrocyte transition, B cell receptor complex assembly and T follicular helper cell differentiation. In epithelium, Gb3Cer regulates CDH1/E-cadherin- dependent cell-cell adhesion counteracting epithelial-to-mesenchymal transition (By similarity) (PubMed:29572228). Synthesizes P1 glycan epitope (alpha-D-Gal-(1->4)-beta-D-Gal-(1->4)-GlcNAc-R) by transferring a galactose moiety to paragloboside nLc4 or to complex-type N-glycans (PubMed:26773500, PubMed:29572228, PubMed:33460651). Generates the rare NOR1 and NOR2 antigens which carry a Gal(alpha1->4)GalNAc terminal moiety and are both derived from Gb4Cer precursor (PubMed:22965229, PubMed:26773500, PubMed:33460651). Also able to transfer galactose to galactosylceramide/beta-D-Gal-(1<->1')-Cer (PubMed:10748143). {ECO:0000250|UniProtKB:Q67BJ4, ECO:0000269|PubMed:10747952, ECO:0000269|PubMed:10748143, ECO:0000269|PubMed:22965229, ECO:0000269|PubMed:26773500, ECO:0000269|PubMed:29572228, ECO:0000269|PubMed:33460651}. (Microbial infection) P1 and Pk antigens are targeted by Shiga toxins (also called verotoxins), as a way to enter the cell, inhibit protein synthesis and induce apoptosis. . This is the function of ENSG00000128274 (A4GALT, alpha 1,4-galactosyltransferase (P1PK blood group)).