Transfers N-acetylgalactosamine onto globotriaosylceramide (PubMed:10993897). Plays a critical role in preimplantation stage embryonic development (By similarity). globoside Gb3Cer (d18:1(4E)) + UDP-N-acetyl-alpha-D-galactosamine = globoside Gb4Cer (d18:1(4E)) + H(+) + UDP Protein modification; protein glycosylation. Higher expression in heart and brain, and to a lesser extent in lung, placenta, kidney and testis. Lower expression in liver, spleen and stomach. No expression in skeletal muscle. Genetic variation in B3GALNT1 is responsible for the blood group P1PK system [MIM:111400]. Different combinations or absence of the P1PK antigens define 5 different phenotypes: P1, P2, P1(k), P2(k), and P. The P1(k) and P2(k) phenotypes are rare and characterized by lack of the P antigen. B3GALNT1 activity is responsible for the globoside blood group system (GLOB), which is defined by the P antigen [MIM:615021]. Belongs to the glycosyltransferase 31 family. Blood group antigen gene mutation database Beta-1,3-galactosyltransferase 3