Catalyzes the transfer of N-acetylglucosamine (GlcNAc) to core 2 branched O-glycans (PubMed:10430883). Necessary for the synthesis of type III mucin which is specifically produced in the stomach, duodenum, and pancreatic duct (PubMed:10430883). May protect against inflammation-associated gastric adenocarcinomas (By similarity). Protein modification; protein glycosylation. Detected in stomach and pancreas. The conserved DXD motif is involved in enzyme activity. Belongs to the glycosyltransferase 32 family. Alpha-1,4-N-acetylglucosaminyltransferase