Gastric intrinsic factor, also known as GIF, belongs to the of the cobalamin transport protein family. It is a glycoprotein produced by the parietal cells of the stomach. Gastric intrinsic factor plays a key role in the absorption of vitamin B12 on in the small intestine. Vitamin B12 bounds to haptocorrin after entry into the stomach. The resulting complex enters the duodenum, where pancreatic enzymes digest haptocorrin. In the less acidic environment of the small intestine, B12 can then bind to gastric intrinsic factor. This new complex travels to the ileum, where special epithelial cells endocytose them. Inside the cell, B12 dissociates once again and binds to another protein, transcobalamin II. The new complex can exit the epithelial cells to enter the liver.
