Intrinsic factor (IF), also known as gastric intrinsic factor (GIF), is a glycoprotein produced by the parietal cells of the stomach.It is necessary for the absorption of vitamin B12 (cobalamin) later on in the small intestine. In humans, the gastric intrinsic factor protein is encoded by the GIF gene.Haptocorrin (also known as HC, R protein, and transcobalamin I, TCN1), is a glycoprotein secreted by the salivary glands which binds to vitamin B 12.Vitamin B 12 is acid sensitive and in binding to transcobalamin I it can safely pass through the acidic stomach to the duodenum.ere in the less acidic environment of the small intestine, pancreatic enzymes digest the glycoprotein carrier and vitaminB 12 can then bind to intrinsic factor. This new complex is then absorbed by the epithelial cells (enterocytes) of the ileum.