Haptocorrin

Haptocorrin also known as transcobalamin-1 (TC-1) or cobalophilin is a protein that in humans is encoded by the TCN1 gene. The essential function of haptocorrin is protection of the acid-sensitive vitamin B₁₂ while it moves through the stomach.

Function

Haptocorrin (HC), also commonly known as the R-protein, or the R-factor, or previously referred to as transcobalamin I, is a unique glycoprotein produced by the salivary glands of the oral cavity, in response to ingestion of food. This protein binds strongly to vitamin B₁₂ in what is perhaps an intricate yet necessary evolutionary mechanism to protect this vitamin from the acidic environment of the stomach. Vitamin B₁₂ is an essential water-soluble vitamin, the deficiency of which creates anemia (macrocytic anemia), decreased bone marrow cell production (anemia, pancytopenia), neurological problems, as well as metabolic issues (methylmalonyl-CoA acidosis).

Vitamin B₁₂ is therefore an important vitamin for the body to absorb. Despite its vital role however, vitamin B₁₂ is structurally very sensitive to the hydrochloric acid found in the stomach secretions, and easily denatures in that environment before it has a chance to be absorbed by the small intestine. Found in fresh animal products (such as liver), vitamin B₁₂ attaches haptocorrin, which has a high affinity for its molecular structure. Coupled together vitamin B₁₂ and haptocorrin create a complex. This Haptocorrin-B₁₂ complex is impervious to the insult of the stomach acid, and passes on via the pylorus to the duodenum. In the duodenum pancreatic proteases (a component of pancreatic juice) cleave haptocorrin, yet again releasing vitamin B₁₂ in its free form.