Transcobalamin 1 (TCN1 aka haptocorrin, HC, TCII) is a glycoprotein produced by salivary glands in response to food ingestion (Johnston et al. 1989). TCN1 binds strongly to cobalamin (Cbl aka vitamin B12) and its essential function is protection of the acid-sensitive Cbl while it moves through the stomach. Once food is in the stomach, pepsin and the acidic pH degrade food proteins. Cbl is in its +3 oxidation state in dietary sources.