Three carrier proteins are involved in the transport of Vitamin B12 around the body – Intrinsic Factor (IF), transcobalamin (TC) and haptocorrin (HC).
When transcobalamin and haptocorrin bind Vitamin B12 the resulting complexes are known as holotranscobalamin (HoloTC) and holohaptocorrin (HoloHC).
Only transcobalamin transports Vitamin B12 from its site of absorption in the ileum to tissues and cells. The vitamin is then internalised as the Active-B12 (vitamin B12 bound to transcobalamin) complex via a specific receptor-mediated uptake. This process delivers Vitamin B12 into the cells of the body and provides the vitamin as an essential co-enzyme for vital cellular functions such as DNA synthesis..