Human Transcobalamin II Antibody

TCN2 (Transcobalamin II; also TC-2 or TC) is a 42-44 kDa, monomeric, secreted member of the eukaryotic cobalamin transport family of molecules. It is a key player in the transport and absorption of VitB12. TCN1 is a salivary gland protein that binds oral/dietary B12. Once in the stomach, B12 is transferred to IF/Intrinsic Factor, and this complex remains intact during passage through the small intestine. In the distal ileum, the IF:VitB12 complex is internalized following binding to cubam on enterocyte membranes. Once internalized, VitB12 is processed and re-expressed on MRP1 on the enterocyte's basal surface. Here it is transferred to TCN-2, a binding protein secreted by endothelial cells that accounts for the transport of anywhere from 10-30% of circulating VitB12/cobalamin. The TCN2:VitB12 complex is ultimately internalized by cells expressing a membrane-bound, 58 kDa TCN2 receptor termed TCblR. Once internalized, VitB12 is released and converted into cofactors that are involved in methionine biosynthesis. Human TCN2 is synthesized as a 427 amino acid (aa) precursor that contains an 18 aa signal sequence, plus a 409 aa mature region that binds one VitB12 molecule. There are three potential splice variants of TCN2. One contains a Trp substitution for aa 116-143, a second possesses an Ile substitution for aa 336-427, and a third shows a deletion of aa 143-193. There is one Arg-to-Pro transition at position 259 that is correlated with statistically elevated circulating levels of TCN2. Over aa 19-427, human TCN2 shares 72% aa sequence identity with mouse TCN2.