Vitamin B12 transporter protein

The **Vitamin B12 transporter protein** is a general term encompassing several proteins responsible for the binding, transport, and cellular uptake of vitamin B12 (cobalamin) in both mammals and prokaryotes. In mammals, three main transporters are involved: **Intrinsic Factor** (IF) mediates intestinal absorption, **Transcobalamin** (TC, also called Transcobalamin II) is responsible for the transport of B12 in plasma, and **Haptocorrin** (also called Transcobalamin I or R-binder) binds B12 in saliva and protects it in the stomach. Cellular uptake of vitamin B12 in mammals involves specific cell surface receptors for these proteins[1]. In bacteria, several distinct ATP-dependent or facilitated transporters exist, primarily **BtuCDF** (an ABC transporter), **ECF-CbrT** (an ECF-type ABC transporter), and **BtuM** (an S-component with a proposed unique mechanism)[2][3]. Each protein works in concert to allow dietary vitamin B12 to be efficiently absorbed from the intestine, transported in the circulation, and delivered to cells, where B12 acts as a cofactor for essential metabolic enzymes. Disruption of any of these transport steps leads to vitamin B12 deficiency, manifesting as megaloblastic anemia and neurological dysfunction[1]. Mutations in the genes encoding these transporters, or autoimmune targeting (as in pernicious anemia), represent clinically important disease mechanisms. **Note regarding accuracy:** The term "Vitamin B12 transporter protein" is *not* a single canonical protein but rather refers to several related but distinct proteins in different organisms (e.g., Intrinsic Factor, Transcobalamin, Haptocorrin in mammals; BtuCDF, ECF-CbrT, BtuM in bacteria). For precise scientific or therapeutic work, the exact name (e.g., "Transcobalamin") should be specified. Therefore, **is_incorrect** is set to true for the query as stated, due to lack of specificity and potential for ambiguity[1][2].

Other names

TranscobalaminHaptocorrinIntrinsic factorBtuCDF (prokaryotic ABC transporter)ECF-CbrT (prokaryotic ECF-type ABC transporter)BtuM (prokaryotic S-component transporter)Cobalamin transporter

Binding and internalization of vitamin B12 for delivery to cells. Receptor-mediated endocytosis (for transcobalamin and intrinsic factor receptors). ATP-dependent active transport (for BtuCDF and ECF-CbrT in prokaryotes). Facilitated diffusion (for some prokaryotic transporters like BtuM).