Vitamin B12 transport proteins and cofactor-dependent enzymes (B12-TCE)

Vitamin B12 (cobalamin) transport proteins and cofactor-dependent enzymes constitute a complex physiological system essential for cellular metabolism, DNA synthesis, and nervous system maintenance. The transport component includes haptocorrin, gastric intrinsic factor, and transcobalamin II, which sequentially bind cobalamin to facilitate its absorption in the ileum and subsequent delivery to peripheral tissues via the CD320 receptor [1][2]. Intracellularly, cobalamin is processed into two active cofactors: methylcobalamin and adenosylcobalamin. Methylcobalamin is required by the enzyme methionine synthase for the remethylation of homocysteine to methionine, a reaction vital for the S-adenosylmethionine (SAM) cycle and nucleotide biosynthesis [3]. Adenosylcobalamin serves as a cofactor for methylmalonyl-CoA mutase, which facilitates the conversion of methylmalonyl-CoA to succinyl-CoA within the mitochondria, supporting the citric acid cycle and fatty acid metabolism [4]. Dysfunctions in these proteins, whether due to nutritional deficiency, autoimmune destruction (pernicious anemia), or genetic mutations, result in clinical manifestations such as megaloblastic anemia and progressive demyelination [5]. Pharmacological management typically involves the administration of cobalamin derivatives to restore enzymatic function, though certain drugs like metformin and proton pump inhibitors can negatively impact the transport system's efficiency [6].

Other names

Cobalamin transport and metabolism systemVitamin B12 metabolic pathwayCbl transport proteinsVitamin B12-dependent enzymesIntrinsic factor-cobalamin complex systemTranscobalamin-mediated B12 uptake

Exogenous supplementation of cobalamin derivatives to serve as essential enzymatic cofactors; pharmacological interference with gastric acid or intestinal transporters reducing B12 bioavailability; chemical inactivation of cofactors by anesthetic gases.