Vitamin B12

The number of people who follow a vegan or vegetarian diet is increasing, which means that vitamin B₁₂ is also becoming a more frequent topic of public discussion. As B₁₂ is found almost exclusively in animal foods such as meat, fish, eggs and milk, a vegan diet can lead to an undersupply. Absorption disorders, which become more frequent with increasing age, can also lead to an undersupply.

Vitamin B₁₂ is a collective term for a structurally related group of vitamers which have a tetracyclic corrin ring around a cobalt central atom and 5,6-dimethylbenzimidazole as the lower ligand. The individual vitamers differ in the structure of their upper ligand: the four main vitamers are adenosylcobalamin, methylcobalamin, hydroxocobalamin and cyanocobalamin.

Adenosylcobalamin and methylcobalamin play a crucial role in human metabolism as cofactors for two enzymes involved in DNA synthesis and repair, as well as the metabolism of odd-numbered fatty acids and branched-chain amino acids. Hydroxocobalamin and cyanocobalamin are not effective as cofactors themselves, but can be converted into the bioactive forms. Cyanocobalamin is the most stable vitamin and is often added to vegan meat or milk substitute products. Due to the central role that vitamin B₁₂ plays in metabolism, a deficiency leads to various symptoms, such as megaloblastic anemia or damage to the central nervous system, which can lead to neuropathic symptoms, such as impaired coordination of movement, but also to psychiatric disorders such as memory disorders or psychoses. 

The majority of analytical methods known in the literature convert all B₁₂ vitamers into the more stable cyanocobalamin by means of cyanidation and thus determine the total vitamin B₁₂ content. The natural distribution of the individual vitamers in foods is therefore largely unknown. At the Chair of Analytical Food Chemistry, the contents of the four main vitamers are determined individually using stable isotope dilution analysis and 15N-labeled internal standards, which provides a more precise view of the vitamin distribution. 

Our previous projects included the biosynthesis of 15N-lebeled standard for the four main B₁₂-vitamers, as well as the determination of vitamin distribution in liver and meat.