Adenosylcobalamin (AdoCbl), also known as coenzyme B₁₂, cobamamide, and dibencozide, is, along with methylcobalamin (MeCbl), one of the biologically active forms of vitamin B₁₂. Adenosylcobalamin participates as a cofactor in radical-mediated 1,2-carbon skeleton rearrangements. These processes require the formation of the deoxyadenosyl radical through homolytic dissociation of the carbon-cobalt bond. This bond is exceptionally weak, with a bond dissociation energy of 31 kcal/mol, which is further lowered in the chemical environment of an enzyme active site. An

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different molecule ...

that uses adenosylcobalamin as a cofactor is methylmalonyl-CoA mutase (MCM). Further experimentation has also determined adenosylcobalamin's role in regulating expression of some bacterial genes. By binding to CarH, AdoCbl can modulate

carotenoid Carotenoids (), also called tetraterpenoids, are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips, cor ...

genes, which confer warm colors onto various plants. Carotenoid transcription is activated by sunlight, due to the response from AdoCbl. There are other photoreceptors across different bacterial communities, aside from CarH, that also have reactive capability when bound to AdoCbl. For instance, AerR is another factor that uses AdoCbl to give off purple pigmentation. Additional examination of adenosylcobalamin-bound enzymes and the development of this cofactor over time may prove to hold regulatory function of DNA and RNA.

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* {{Vitamin B vitamins Cofactors Organocobalt compounds Vitamers Vitamin B12

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