Translations:Vitamin B12/64/en

In humans, two major coenzyme B₁₂-dependent enzyme families corresponding to the first two reaction types, are known. These are typified by the following two enzymes:

Simplified schematic diagram of the folate methionine cycle. Methionine synthase transfers the methyl group to the vitamin and then transfers the methyl group to homocysteine, converting that to methionine.