Biochemical reactions requiring vitamin B₁₂ as a cofactor

Figure 2. Methionine synthetase (A) transmethylates methyl-tetrahydrofolate (MTHF) and homocysteine to methionine and tetrahydrofolate (THF), important for DNA and myelin synthesis. Methylmalonyl CoA-mutase (B) converts methylmalonyl CoA to succinyl CoA, which enters the Krebs cycle to contribute to lipid and carbohydrate synthesis. Items in red are increased with vitamin B₁₂ deficiency.