Function
Methionine synthase catalyzes the final step in the regeneration of methionine from homocysteine.
Methionine synthase contains the cofactor methylcobalamin (MeB12) and uses the substrates N5-methyl-tetrahydrofolate (N5-mTHF, or levomefolic acid) and homocysteine.
The enzyme works in two steps in a ping-pong reaction. First, methylcobalamin is formed by a methyl group transfer from N5-mTHF with formation of MeB12 and tetrahydrofolate (THF). In the second step, MeB12 transfers this methyl group to homocysteine, regenerating the cofactor cobalamin and releasing the product methionine.
Methionine synthase is the only mammalian enzyme that metabolizes 5-mTHF to regenerate the active cofactor THF. Deficiency in methionine synthase function may be due to genetic mutations, reduced levels of its cobalamin cofactor (vitamin B12), or decreased levels of the enzyme (methionine synthase) reductase (required for the sustained activity of methionine synthase).
Read more about this topic: Methionine Synthase
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