Methionine synthase connects folate metabolism with vitamin B12 function and helps maintain tissue tetrahydrofolate availability.
Normal metabolic link
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S-adenosyl methionine forms homocysteine when acting as a methyl donor.
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Methionine synthase, a vitamin B12-dependent enzyme, catalyzes remethylation of homocysteine using methyltetrahydrofolate.
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Reduction of methylenetetrahydrofolate to methyltetrahydrofolate is irreversible. Methyltetrahydrofolate is the major source of tetrahydrofolate for tissues, making methionine synthase vital.
Functional folate deficiency
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Vitamin B12 deficiency impairs methionine synthase, causing accumulation of methyltetrahydrofolate that cannot be used.
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This folate trap produces functional folate deficiency secondary to vitamin B12 deficiency.