What is the consequence of the irreversibility of the reaction converting N5,N10-methylenetetrahydrofolate to N5-methyltetrahydrofolate in the context of vitamin B12 deficiency?
Explanation
The 'folate trap' hypothesis explains how a vitamin B12 deficiency leads to a functional folate deficiency. Because the conversion of N5,N10-methylenetetrahydrofolate to N5-methyltetrahydrofolate is irreversible, and the only reaction that can recycle the N5-methyl form is the B12-dependent methionine synthase, a lack of B12 causes all folate to accumulate in the unusable N5-methyl form.
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