5,10-Methylenetetrahydrofolate

5,10-Methylenetetrahydrofolate (5,10-CH₂-THF) is the substrate used by the enzyme methylenetetrahydrofolate reductase (MTHFR) to generate 5-methyltetrahydrofolate (5-MTHF, or levomefolic acid).

5,10-CH₂-THF can also be used as a coenzyme in the biosynthesis of thymidine. To be specific, it is the C1-donor in the reactions catalyzed by thymidylate synthase and thymidylate synthase (FAD). It also acts as a cofactor in the synthesis of serine from glycine via the enzyme serine hydroxymethyl transferase.