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. Author manuscript; available in PMC: 2010 Apr 1.
Published in final edited form as: Birth Defects Res A Clin Mol Teratol. 2009 Apr;85(4):314–321. doi: 10.1002/bdra.20542

Figure 2.

Figure 2

Summary of folate-homocysteine metabolism. The primary outputs of the pathway are to 1. support proliferation and DNA repair by the synthesis of nucleotides thymidine via thymidylate synthase (and purines from 10-Formyl THF); 2. support methylation of DNA, RNA, proteins and lipids through the major methyl donor, S-adenosyl methionine (SAM). In this part of the cycle, Hcy is converted to Met by methionine synthase, gaining a methyl group from methyl-THF. * In some tissues, Hcy can also be converted to Met from betaine through conversion of choline to betaine and transfer of a methyl group catalyzed by betaine-homocysteine methyltransferase. DHF=dihydrofolate, THF=tetrahydrofolate, MTHF=methyltetrahydrofolate, Hcy=homocysteine, Met=methionine, SAH=S-adenosyl homocysteine, dUMP=deoxyuridine monophosphate, dTMP=deoxythymidine monophosphate, MTHFR=methyltetrahydrofolate reductase.