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. Author manuscript; available in PMC: 2007 May 14.
Published in final edited form as: Biochemistry. 2006 Apr 18;45(15):4808–4818. doi: 10.1021/bi052294c

Figure 1.

Figure 1

Segments of the pathways of one-carbon metabolism showing the fates of methylenetetrahydrofolate. In the AdoMet cycle on the left, CH2-H4folate is used to form methionine by the dual action of methylenetetrahydrofolate reductase (MTHFR) and methionine synthase (MS); in the thymidylate synthase (TS) cycle on the right, the methylene group is utilized for thymidylate biosynthesis. Dihydrofolate reductase (DHFR) catalyzes the conversion of dihydrofolate (H2folate) to tetrahydrofolate (H4folate), and CH2-H4folate is regenerated by the enzyme serine hydroxymethyl transferase (SHMT). The conversion of homocysteine to methionine catalyzed by betaine-homocysteine methyltransferase is not shown here.