fig3

Figure 3. Folate-mediated one-carbon metabolism. There are two interrelated cycles in folate metabolism that compete for folate cofactors, namely DNA biosynthesis (represented by blue) and methylation (represented by green). In addition, the trans-sulfuration pathway (depicted in pink) breaks down homocysteine. 5,10-methenylTHF: 5,10-methenyltetrahydrofolate; 5,10-methyleneTHF: 5,10-methylenetetrahydrofolate; 5-methylTHF: 5-methyltetrahydrofolate; 10-formylTHF: 10-formyltetrahydrofolate; AHCY: S-adenosylhomocysteine hydrolase; B₂: riboflavin; B₆: vitamin B₆ (pyridoxine); B₁₂: vitamin B₁₂; BHMT: betaine-homocysteine methyltransferase; CBS: cystathionine β-synthase; CTH: cystathionase, DHF: dihydrofolate; DHFR: dihydrofolate reductase; MAT: methionine adenosyltransferase; MTHFD1: methylenetetrahydrofolate dehydrogenase 1/methenyltetrahydrofolate cyclohydrolase/formyltetrahydrofolate synthetase; MTHFR: methylenetetrahydrofolate reductase; MTR: methionine synthase; R: methyl acceptors, such as DNA or histones; SAH: S-adenosylhomocysteine; SAM: S-adenosylmethionine; SHMT1: serine hydroxymethyltransferase 1; THF: tetrahydrofolate; TYMS: thymidylate synthetase.