Fig. 2
From: Folate deficiency as predisposing factor for childhood leukaemia: a review of the literature
Intracellular network of reactions in the metabolism of folates. A variety of related compounds derived from folic acid have specific biochemical functions. Folic acid is first converted into dihydrofolate (DHF) and subsequently into tetrahydrofolate (THF) by the enzyme DHF reductase (DHFR). 5,10-methyleneTHF and 10-formylTHF are responsible for the synthesis of purines; 5,10-methyleneTHF also mediates the conversion of dUMP to dTMP for the synthesis of thymidine, catalysed by the enzyme thymidine synthase (TS). 5-methylTHF is involved for methylation reactions, particularly in the conversion of homocysteine to methionine for the formation of SAM, a major methyl donor for DNA (figure taken from [6])