FIGURE 2.
A simplified view of cytoplasmic 1C folate metabolism. Not all enzymes are shown. The reactions in blue supply the 1Cs required for DNA synthesis. The reactions in red form part of the folate pathway that produces the methyl donor SAM. A range of methyltransferase enzymes catalyze the transfer of the methyl group (CH3) from SAM to a number of substrates including DNA, i.e., methylation reactions. SAH is an inhibitor of methyltransferase enzymes. MTHFR, methyltetrahydrofolate reductase enzyme; SAH, S-adenosylhomocysteine; SAM, S-adenosylmethionine THF, tetrahydrofolate.