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. 2024 Jun 14;16(12):1872. doi: 10.3390/nu16121872

Figure 1.

Figure 1

The process of dietary folic acid metabolism. After dietary folic acid is absorbed, it is reduced to DHF by DHFR and regenerated into THF by MTHFR. Meanwhile, the polyglutamylated folates PteGlu3–5 are decomposed into monoglutamate folate PteGlu, and transformed into THF. In the folate cycle, a released 1C unit from serine or glycine is transferred to THF, forming 5,10-MTHF. 5,10-MTHF is reduced to the active 5-MTHF under the action of MTHFR. THF carries 1C units to form 5,10-MTHF and 5-MTHF. 5,10-MTHF converts dUMP to dTMP, which is necessary for DNA synthesis and repair. In the methionine cycle, methionine is catalyzed to form SAM, SAM is demethylated to produce SAH, which is deadenosined to form Hcy. Released CH3 is the main source of methylation of DNA and protein. Methionine can be regenerated from Hcy in the presence of MTR and VitB12.