Vitamin B9: Folic Acid

Abstract

Vitamin B9 in food sources may be distributed in different redox states (oxidized, dihydro, tetrahydro in the bicyclic pterin ring system), contain different numbers of oligoglutamate residues, and contain one-carbon units bridging N5 and N10 of the vitamer forms. All these forms are in the folic acid family (folium for Latin for leafy plants – a good source of the vitamin). In the H4-folate oxidation state N5 and N10 are basic and serve as formaldehyde sponge, carrying the one-carbon unit in latent unreactive form. That one-carbon unit is the source of the C5–CH3 group in the deoxythymidylate building block for DNA. Redox interconversion involving NAD+ (B3) or FAD (B2) of the tethered formaldehyde gives either N5–CH3 or N10–CHO folate units that are utilized in methionine or in purine biosynthesis, respectively. Folate deficiency leads to blockade of DNA synthesis and, inter alia, the symptoms of megaloblastic anemia