Coenzymes derived from the vitamin folic acid participate in the generation and utilization of single-carbon functional groups-methyl, methylene, and formyl. The vitamin itself was discovered in the 1930s, when it was found that people with a certain type of megaloblastic anemia could be cured by treatment with yeast or liver extracts. The condition is characterized, like all anemias, by reduced levels of erythrocytes. The cells that remain are characteristically large and immature, suggesting a role for the vitamin in cell proliferation and/or maturation. The vitamin is abundant in leafy green vegetables such as spinach, so is named folic acid, from the same root as foliage.

Chemically, folic acid is formed from three distinct moieties: (1) a bicyclic, heterocyclic pteridine ring, 6-methylpterin (see here); (2) p-aminobenzoic acid (PABA), which is itself required for the growth of many bacteria; and (3) glutamic acid. Naturally occurring folates may differ from this compound in the number of glutamate residues per molecule of vitamin, which ranges from three to eight or more. These residues are linked to one another, not by the familiar peptide bond but rather by a modified peptide bond involving the -amino group and the -carboxyl group.

See also: Glutamate as a Precursor of Other Amino Acids, Tetrahydrofolate Coenzymes