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Tetrahydrofolates and their derivatives are a group of B
vitamins collectively known as folates. Folates are essential
cofactors in one-carbon metabolism of almost all living
organisms. Folic acid is the synthetic form of this vitamin
found in supplements and fortified foods. The coenzyme forms
found in nature differ from the synthetic folic acid in the
oxidation state of the pteridine ring where the ring is reduced
to its active form 5,6,7,8-tetrahydrofolate (THF).
Tetrahydrofolates carry one-carbon units at various oxidation
states from the most oxidized formyl group (CHO) to the most
reduced methyl group (CH3). These one-carbon groups
are attached to THF at position N5 of the pteridine ring or N10
of p-aminobenzoate moiety, or as a bridge between the two (Fig
1). In vivo folate cofactors are polyglutamylated and the number
of glutamate residue varies depending on the source of the
vitamin. Polyglutamylation helps in retention of folates within
the cell and is the form preferred by the folate-dependent
enzymes. |
| R1 |
R2 |
Folate |
| CHO |
H |
5-formyl-THF |
| H |
CHO |
10-formyl-THF |
| CH3 |
H |
5-methyl-THF |
| -CH2- |
|
5,10-methylene-THF |
| =CH- |
|
5,10-methenyl-THF |
|