One step puts dihydrofolate back to tetrahydrofolate
Route: DHF → THF
When thymidylate synthase makes dTMP, the folate that donated the carbon leaves as dihydrofolate, which has to be reduced back to tetrahydrofolate before it can carry another one-carbon unit. Dihydrofolate reductase uses NADPH to reduce it to tetrahydrofolate, which re-enters the folate cycle. Methotrexate blocks this enzyme in human cells and kills rapidly replicating cells, including tumor cells. Trimethoprim is selective for the microbial enzyme, so it stops bacterial DNA synthesis with little effect on human cells.
Practice this pathway All pathways
| Step | Enzyme | EC | In | Out |
|---|---|---|---|---|
| 1 | Dihydrofolate reductase | 1.5.1.3 | NADPH | NADP⁺ |
Enzyme names and EC numbers are those used on the interactive board. Checked against sources: see the claim table in the repository (tools/pathway_data/checks).