Three steps: reduce the ring, open the ring, then split off the carbamoyl group
Route: Uracil → 5,6-Dihydrouracil → N-Carbamoyl-beta-alanine → Beta-alanine
Dihydropyrimidine dehydrogenase uses NADPH to reduce the double bond between carbons 5 and 6 of uracil, which gives 5,6-dihydrouracil. Dihydropyrimidinase opens the ring by adding water, which gives N-carbamoyl-beta-alanine. Beta-ureidopropionase adds a second water and releases the carbamoyl group as carbon dioxide and ammonium, which leaves beta-alanine. The same three enzymes break down thymine in the next pathway. Patients with a deficiency of dihydropyrimidine dehydrogenase show a severe reaction to the anticancer drug 5-fluorouracil.
Practice this pathway All pathways
| Step | Enzyme | EC | In | Out |
|---|---|---|---|---|
| 1 | Dihydropyrimidine dehydrogenase | 1.3.1.2 | NADPH | NADP⁺ |
| 2 | Dihydropyrimidinase | 3.5.2.2 | H₂O | |
| 3 | Beta-ureidopropionase | 3.5.1.6 | H₂O | CO₂, NH₄⁺ |
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).