Three steps: the same enzymes as for uracil act on the methylated ring
Route: Thymine → (R)-5,6-Dihydrothymine → (R)-N-Carbamoyl-beta-aminoisobutyrate → (R)-3-Aminoisobutyrate
Dihydropyrimidine dehydrogenase uses NADPH to reduce thymine to 5,6-dihydrothymine. Dihydropyrimidinase opens the ring by adding water, which gives N-carbamoyl-beta-aminoisobutyrate. Beta-ureidopropionase adds a second water and releases the carbamoyl group as carbon dioxide and ammonium, which leaves 3-aminoisobutyrate. The methyl group on carbon 5 makes the intermediates chiral, and the (R) forms are drawn. These are the same three enzymes that break down uracil.
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).