Two steps from ADP: ribonucleotide reductase removes the 2' hydroxyl, then a kinase adds a phosphate
Route: ADP → Deoxyadenosine diphosphate → Deoxyadenosine triphosphate
Ribonucleotide reductase removes the 2' hydroxyl from the ribose of a nucleoside diphosphate. The same enzyme acts on ADP, GDP, CDP and UDP, which gives the four deoxy diphosphates. Thioredoxin carries electrons from NADPH to the enzyme and ends up oxidized. Which substrate the enzyme takes depends on the nucleoside triphosphate bound at a separate regulatory site: dATP directs it to the pyrimidines CDP and UDP, dTTP directs it to GDP, and dGTP directs it to ADP. This keeps the four DNA building blocks in proportion. High dATP also switches the whole enzyme off, which the structure shown here has bound. Nucleoside diphosphate kinase then adds the third phosphate and gives dATP. The structure is the large subunit of the human enzyme. The small subunit carries the radical that starts the reaction and is not shown.
Practice this pathway All pathways
| Step | Enzyme | EC | In | Out |
|---|---|---|---|---|
| 1 | Ribonucleotide reductase | 1.17.4.1 | Trx-(SH)₂ | Trx-S₂, H₂O |
| 2 | Nucleoside diphosphate kinase | 2.7.4.6 | ATP | ADP |
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).