Two steps from IMP: aspartate supplies the amino group, GTP supplies the energy
Route: Inosine monophosphate + Aspartate → Adenylosuccinate → AMP
Adenylosuccinate synthetase replaces the carbonyl oxygen of IMP with the amino group of aspartate. GTP is the phosphoryl donor for this step, so GTP rather than ATP pays for adenine synthesis. Adenylosuccinate lyase then removes fumarate and leaves the amino group on the ring. This is the same lyase that acts on SAICAR in the ring synthesis. The aspartate nitrogen ends up in AMP and the carbon skeleton leaves as fumarate, which enters the Krebs cycle.
Practice this pathway All pathways
| Step | Enzyme | EC | In | Out |
|---|---|---|---|---|
| 1 | Adenylosuccinate synthetase | 6.3.4.4 | GTP | GDP, Pᵢ |
| 2 | Adenylosuccinate lyase | 4.3.2.2 | Fumarate |
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).