Metabolic pathway
Urea cycle
Turns surplus ammonia into urea, because free ammonia is toxic. The two nitrogens come from different places: one from ammonia and the other from aspartate. Ornithine goes around and returns to the start; the map draws the cycle stretched out, from ammonia to urea.
- In
- Ammonia + Carbon dioxide + Aspartate + 3 ATP + 2 Water
- Out
- Urea + Fumarate + 2 ADP + AMP + Pyrophosphate + 2 Inorganic phosphate
- Location
- Cytosol
Fun facts
- Carbamoyl phosphate synthetase IIt only works if N-acetylglutamate is present, a molecule made when glutamate is abundant. In other words: the cycle switches on only when there is surplus nitrogen to get rid of.
Reactions
| # | Enzyme | ΔG°′ |
|---|---|---|
| 1 | Carbamoyl phosphate synthetase IEC 6.3.4.16 · irreversibleAmmonia + Carbon dioxide + 2 ATP + Water → Carbamoyl phosphate + 2 ADP + Inorganic phosphate | — |
| 2 | Ornithine transcarbamylaseEC 2.1.3.3 · irreversibleCarbamoyl phosphate + Ornithine → Citrulline + Inorganic phosphate | — |
| 3 | Argininosuccinate synthetaseEC 6.3.4.5 · irreversibleCitrulline + Aspartate + ATP → Argininosuccinate + AMP + Pyrophosphate | — |
| 4 | Argininosuccinate lyaseEC 4.3.2.1 · irreversibleArgininosuccinate → Arginine + Fumarate | — |
| 5 | ArginaseEC 3.5.3.1 · irreversibleArginine + Water → Urea + Ornithine | — |
0 of 5 reactions with a documented ΔG.
Use Shift to select several
The data sheet includes the map. The logo goes at the bottom.
Sources
- Nelson, D. L. & Cox, M. M. (2021). Lehninger. Principios de bioquímica, 8.ª ed., ch. 18