Metabolic pathway
Photorespiration
Undoes the mistake RuBisCO makes when it takes oxygen instead of carbon dioxide. It produces nothing useful: it recovers three of every four carbons and loses the other, splitting the work between chloroplast, peroxisome and mitochondrion.
- In
- 2 Ribulose 1,5-bisphosphate + 3 Oxygen + Water + 2 Glutamate + NAD⁺
- Out
- 2 3-Phosphoglycerate + 2 Inorganic phosphate + 2 α-Ketoglutarate + Serine + Ammonia + Carbon dioxide + NADH + Proton
- Location
- Chloroplast stroma
Fun facts
- RuBisCO · oxygenase activityIt is not a flaw evolution failed to fix: when the enzyme appeared there was almost no oxygen in the atmosphere. It was the very success of photosynthesis that created the problem.
- CatalaseIt is one of the fastest enzymes known: each molecule can break down on the order of millions of peroxide molecules per second.
- Glycine cleavage and serine hydroxymethyltransferaseThe ammonia released here is several times more than all the nitrogen the plant fixes anew, so it has to recover every bit of it. A leak at this point would cost it more than the lost carbon.
Reactions
| # | Enzyme | ΔG°′ |
|---|---|---|
| 1×2 | RuBisCO · oxygenase activityEC 4.1.1.39 · irreversibleRibulose 1,5-bisphosphate + Oxygen → 2-Phosphoglycolate + 3-Phosphoglycerate | — |
| 2×2 | Phosphoglycolate phosphataseEC 3.1.3.18 · irreversible2-Phosphoglycolate + Water → Glycolate + Inorganic phosphate | — |
| 3×2 | Glycolate oxidaseEC 1.1.3.15 · irreversibleGlycolate + Oxygen → Glyoxylate + Hydrogen peroxide | — |
| 4 | CatalaseEC 1.11.1.6 · irreversible2 Hydrogen peroxide → 2 Water + Oxygen | — |
| 5×2 | Glutamate-glyoxylate aminotransferaseEC 2.6.1.4Glyoxylate + Glutamate ⇌ Glycine + α-Ketoglutarate | — |
| 6 | Glycine cleavage and serine hydroxymethyltransferaseEC 2.1.2.1 · irreversible2 Glycine + NAD⁺ + Water → Serine + Ammonia + Carbon dioxide + NADH + Proton | — |
0 of 6 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. 20