Metabolic pathway
Krebs cycle
Eight reactions in a circle that fully oxidize the two carbons of acetyl-CoA to CO₂. It makes almost no ATP directly: its job is to load electron carriers, three NADH and one FADH₂ per turn, which the respiratory chain will turn into energy.
- In
- Acetyl-CoA + 2 Water + 3 NAD⁺ + FAD + GDP + Inorganic phosphate
- Out
- Coenzyme A + 2 Carbon dioxide + 3 NADH + Proton + FADH₂ + GTP
- Location
- Mitochondrial matrix
Fun facts
- Citrate synthaseThe enzyme changes shape when it binds oxaloacetate: only then does the site where acetyl-CoA fits appear. That way it avoids wasting acetyl-CoA when there is nothing to combine it with.
- α-ketoglutarate dehydrogenaseIt is a close cousin of the pyruvate dehydrogenase complex: the same three-enzyme architecture and the same five coenzymes.
- Succinate dehydrogenaseIt belongs to two pathways at once. Its electrons do not go through NAD⁺: they go straight to ubiquinone, and that is why they yield less ATP.
Reactions
| # | Enzyme | ΔG°′ |
|---|---|---|
| 1 | Citrate synthaseEC 2.3.3.1 · irreversibleAcetyl-CoA + Oxaloacetate + Water → Citrate + Coenzyme A | −32.2kJ/molexergonic |
| 2 | AconitaseEC 4.2.1.3Citrate ⇌ Isocitrate | 13.3kJ/molendergonic |
| 3 | Isocitrate dehydrogenaseEC 1.1.1.42 · irreversibleIsocitrate + NAD⁺ → α-Ketoglutarate + Carbon dioxide + NADH | −8.4kJ/molexergonic |
| 4 | α-ketoglutarate dehydrogenaseEC 1.2.4.2 · irreversibleα-Ketoglutarate + NAD⁺ + Coenzyme A → Succinyl-CoA + Carbon dioxide + NADH | −33.5kJ/molexergonic |
| 5 | Succinyl-CoA synthetaseEC 6.2.1.4Succinyl-CoA + GDP + Inorganic phosphate ⇌ Succinate + Coenzyme A + GTP | −2.9kJ/molexergonic |
| 6 | Succinate dehydrogenaseEC 1.3.5.1Succinate + FAD ⇌ Fumarate + FADH₂ | 0.0kJ/molendergonic |
| 7 | FumaraseEC 4.2.1.2Fumarate + Water ⇌ Malate | −3.8kJ/molexergonic |
| 8 | Malate dehydrogenaseEC 1.1.1.37Malate + NAD⁺ ⇌ Oxaloacetate + NADH + Proton | 29.7kJ/molendergonic |
8 of 8 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. 16