Metabolic pathway
Pentose phosphate pathway
It is not for getting energy, but for two things glycolysis does not give: NADPH, which pays for building fats and for the defence against oxidation, and ribose-5-phosphate, the backbone of every nucleotide. What is left over goes back to glycolysis as fructose-6-phosphate and glyceraldehyde-3-phosphate.
- In
- 3 Glucose 6-phosphate + 6 NADP+ + 3 Water
- Out
- 6 NADPH + 6 Proton + 3 Carbon dioxide + 2 Fructose 6-phosphate + Glyceraldehyde 3-phosphate
- Location
- Cytosol
Fun facts
- Glucose-6-phosphate dehydrogenaseIts deficiency is the most widespread enzyme disorder in the world, with several hundred million people affected. Without enough NADPH, the red blood cell cannot neutralize oxidants and breaks apart.
- TransketolaseIt needs thiamine, vitamin B1. Without it this enzyme is among the first to fail, and nervous tissue, which depends heavily on this pathway, is the first to notice.
Reactions
| # | Enzyme | ΔG°′ |
|---|---|---|
| 1×3 | Glucose-6-phosphate dehydrogenaseEC 1.1.1.49 · irreversibleGlucose 6-phosphate + NADP+ → 6-Phosphoglucono-δ-lactone + NADPH + Proton | −17.6kJ/molexergonic |
| 2×3 | LactonaseEC 3.1.1.31 · irreversible6-Phosphoglucono-δ-lactone + Water → 6-Phosphogluconate + Proton | −21.0kJ/molexergonic |
| 3×3 | 6-phosphogluconate dehydrogenaseEC 1.1.1.44 · irreversible6-Phosphogluconate + NADP+ → Ribulose 5-phosphate + Carbon dioxide + NADPH | — |
| 4 | Ribose-5-phosphate isomeraseEC 5.3.1.6Ribulose 5-phosphate ⇌ Ribose 5-phosphate | — |
| 5×2 | Ribulose-5-phosphate 3-epimeraseEC 5.1.3.1Ribulose 5-phosphate ⇌ Xylulose 5-phosphate | — |
| 6 | TransketolaseEC 2.2.1.1Xylulose 5-phosphate + Ribose 5-phosphate ⇌ Sedoheptulose 7-phosphate + Glyceraldehyde 3-phosphate | — |
| 7 | TransaldolaseEC 2.2.1.2Sedoheptulose 7-phosphate + Glyceraldehyde 3-phosphate ⇌ Erythrose 4-phosphate + Fructose 6-phosphate | — |
| 8 | TransketolaseEC 2.2.1.1Xylulose 5-phosphate + Erythrose 4-phosphate ⇌ Fructose 6-phosphate + Glyceraldehyde 3-phosphate | — |
2 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. 14