Four steps from glucose 6-phosphate: two NADPH, one CO₂ and a five-carbon sugar phosphate
Route: Glucose 6-phosphate → 6-Phosphoglucono-δ-lactone → 6-Phosphogluconate → Ribulose 5-phosphate → Ribose 5-phosphate
Glucose-6-phosphate dehydrogenase oxidizes the aldehyde carbon of glucose 6-phosphate and makes the first NADPH. The product is a cyclic ester (a lactone), which the lactonase opens with water. 6-Phosphogluconate dehydrogenase then removes the carboxyl carbon as CO₂ and makes the second NADPH, which leaves the five-carbon ribulose 5-phosphate. An isomerase turns this ketose into the aldose ribose 5-phosphate, the sugar in nucleotides. Cells use the NADPH for fatty acid and cholesterol synthesis and to keep glutathione reduced. In the structures shown, the dehydrogenases are human enzymes, while the lactonase and the isomerase come from a bacterium.
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| Step | Enzyme | EC | In | Out |
|---|---|---|---|---|
| 1 | Glucose-6-phosphate dehydrogenase | 1.1.1.49 | NADP⁺ | NADPH |
| 2 | 6-Phosphogluconolactonase | 3.1.1.31 | H₂O | |
| 3 | 6-Phosphogluconate dehydrogenase | 1.1.1.44 | NADP⁺ | NADPH, CO₂ |
| 4 | Ribose-5-phosphate isomerase | 5.3.1.6 |
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).