Pathway · 3 proteins
Pentose phosphate pathway
Proteins of this group that KEGG places on its “Pentose phosphate pathway” map for Aquifex aeolicus.
How it works
This map turns six-carbon sugar phosphates into five-carbon ones and back. It supplies ribose 5-phosphate for nucleotides and reducing power (NADPH) for building molecules. The proteins here include the dehydrogenases that oxidise glucose 6-phosphate and 6-phosphogluconate, and transaldolase, which shuffles three-carbon units between sugars.
Grouped by KEGG pathway map. The explanation above is the atlas’s own; the map itself covers more organisms than Aquifex.
Its proteins
| Protein | EC | Reaction (UniProt) | Metal or cluster | Amino acids | Certainty |
|---|---|---|---|---|---|
| Transaldolase | 2.2.1.2 | D-sedoheptulose 7-phosphate + D-glyceraldehyde 3-phosphate = D-erythrose 4-phosphate + beta-D-fructose 6-phosphate | D-fructose 6-phosphate | 217 | Step named |
| Glucose-6-phosphate 1-dehydrogenase | 1.1.1.49 | D-glucose 6-phosphate + NADP(+) = 6-phospho-D-glucono-1,5-lactone + NADPH + H(+) | — | 431 | Step named |
| 6-phosphogluconate dehydrogenase | — | — | — | 300 | Step named |
Also part of this pathway
These proteins are described under another pathway, but also take part here.
| Protein | EC | Reaction (UniProt) | Metal or cluster | Amino acids | Certainty |
|---|---|---|---|---|---|
| Ribose 5-phosphate isomerase BHome: Ribose and PRPP supply | — | — | D-ribulose 5-phosphate | 154 | Step named |
| Fructose-1,6-bisphosphate aldolase class IIHome: Glycolysis / Gluconeogenesis | — | — | Zn(2+) | 310 | Step named |
| ATP-dependent 6-phosphofructokinaseHome: Glycolysis / Gluconeogenesis | 2.7.1.11 | beta-D-fructose 6-phosphate + ATP = beta-D-fructose 1,6-bisphosphate + ADP + H(+) | Mg(2+) | 321 | Step named |
| Bifunctional phosphoglucose/phosphomannose isomeraseHome: Glycolysis / Gluconeogenesis | 5.3.1.8; 5.3.1.9 | alpha-D-glucose 6-phosphate = beta-D-fructose 6-phosphate | D-fructose 6-phosphate | 320 | Step named |
| Ribulose-phosphate 3-epimeraseHome: Sugar-phosphate supply | 5.1.3.1 | D-ribulose 5-phosphate = D-xylulose 5-phosphate | — | 222 | Step named |
| 2-amino-3,7-dideoxy-D-threo-hept-6-ulosonate synthaseHome: Phenylalanine, tyrosine and tryptophan biosynthesis | 2.2.1.10 | 1-deoxy-D-threo-hexo-2,5-diulose 6-phosphate + L-aspartate 4-semialdehyde = 2,3-dioxopropyl phosphate + 2-amino-2,3,7-trideoxy-D-lyxo-hept-6-ulosonate | 1-deoxy-D-threo-hexo-2,5-diulose 6-phosphate | 264 | Step named |
| Ribose-phosphate pyrophosphokinaseHome: Purine metabolism | 2.7.6.1 | D-ribose 5-phosphate + ATP = 5-phospho-alpha-D-ribose 1-diphosphate + AMP + H(+) | Mg(2+), D-ribose 5-phosphate | 311 | Step named |
| TransketolaseHome: Not yet placed in a pathway | 2.2.1.1 | D-sedoheptulose 7-phosphate + D-glyceraldehyde 3-phosphate = aldehydo-D-ribose 5-phosphate + D-xylulose 5-phosphate | D-xylulose 5-phosphate, Mg(2+), Ca(2+) | 689 | Step named |
| Deoxyribose-phosphate aldolaseHome: Not yet placed in a pathway | 4.1.2.4 | 2-deoxy-D-ribose 5-phosphate = D-glyceraldehyde 3-phosphate + acetaldehyde | — | 219 | Step named |
| Fructose-1,6-bisphosphate aldolase/phosphataseHome: Fructose and mannose metabolism | 3.1.3.11; 4.1.2.13 | beta-D-fructose 1,6-bisphosphate + H2O = beta-D-fructose 6-phosphate + phosphate | Mg(2+), beta-D-fructose 1,6-bisphosphate | 381 | Unspecified |
Origins
Could the five-carbon sugars this pathway supplies, ribose above all, have formed without it?
Prebiotic sugar chemistry is usually traced to formaldehyde, with the focus on ribose because it is the sugar of RNA. The formose reaction does give ribose, but only as a small share of a complex mixture.
The cell's enzymes move two- and three-carbon units between specific sugar phosphates, making ribose 5-phosphate and reducing power on demand. The uncontrolled chemistry instead gives a broad mixture in which ribose is a minor product.
From the books: Zubay, Origins of Life on Earth and in the Cosmos, PDF p. 185; Atkins, Gesteland & Cech (eds.), RNA Worlds, p. 35.
The wider question for this part of the cell: origins for building carbon into molecules.
Sources
- KEGG map aae00030 (enzymes of this organism highlighted)
Other pathways in this group: Reductive TCA machinery · Sugar-phosphate supply · Pyruvate and acetyl-CoA · Lipid A and outer envelope · Ribose and PRPP supply · Glycolysis / Gluconeogenesis · Amino sugar and nucleotide sugar metabolism · Not yet placed in a pathway