Pathway · 5 proteins
Sugar-phosphate supply
Provide precursors for nucleotides and envelope synthesis.
How it works
- Phosphoglycerate kinase and a type I glyceraldehyde-3-phosphate dehydrogenase act on the triose end of the gluconeogenic route, connecting 3-phosphoglycerate to glyceraldehyde 3-phosphate.
- Transketolase, a second transketolase-domain protein and ribulose-phosphate 3-epimerase rearrange sugar phosphates. This is the non-oxidative chemistry that produces ribose 5-phosphate and erythrose 4-phosphate without an oxidative pentose-phosphate branch.
- Those products feed nucleotide synthesis through PRPP and aromatic amino acids through erythrose 4-phosphate. The annotations describe a reversible rearrangement network, not a single linear stream, and the direction depends on what the cell is making.
Grouped by the atlas’s curated pathway map. The table order is not a proven reaction order.
Its proteins
| Protein | EC | Reaction (UniProt) | Metal or cluster | Amino acids | Certainty |
|---|---|---|---|---|---|
| Glyceraldehyde-3-phosphate dehydrogenase | 1.2.1.12 | D-glyceraldehyde 3-phosphate + phosphate + NAD(+) = (2R)-3-phospho-glyceroyl phosphate + NADH + H(+) | — | 342 | Step named |
| Ferredoxin oxidoreductase alpha subunit | — | — | — | 389 | Step named |
| Phosphoglycerate kinase | 2.7.2.3 | (2R)-3-phosphoglycerate + ATP = (2R)-3-phospho-glyceroyl phosphate + ADP | — | 397 | Step named |
| Ferredoxin oxidoreductase alpha subunit | — | — | — | 404 | Step named |
| Ribulose-phosphate 3-epimerase | 5.1.3.1 | D-ribulose 5-phosphate = D-xylulose 5-phosphate | — | 222 | 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 |
|---|---|---|---|---|---|
| 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 |
Origins
Where would the first sugar phosphates have come from?
The classical prebiotic route to sugars, the formose reaction of formaldehyde, gives a complex mixture with only a small share of ribose.
Starting instead from glycolaldehyde phosphate under strongly alkaline conditions gives a simpler mixture of sugar phosphates, mostly ribose 2,4-diphosphate, and the reaction works well on layered hydroxide minerals.
The better result depends on a starting material that is already phosphorylated, chosen and supplied by the researchers, and on controlled conditions.
It makes related sugars, not this pathway: the cell interconverts specific sugar phosphates through five enzymes acting in a set order.
From the books: Atkins, Gesteland & Cech (eds.), RNA Worlds, p. 35.
The wider question for this part of the cell: origins for building carbon into molecules.
Sources
- Atlas pathway grouping from the VF5 reference-genome system map (Deckert et al. 1998; Braakman & Smith 2014)
Other pathways in this group: Reductive TCA machinery · Pyruvate and acetyl-CoA · Lipid A and outer envelope · Ribose and PRPP supply · Glycolysis / Gluconeogenesis · Amino sugar and nucleotide sugar metabolism · Pentose phosphate pathway · Not yet placed in a pathway