Pathway · 4 proteins
Pyruvate and acetyl-CoA
Connect carbon fixation to central precursor pools.
How it works
- 2-oxoacid:ferredoxin oxidoreductase subunits are annotated here, the enzyme family that interconverts acetyl-CoA and pyruvate with ferredoxin as the electron carrier.
- A pyruvate/oxaloacetate carboxyltransferase and a pyruvate, water dikinase connect pyruvate to oxaloacetate and to phosphoenolpyruvate, the two branches that feed the sugar-phosphate pool and the cycle.
- Both directions matter: the same reactions fix carbon in the reductive direction and release it when the cell oxidises organic substrate. Which direction runs depends on the electron-donor supply, not on the annotation.
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 |
|---|---|---|---|---|---|
| Ferredoxin oxidoreductase gamma subunit | — | — | — | 230 | Step named |
| Ferredoxin oxidoreductase gamma subunit | — | — | — | 241 | Step named |
| Pyruvate carboxylase c-terminal domain | — | — | — | 655 | System only |
| Phosphoenolpyruvate synthase | 2.7.9.2 | pyruvate + ATP + H2O = phosphoenolpyruvate + AMP + phosphate + 2 H(+) | Mg(2+) | 856 | Step named |
Origins
Could pyruvate and acetyl groups have formed from carbon monoxide and carbon dioxide without enzymes?
Metabolism-first proposals hold that carbon monoxide and carbon dioxide were turned into compounds such as pyruvate on mineral surfaces at high temperature and pressure, as at hydrothermal vents. Jack Corliss and John Baross first suggested that life began at such vents after the vents were discovered.
Nick Lane has proposed that simpler molecules, acetyl phosphate in place of ATP and methyl acetate in place of acetyl-CoA, did this work in vent settings.
Tan and Stadler point out that the acetyl-CoA pathway today needs complex enzymes, which differ between methanogens and acetogens, and ATP synthase to turn the proton gradient into ATP. The simpler chemistry Lane proposes has not been demonstrated.
Whether the laboratory conditions used for the individual steps are geologically plausible remains to be established.
From the books: Ribas de Pouplana (ed.), The Genetic Code and the Origin of Life, p. 11; Deamer, Assembling Life, p. 93; Tan & Stadler, The Stairway to Life, PDF p. 132.
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 · Sugar-phosphate supply · 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