Pathway · 2 proteins
Hydrogen oxidation
NiFe hydrogenase subunits provide an electron-donor entry route.
How it works
- A NiFe hydrogenase is encoded with a small subunit, a nickel-dependent large subunit and a b-type cytochrome subunit; the cytochrome subunit connects the active site to the quinone pool.
- Oxidising H2 delivers electrons at low potential, which is what allows the reductive operation of the carbon cycle when the gas is available.
- The module states that the capability is encoded. Hydrogenase expression, nickel insertion and the actual electron flux depend on growth conditions and on the maturation machinery listed in system 16.
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 |
|---|---|---|---|---|---|
| Hydrogenase small subunit | — | — | [4Fe-4S] cluster, [3Fe-4S] cluster | 353 | Step named |
| Hydrogenase large subunit | — | — | Mg(2+), Fe cation, Ni(2+) | 633 | 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 |
|---|---|---|---|---|---|
| Ni/Fe hydrogenase B-type cytochrome subunitHome: Not yet placed in a pathway | — | — | — | 228 | Step named |
Origins
How could hydrogen, the cell's food, have been used before hydrogenase existed?
None of the books searched discusses hydrogenase in an origins context. Metabolism-first proposals assume that hydrogen at vents could reduce carbon dioxide on mineral surfaces.
The hydrogenase of Aquifex holds a nickel-iron centre with carbon monoxide and cyanide attached to the iron. Building that centre takes a separate set of maturation proteins (see the NiFe-hydrogenase maturation pathway), so the enzyme that feeds the cell cannot be made without them.
From the books: Ribas de Pouplana (ed.), The Genetic Code and the Origin of Life, p. 11.
The wider question for this part of the cell: origins for turning hydrogen into usable energy.
Sources
- Atlas pathway grouping from the VF5 reference-genome system map (Deckert et al. 1998; Braakman & Smith 2014)
Other pathways in this group: Quinone-linked electron transfer · ATP synthesis · Oxygen reduction · Oxidative phosphorylation · Not yet placed in a pathway