Pathway · 12 proteins
Quinone-linked electron transfer
Membrane redox complexes connect donor and acceptor reactions.
How it works
- NADH-quinone oxidoreductase is annotated as separate subunits (NuoA to NuoN), the dissociated bacterial form of complex I, which takes electrons from NADH and reduces the quinone pool.
- A cytochrome b and a ubiquinol-cytochrome c reductase iron-sulfur subunit carry electrons onward from quinol, and a cytochrome c family member is also listed.
- Quinones are the shared currency between these complexes: several dehydrogenases feed the same pool, so what the pool does next depends on which terminal acceptor is active.
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 |
|---|---|---|---|---|---|
| Rieske-I iron sulfur protein | — | — | [2Fe-2S] cluster | 181 | Step named |
| NADH-quinone oxidoreductase subunit A | 7.1.1.- | a quinone + NADH + 5 H(+)(in) = a quinol + NAD(+) + 4 H(+)(out) | — | 118 | Step named |
| NADH-quinone oxidoreductase subunit B | 7.1.1.- | a quinone + NADH + 5 H(+)(in) = a quinol + NAD(+) + 4 H(+)(out) | [4Fe-4S] cluster | 179 | Step named |
| NADH-quinone oxidoreductase subunit C/D 2 | 7.1.1.- | a quinone + NADH + 5 H(+)(in) = a quinol + NAD(+) + 4 H(+)(out) | — | 586 | Step named |
| NADH-quinone oxidoreductase subunit H | 7.1.1.- | a quinone + NADH + 5 H(+)(in) = a quinol + NAD(+) + 4 H(+)(out) | — | 336 | Step named |
| NADH-quinone oxidoreductase subunit J | 7.1.1.- | a quinone + NADH + 5 H(+)(in) = a quinol + NAD(+) + 4 H(+)(out) | — | 162 | Step named |
| NADH-quinone oxidoreductase subunit K 1 | 7.1.1.- | a quinone + NADH + 5 H(+)(in) = a quinol + NAD(+) + 4 H(+)(out) | — | 100 | Step named |
| NADH dehydrogenase I chain L | — | — | — | 622 | Step named |
| NADH-quinone oxidoreductase subunit N 1 | 7.1.1.- | a quinone + NADH + 5 H(+)(in) = a quinol + NAD(+) + 4 H(+)(out) | — | 464 | Step named |
| NADH dehydrogenase I chain G | — | — | [2Fe-2S] cluster, [4Fe-4S] cluster | 632 | Step named |
| NADH-quinone oxidoreductase subunit F | 7.1.1.- | a quinone + NADH + 5 H(+)(in) = a quinol + NAD(+) + 4 H(+)(out) | FMN, [4Fe-4S] cluster | 426 | Step named |
| NADH-quinone oxidoreductase subunit E | 7.1.1.- | a quinone + NADH + 5 H(+)(in) = a quinol + NAD(+) + 4 H(+)(out) | [2Fe-2S] cluster | 160 | 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 |
|---|---|---|---|---|---|
| Cytochrome bHome: Oxidative phosphorylation | — | — | heme b | 409 | Step named |
Origins
Could electrons have been carried across a membrane before the quinone-using complexes existed?
Quinones such as anthracenedione occur in carbonaceous meteorites. Deamer therefore assumes the prebiotic mixture held quinone-like compounds that could shuttle electrons across membranes and build a proton gradient, and his laboratory is testing this with compounds extracted from the Murchison meteorite.
Deamer himself concludes that we know very little about even the simplest energy reactions available to the first life, and that the question is virtually unexplored by experiment.
In the cell, quinones carry electrons between large membrane complexes built to receive and pass them on. Twelve proteins of the minimal set serve this chain.
From the books: Deamer, Assembling Life, p. 100.
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: ATP synthesis · Oxygen reduction · Hydrogen oxidation · Oxidative phosphorylation · Not yet placed in a pathway