Pathway · 2 proteins
Oxygen reduction
Terminal oxidases accept electrons; oxygen is reduced to water.
How it works
- Several terminal oxidases are encoded: cytochrome c oxidase subunits I to III, a b(o/a)3-type cytochrome-c oxidase, a cytochrome d ubiquinol oxidase and a cytochrome-c peroxidase.
- Each takes electrons from a different carrier — cytochrome c for the c-type oxidases, quinol for the d oxidase — and reduces oxygen to water, which is how the chain terminates when oxygen is present.
- Having oxidases with different oxygen affinities lets the cell match respiration to oxygen tension. The annotations show the options available, not which one operates at a given moment.
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 |
|---|---|---|---|---|---|
| Cytochrome c oxidase subunit III | — | — | — | 258 | Step named |
| Cytochrome c oxidase subunit 2 | 7.1.1.9 | 4 Fe(II)-[cytochrome c] + O2 + 8 H(+)(in) = 4 Fe(III)-[cytochrome c] + 2 H2O + 4 H(+)(out) | Cu cation | 236 | 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 c oxidase subunit IHome: Oxidative phosphorylation | — | — | — | 485 | Step named |
Origins
How could a cell reduce oxygen safely before cytochrome oxidase existed?
How it was discovered
- 1931Otto Warburg receives the Nobel Prize for discovering the respiratory enzyme, now called cytochrome oxidase.Garrett & Grisham, Biochemistry, p. 631
The books searched describe no prebiotic route to an oxygen-reducing enzyme.
Cytochrome oxidase holds copper and heme iron in exact positions so that four electrons reach one oxygen molecule together; partial reduction would release damaging oxygen radicals. Both metals have to be delivered and inserted by other proteins.
From the books: Garrett & Grisham, Biochemistry, p. 631; Nelson & Cox, Lehninger Principles of Biochemistry, p. 184.
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 · Hydrogen oxidation · Oxidative phosphorylation · Not yet placed in a pathway