This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Degradation/Utilization/Assimilation → Inorganic Nutrients Metabolism → Sulfur Compounds Metabolism → Thiosulfate Oxidation|
|Generation of Precursor Metabolites and Energy → Respiration → Aerobic Respiration|
Like fermentation, respiration is a process by which electrons are passed from an electron donor to a terminal electron acceptor. However, in respiration the electrons do not pass directly from the donor to the acceptor. Instead, they pass a number of membrane-bound electron carriers that function as a transport chain, passing the electrons from one to another in steps that follow the electrochemical gradients between the electron donor and the acceptor.
Each oxidized member of the electron transfer chain (which can be a flavoprotein, an electron-transfer quinone, a cytochrome, or other type of electron carrier) can be reduced by the reduced form of the preceding member, and the electrons flow through the chain all the way to the terminal acceptor, which could be oxygen in the case of aerobic respiration, or another type of molecule in anaerobic respiration.
Known terminal acceptors include organic compounds (fumarate, dimethyl sulfoxide, or trimethylamine N-oxide), or inorganic compounds (nitrate, nitrite, nitrous oxide, chlorate, perchlorate, oxidized manganese ions, ferric iron, gold, selenate, arsenate, sulfate and elemental sulfur).
During the process of electron transfer, a proton gradient is formed across the membrane due to three potential processes:
1. The use of some of the energy associated with the electron transfer for active pumping of protons out of the cell.
2. Exporting protons out of the cell during electron-to-hydrogen transfers.
3. Scalar reactions that consume protons inside the cell, or produce them outside the cell, without actually moving a proton from one compartment to another.
Upon passage of protons back into the cytoplasm, they drive multisubunit ATP synthase enzymes that generate ATP.
About This Pathway
The thermoacidophilic archaeon Acidianus ambivalens produces thiosulfate as one of the products of the initial step of the elemental sulfur oxidation pathway, catalyzed by sulfur oxygenase reductase (see superpathway of sulfur oxidation (Acidianus ambivalens)). Thiosulfate is then oxidized by the membrane-bound cytoplasmically oriented thiosulfate:quinone oxidoreductase (TQO) with quinone as electron acceptor, producing tetrathionate. The conversion of thiosulfate to tetrathionate is not limited to Acidianus ambivalens and is typical to acidophilic sulfur-oxidizing archaea, including those that do not possess a TQO enzyme, such as members of the Metallosphaera genus [Liu14]. Thiosulfate is also generated in the bacterium Acidithiobacillus ferrooxidans [Rohwerder03, Brasseur04].
A study of the archaeon Metallosphaera cuprina Ar-4 has shown that the tetrathionate that is formed reacts with a a DsrE3A thiosulfate-carrier protein, forming S-thiosulfonate modifications on two different L-cysteine residues. The thiosulfonates are then transferred to an L-cysteine residue of a TusA sulfur-carrier protein [Liu14]. The exact path of further oxidation is still not known.
Superpathways: superpathway of sulfur oxidation (Acidianus ambivalens)
Brasseur04: Brasseur G, Levican G, Bonnefoy V, Holmes D, Jedlicki E, Lemesle-Meunier D (2004). "Apparent redundancy of electron transfer pathways via bc(1) complexes and terminal oxidases in the extremophilic chemolithoautotrophic Acidithiobacillus ferrooxidans." Biochim Biophys Acta 1656(2-3);114-26. PMID: 15178473
Liu14: Liu LJ, Stockdreher Y, Koch T, Sun ST, Fan Z, Josten M, Sahl HG, Wang Q, Luo YM, Liu SJ, Dahl C, Jiang CY (2014). "Thiosulfate transfer mediated by DsrE/TusA homologs from acidothermophilic sulfur-oxidizing archaeon Metallosphaera cuprina." J Biol Chem 289(39);26949-59. PMID: 25122768
Muller04: Muller FH, Bandeiras TM, Urich T, Teixeira M, Gomes CM, Kletzin A (2004). "Coupling of the pathway of sulphur oxidation to dioxygen reduction: characterization of a novel membrane-bound thiosulphate:quinone oxidoreductase." Mol Microbiol 53(4);1147-60. PMID: 15306018
Rohwerder03: Rohwerder T, Sand W (2003). "The sulfane sulfur of persulfides is the actual substrate of the sulfur-oxidizing enzymes from Acidithiobacillus and Acidiphilium spp." Microbiology 149(Pt 7);1699-710. PMID: 12855721
Dahl13a: Dahl JU, Radon C, Buhning M, Nimtz M, Leichert LI, Denis Y, Jourlin-Castelli C, Iobbi-Nivol C, Mejean V, Leimkuhler S (2013). "The sulfur carrier protein TusA has a pleiotropic role in Escherichia coli that also affects molybdenum cofactor biosynthesis." J Biol Chem 288(8);5426-42. PMID: 23281480
Purschke97: Purschke WG, Schmidt CL, Petersen A, Schafer G (1997). "The terminal quinol oxidase of the hyperthermophilic archaeon Acidianus ambivalens exhibits a novel subunit structure and gene organization." J Bacteriol 179(4);1344-53. PMID: 9023221
Stockdreher14: Stockdreher Y, Sturm M, Josten M, Sahl HG, Dobler N, Zigann R, Dahl C (2014). "New proteins involved in sulfur trafficking in the cytoplasm of Allochromatium vinosum." J Biol Chem 289(18);12390-403. PMID: 24648525
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