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.
Synonyms: S4I pathway
|Superclasses:||Degradation/Utilization/Assimilation → Inorganic Nutrients Metabolism → Sulfur Compounds Metabolism → Thiosulfate Oxidation|
|Generation of Precursor Metabolites and Energy → Respiration → Aerobic Respiration|
Some taxa known to possess this pathway include : Acidiphilium acidophilum , Acidithiobacillus ferrooxidans , Acidithiobacillus thiooxidans , Advenella mimigardefordensis , Allochromatium vinosum , Pseudaminobacter salicylatoxidans , Thermithiobacillus tepidarius , Thiobacillus aquaesulis , Thiobacillus sp. W5 , Thiobacillus thioparus
Expected Taxonomic Range: Bacteria
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
Several pathways of thiosulfate oxidation are known. The two best understood pathways are the oxidation of thiosulfate directly to sulfate, catalyzed by the Sox enzyme system (see thiosulfate oxidation III (multienzyme complex)), and the oxidation of thiosulfate to tetrathionate (this pathway), which in some organisms may be degraded further to sulfate (see tetrathionate oxidation).
Oxidation to tetrathionate is the most common thiosulfate oxidation pathway. It is found in obligate chemolithotrophs, such as Thermithiobacillus tepidarius, Acidithiobacillus ferrooxidans, and Acidithiobacillus thiooxidans [Eccleston78], in facultative species such as Acidiphilium acidophilum, Thiobacillus aquaesulis, and even in some obligate heterotrophs [Sorokin99].
The enzyme catalyzing this reaction, thiosulfate dehydrogenase, has been partially purified from several organisms, including Acidithiobacillus ferrooxidans [Silver68], Thiobacillus thioparus [Lyric70], and Thermithiobacillus tepidarius [Lu88]. More recently, the enzyme has been completely purified from Thiobacillus sp. W5 [Visser96] and Acidithiobacillus thiooxidans [Nakamura01]. Despite the fact that enzymes from different organisms catalyze the same reaction, only a few structural features are shared by the enzymes that have been characterized.
Certain sulfur-oxidizing organisms can utilize a wide range of polythionates in addition to tetrathionate. For example, Thermithiobacillus tepidarius uses the enzyme trithionate hydrolase to oxidize trithionate to thiosulfate, which is then oxidized to sulfate [Lu88a, Lu88b].
Lu88: Lu, W., Kelly, D.P. (1988). "Cellular location and partial purification of the "thiosulphate-oxidizing enzyme" and "trithionate hydrolyase" from Thiobacillus tepidarius." J. Gen. Microbiol. 134(4): 877-885.
Lu88b: Lu W-P, Kelly DP (1988). "Cellular location and partial purification of the `thiosulphate-oxidizing enzyme' and `trithionate hydrolyase' from Thiobacillus tepidarius." Journal of General Microbiology 134:877-885.
Lyric70: Lyric RM, Suzuki I (1970). "Enzymes involved in the metabolism of thiosulfate by Thiobacillus thioparus. 3. Properties of thiosulfate-oxidizing enzyme and proposed pathway of thiosulfate oxidation." Can J Biochem 48(3);355-63. PMID: 5438323
Nakamura01: Nakamura K, Nakamura M, Yoshikawa H, Amano Y (2001). "Purification and properties of thiosulfate dehydrogenase from Acidithiobacillus thiooxidans JCM7814." Biosci Biotechnol Biochem 65(1);102-8. PMID: 11272812
Sorokin99: Sorokin DY, Teske A, Robertson LA, Kuenen JG (1999). "Anaerobic oxidation of thiosulfate to tetrathionate by obligately heterotrophic bacteria, belonging to the Pseudomonas stutzeri group." FEMS Microbiol Ecol 30(2);113-123. PMID: 10508936
Visser96: Visser JM, de Jong GA, Robertson LA, Kuenen JG (1996). "Purification and characterization of a periplasmic Thiosulfate dehydrogenase from the obligately autotrophic Thiobacillus sp. W5." Arch Microbiol 166(6);372-8. PMID: 9082913
Denkmann12: Denkmann K, Grein F, Zigann R, Siemen A, Bergmann J, van Helmont S, Nicolai A, Pereira IA, Dahl C (2012). "Thiosulfate dehydrogenase: a widespread unusual acidophilic c-type cytochrome." Environ Microbiol 14(10);2673-88. PMID: 22779704
Liu13: Liu YW, Denkmann K, Kosciow K, Dahl C, Kelly DJ (2013). "Tetrathionate stimulated growth of Campylobacter jejuni identifies a new type of bi-functional tetrathionate reductase (TsdA) that is widely distributed in bacteria." Mol Microbiol 88(1);173-88. PMID: 23421726
Meulenberg93: Meulenberg R, Pronk JT, Hazeu W, van Dijken JP, Frank J, Bos P, Kuenen JG (1993). "Purification and partial characterization of thiosulfate dehydrogenase from Thiobacillus acidophilus." Journal of General Microbiology 139:2033-2039.
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