Thiosulfate oxidizing enzyme

VIII. OTHER BIOLOGICAL MANGANESE SITES VIII.A. Thiosulfate Oxidizing Enzyme... 

Chan CW, Suzuki I (1994) Thiosulfate oxidation by sulfur-grown Thiobacillus thiooxidans cells, cell-free extracts, and thiosulfate-oxidizing enzyme. Can J Microbiol 40 816-822 Chan L, Pereira MM, Xavier AV, LeGall J (1994) Isolation and characterization of a high molecular weight cytochrome from the sulfate reducing bacterium Desulfovibrio gigas. FEBS Lett 347 295-299... 

Liibben M, Kolmerer B, Saraste M (1992) On archaebacterial terminal oxidase combines core structures of two mitochondrial respiratory complexes. EMBO J 11 805-812 Lundgren DG, Silver M (1980) Ore leaching by bacteria. Annu Rev Microbiol 34 263-283 Lyric RM, Suzuki I (1970a) Enzyme involved in the metabolism of thiosulfate by Thiobacillus thioparus III. Properties of thiosulfate-oxidizing enzyme and proposed pathway of thiosulfate oxidation. Can J Biochem 48 355-363... 

Lyric RM, Suzuki I (1970c) Kinetic studies of sulfite cytochrome c oxidoreductase, thiosulfate-oxidizing enzyme, and adenosine-5 -phosphosulfate reductase from Thiobacillus thioparus. Can J Microbiol 48 594-603... 

Table II summarizes the sources and key properties of isolated HiPIPs, almost all of which have been isolated from photosynthetic organisms, and there has been extensive speculation on their involvement in respiratory electron transport chains (18, 21, 91-93, 95, 96, 102-105). Evidence in support of such a hypothesis has recently emerged from studies of a partially reconstructed reaction center (RC) complex from Rhodoferax fermentans (93, 95). The kinetics of photo-induced electron transfer from HiPIP to the reaction center suggested the formation of a HiPIP-RC complex with a dissociation constant of 2.5 fx,M. In vivo and in vitro studies by Schoepp et al. (94) similarly have demonstrated that the only high-redox-potential electron transfer component in the soluble fraction of Rhodocyclus gelatinosus TG-9 that could serve as the immediate electron transfer donor to the reaction-center-bound C3d ochrome was a HiPIP. In vitro experiments have shown HiPIP to be an electron donor to the Chromatium reaction center (106). Fukumori and Yamanaka (107) also reported that Chromatium vinosum HiPIP is an efficient electron acceptor for a thiosulfate-oxidizing enzyme isolated from that organism.

Suzuki I. 1965b. Incorporation of atmospheric oxygen-18 into thiosulfate by the sulfur-oxidizing enzyme of Thiobacillus thiooxidans. Biochim Biophys Acta 110 97-101. 

For thiosulfate oxidation it is hypothesized that an enzyme system on the cell surface initiates the formation of polythiosulfonic acid and consequently splits the terminal S03" as sulfate. This process may evolve the intermediate of mixed anhydride -S-O-PO4" from phosphorylation (Figure 4). 

Suzuki, I. Incorporation of Atmospheric Oxygen-18 into Thiosulfate by the Sulfur-oxidizing Enzyme of ThiobacUlus thiooxidans. Biochim. Biophys. Acta 110, 97 (1965). 

The thiosulfate reductase/rhodanese/APS reductase system is thus supported by evidence from direct enzyme assay, whole-cell metabolism and energetics, and S-labehng experiments and provides a robust hypothesis to explain thionate oxidation and energy conservation in at least some chemolithotrophs. 

The critical step in the use of multiple sulfur linkages is the availability of HS" from the reduced enzyme system. The HS" could possibly attack the cyclic or the acyclic multiple sulfur linkages through a nucleophilic mechanism. The cleaved sulfide linkages undergo oxidation to sulfite or thiosulfate. This seems a plausible pathway for the oxidation of the sulfur compounds in the present study. 

In Paracoccus vertusus, thiosulfate is oxidized directly to sulfate by the catalysis of an enzyme complex containing several cytochromes c but not cytochrome b (Kelly, 1989). Although sulfite-cytochrome c oxidoreductase occurs in the enzyme complex, the enzyme is thought not to participate in the oxidation of thiosulfate, because the rhodanese activity is not observed with the complex. However, as already indicated, it could be that as the enzyme complex contains a thiosulfatecleaving enzyme strongly bound to both the sulfur-accepting protein and sulfite-cytochrome c oxidoreductase, thiosulfate appears to be oxidized directly to sulfate. 

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