The enzyme, characterized from the bacterium Salmonella enterica, is similar to EC 1.17.5.3, formate dehydrogenase-N. It contains a molybdopterin-guanine dinucleotide, five [4Fe-4S] clusters and two heme b groups. The reaction occurs in vivo in the direction of thiosulfate disproportionation, which is highly endergonic. It is driven by the proton motive force that occurs across the cytoplasmic membrane.
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SYSTEMATIC NAME
IUBMB Comments
sulfite,hydrogen sulfide:quinone oxidoreductase
The enzyme, characterized from the bacterium Salmonella enterica, is similar to EC 1.17.5.3, formate dehydrogenase-N. It contains a molybdopterin-guanine dinucleotide, five [4Fe-4S] clusters and two heme b groups. The reaction occurs in vivo in the direction of thiosulfate disproportionation, which is highly endergonic. It is driven by the proton motive force that occurs across the cytoplasmic membrane.
gene cluster phsBCDEF is essential for the anaerobic production of hydrogen sulfide from thiosulfate. Five potential translationally coupled open reading frames are present. Their putative protein products constitute a membrane-associated electron transport chain which contains proteins potentially capable of ligating iron-sulfur clusters and heme
mutants defective in phs and chlA also lack a methyl viologen-linked thiosulfate reductase activity present in anaerobically grown wild-type cultures. Temperature-sensitive phs mutants produce H2S and methyl viologen-linked thiosulfate reductase at 30°C but not at 42°C. The reductases in all such mutants grown at 30°C are as thermostable as the wild-type enzyme and do not differ in electrophoretic relative mobility. The phs gene may encode a regulatory protein essential for the reduction of thiosulfate to hydrogen sulfide
the Phs chromosomal locus of Salmonella typhimurium is essential for the dissimilatory anaerobic reduction of thiosulfate to hydrogen sulfide. The Phs region is a functional operon with three open reading frames, designated PhsA, PhsB, and PhsC, which encode peptides of 82.7, 21.3, and 28.5 kDa, respectively. The products of PhsA and PhsB exhibit significant homology with the catalytic and electron transfer subunits of anaerobic molybdoprotein oxidoreductases. The predicted PhsC product is highly hydrophobic and similar in size to the hydrophobic subunits of the molybdoprotein oxidoreductases containing subunits homologous to PhsA and PhsB. PhsABC appears to encode thiosulfate reductase
thiosulfate reductase activity depends on the proton motive force across the cytoplasmic membrane. The proton motive force drives endergonic electron flow within the enzyme by a reverse loop mechanism. Thiosulfate reductase is able to catalyze the combined oxidation of sulfide and sulfite to thiosulfate in a reverse of the physiological reaction. In contrast to the forward reaction, the exergonic thiosulfate-forming reaction is independent of the proton motive force
the Phs chromosomal locus of Salmonella typhimurium is essential for the dissimilatory anaerobic reduction of thiosulfate to hydrogen sulfide. The Phs region is a functional operon with three open reading frames, designated PhsA, PhsB, and PhsC, which encode peptides of 82.7, 21.3, and 28.5 kDa, respectively. The products of PhsA and PhsB exhibit significant homology with the catalytic and electron transfer subunits of anaerobic molybdoprotein oxidoreductases. The predicted PhsC product is highly hydrophobic and similar in size to the hydrophobic subunits of the molybdoprotein oxidoreductases containing subunits homologous to PhsA and PhsB. PhsABC appears to encode thiosulfate reductase
Escherichia coli expressing thiosulfate reductase genes (phsABC) from Salmonella typhimurium is able to remove significant amounts of heavy metals from the medium within 24 h: 99% of zinc up to 500 microM, 99% of lead up to 200 microM, 99% of 100 icroM and 91% of 200 icroM cadmium. In a mixture of 100 microM each of cadmium, lead, and zinc, the strain removes 99% of the total metals from solution within 10 h. Cadmium is removed first, lead second, and zinc last
Escherichia coli strains harboring thiosulfate reductase gene phsABC expression constructs show higher thiosulfate reductase activity and produce significantly more sulfide than the control strains under both aerobic and anaerobic conditions. The most effecitve expression construct produces thiosulfate reductase at the highest level and removes the most cadmium from solution under anaerobic conditions: 98% of all concentrations up to 150 microM and 91% of 200 microM. The metal removed from solution precipitates as a complex of cadmium and sulfur, most likely cadmium sulfide
Escherichia coli strains harboring thiosulfate reductase gene phsABC expression constructs show higher thiosulfate reductase activity and produce significantly more sulfide than the control strains under both aerobic and anaerobic conditions. The most effecitve expression construct produces thiosulfate reductase at the highest level and removes the most cadmium from solution under anaerobic conditions: 98% of all concentrations up to 150 microM and 91% of 200 microM. The metal removed from solution precipitates as a complex of cadmium and sulfur, most likely cadmium sulfide
Engineering hydrogen sulfide production and cadmium removal by expression of the thiosulfate reductase gene (phsABC) from Salmonella enterica serovar typhimurium in Escherichia coli
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Enzyme Nomenclature
1.8.5.5 thiosulfate reductase (quinone)
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