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. sulfite + hydrogen sulfide + a quinone = thiosulfate + a quinol

MNPSQHAEQFQSQLANYVPQFTPEFWPVWLIIAGVLLVGMWLVLGLHALLRARGVKKSAT DHGEKIYLYSKAVRLWHWSNALLFVLLLASGLINHFAMVGATAVKSLVAVHEVCGFLLLA CWLGFVLINAVGDNGHHYRIRRQGWLERAAKQTRFYLFGIMQGEEHPFPATTQSKFNPLQ QVAYVGVMYGLLPLLLLTGLLCLYPQAVGDVFPGVRYWLLQTHFALAFISLFFIFGHLYL CTTGRTPHETFKSMVDGYHRH265

	12427953	Specificity of respiratory pathways involved in the reduction of sulfur compounds by Salmonella enterica.Hinsley AP, Berks BC	The tetrathionate (Ttr) and thiosulfate (Phs) reductases of Salmonella enterica LT2, together with the polysulfide reductase (Psr) of Wolinella succinogenes, are unusual examples of enzymes containing a molybdopterin active-site cofactor since all formally catalyse sulfur-sulfur bond cleavage. This is in contrast to the oxygen or hydrogen transfer reactions exhibited by other molybdopterin enzymes. Here the catalytic specificity of Ttr and Phs has been compared using both physiological and synthetic electron-donor systems. Ttr is shown to catalyse reduction of trithionate but not sulfur or thiosulfate. In contrast, Phs cannot reduce tetrathionate or trithionate but allows whole cells to utilize elemental sulfur as an electron acceptor. Mechanisms are proposed by which the bacterium is able to utilize an insoluble sulfur substrate by means of reactions at the cytoplasmic rather than the outer membrane.	2002
0	7751291	Sequence analysis of the phs operon in Salmonella typhimurium and the contribution of thiosulfate reduction to anaerobic energy metabolism.Heinzinger NK, Fujimoto SY, Clark MA, Moreno MS, Barrett EL	The phs chromosomal locus of Salmonella typhimurium is essential for the dissimilatory anaerobic reduction of thiosulfate to hydrogen sulfide. Sequence analysis of the phs region revealed 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 predicted products of phsA and phsB exhibited significant homology with the catalytic and electron transfer subunits of several other anaerobic molybdoprotein oxidoreductases, including Escherichia coli dimethyl sulfoxide reductase, nitrate reductase, and formate dehydrogenase. Simultaneous comparison of PhsA to seven homologous molybdoproteins revealed numerous similarities among all eight throughout the entire frame, hence, significant amino acid conservation among molybdoprotein oxidoreductases. Comparison of PhsB to six other homologous sequences revealed four highly conserved iron-sulfur clusters. The predicted phsC product was highly hydrophobic and similar in size to the hydrophobic subunits of the molybdoprotein oxidoreductases containing subunits homologous to phsA and phsB. Thus, phsABC appears to encode thiosulfate reductase. Single-copy phs-lac translational fusions required both anaerobiosis and thiosulfate for full expression, whereas multicopy phs-lac translational fusions responded to either thiosulfate or anaerobiosis, suggesting that oxygen and thiosulfate control of phs involves negative regulation. A possible role for thiosulfate reduction in anaerobic respiration was examined. Thiosulfate did not significantly augment the final densities of anaerobic cultures grown on any of the 18 carbon sources tested. on the other hand, washed stationary-phase cells depleted of ATP were shown to synthesize small amounts of ATP on the addition of the formate and thiosulfate, suggesting that the thiosulfate reduction plays a unique role in anaerobic energy conservation by S typhimurium.	1995

Heinzinger N K , Fujimoto S Y , Clark M A , et al. Sequence analysis of the phs operon in Salmonella typhimurium and the contribution of thiosulfate reduction to anaerobic energy metabolism.[J]. Journal of Bacteriology, 1995, 177(10):2813-2820.