Characterization of a trithionate reductase system from Desulfovibrio vulgaris

A trithionate reductase system was isolated and purified from extracts of Desulfovibrio vulgaris. This system reduced trithionate to thiosulfate and consisted of two proteins. One was bisulfite reductase, an enzyme that reduces bisulfite to trithionate, and the second component was designated TR-1. Both enzymes were required to reduce trithionate to thiosulfate. Flavodoxin and cytochrome c3 from D. vulgaris were tested for their ability to function as electron carriers during trithionate reduction. When molecular hydrogen was the source of electrons for the reduction, both flavodoxin and cytochrome c3 were required. In contrast, when the pyruvate phosphoroclastic system was the reductant, flavodoxin alone participated as the electron carrier. The results indicate that flavodoxin, but not cytochrome c3, interacted with the trithionate reductase system. The cytochrome in the hydrogenase-linked assay functioned as an electron carrier between hydrogenase and flavodoxin.