Role of Thiosulfate in Bisulfite Reduction as Catalyzed byDesulfovibrio vulgaris

Abstract

Studies with ³⁵S-labeled substrates were conducted to investigate the pathway involved in the reduction of sulfite to sulfide by cell-free extracts of the sulfate-reducing organism Desulfovibrio vulgaris. The results showed that accumulation of thiosulfate occurred when crude extracts were incubated under appropriate conditions with sulfite as substrate. With labeled sulfite as substrate, thiosulfate with equal distribution of radioactivity in both sulfur atoms was formed. When the rates of formation of ³⁵S²⁻ from inner- and outer-labeled thiosulfate were compared, the rate of formation from outer-labeled thiosulfate was greater. Time studies with S-³⁵SO₃²⁻ showed an increase of ³⁵S²⁻ with time and an increasing ratio of doubly labeled to inner labeled thiosulfate remaining in the reaction mixture. From these studies it is concluded that thiosulfate is a stable intermediate formed from sulfite during the reduction of sulfate by D. vulgaris. Both sulfur atoms are derived from sulfite; during the utilization of thiosulfate, the outer sulfur is reduced to sulfide and the inner sulfur recycles through a sulfite pool.