Observations on the Bisulfite Reductase (P582) Isolated from Desulfotomaculum nigrificans

The bisulfite reductase (P582) from Desulfotomaculum nigrificans was purified to homogeneity as judged by polyacrylamide gel electrophoresis. By colorimetric methods of analysis, the products of bisulfite reduction by this enzyme were determined to be trithionate, thiosulfate, and sulfide. Of these, trithionate was consistently found to be the major product, whereas the latter two were formed in lesser quantities. When [(35)S]bisulfite was incorporated as substrate, no labeled sulfide was detected. Furthermore, when trithionate and thiosulfate were isolated from reaction mixtures and chemically degraded, (35)S was found in all three sulfur atoms of trithionate; however, only the inner sulfur atom of thiosulfate was radioactive. From these data we conclude that the bisulfite reductase of D. nigrificans reduces bisulfite to trithionate and that thiosulfate and sulfide are endogenous side products of the reaction.