Key words Sulfite reductase
Springer Online Journal Archives 1860-2000
Abstract The localization of the dissimilatory sulfite reductase in Desulfovibrio desulfuricans strain Essex 6 was investigated. After treatment of the cells with lysozyme, 90% of the sulfite reductase activity was found in the membrane fraction, compared to 30% after cell rupture with the French press. Sulfite reductase was purified from the membrane (mSiR) and the soluble (sSiR) fraction. On SDS-PAGE, both mSiR and sS iR exhibited three bands at 50, 45 and 11 kDa, respectively. From their UV/VIS properties (distinct absorption maxima at 391, 410, 583, 630 nm, enzymes as isolated) and the characteristic red fluorescence in alkaline solution, mSiR and sSiR were identified as desulfoviridin. Sulfite reductase (HSO3 –→H2S) activity was reconstituted by coupling of mSiR to hydrogenase and cytochrome c 3 from D. desulfuricans. The specific activity of mSiR was 103 nmol H2 min–1 mg–1, and sulfide was the major product (72% of theoretical yield). No coupling was found with sSiR under these conditions. Furthermore, carbon monoxide was used to differentiate between the membrane-bound and the soluble sulfite reductase. In a colorimetric assay, with photochemically reduced methyl viologen as redox mediator, CO stimulated the activity of sSiR significantly. CO had no effect in the case of mSiR. These studies documented th at, as isolated, both forms of sulfite reductase behaved differently in vitro. Clearly, in D. desulfuricans, the six electron conversion HSO3 –→H2S was achieved by a membrane-bound desulfoviridin without the assistance of artificial redox mediators, such as methyl viologen.
Type of Medium: