In vitro requirements for formate dehydrogenase activity from Desulfovibrio

In Desulfovibrio the protein(s) involved in formate dehydrogenase activity have not been identified or characterized. In situ assays in polyacrylamide gels demonstrated that formate dehydrogenase from either D. gigas or D. vulgaris catalyzed the direct reduction of either methylene blue or benzyl viologen in the presence of formate. Thus, the same protein was active with either electron acceptor. Although the enzyme could be stored in air without irreversible inactivation by O2, activity with either dye was stimulated by the addition of thiols to the assay mixture. In the absence of formate the thiols served as a substrate for the in situ reduction of methylene blue or benzyl viologen by the enzyme. Ammonium sulfate fractionation revealed the presence of a fraction which selectively stimulated activity with either benzyl viologen or cytochrome c3 as the electron acceptor. The stimulating fraction was nondialyzable, heat labile, and unstable upon storage. The fraction from either species could stimulate the formate dehydrogenase activity of the other species. The protein may be of physiological signficance as it increased when the cells were grown on formate, and it stimulated the formate hydrogenlyase system with cytochrome c3 as the electron carrier.