Properties of formate dehydrogenase from Desulfovibrio gigas

The formate dehydrogenase from extracts of Desulfovibrio gigas was partially purified to a specific activity of 5600 nmol CO2 ∙ min−1 ∙ mg protein−1. Uniquely for a formate dehydrogenase from anaerobes, the enzyme was stable when stored aerobically. Nevertheless, thiols were required in the assay mixture for enzymatic activity. If the enzyme first catalyzed the transfer of electrons from thiols to benzyl viologen (a diaphorase activity), then formate was oxidized rapidly without a lag period. The enzyme had a molecular weight of approximately 240 000, a pH optimum of 7.5–8.0, and a temperature optimum of 56 °C. Activity with cytochrome c3 (molecular radius (Mr) = 13 000) was about twice that with ferredoxin or flavodoxin as the electron acceptor. These results suggest that the formate dehydrogenase from D. gigas can be activated by transferring electrons from thiols to an electron acceptor and uses cytochrome c3 as the natural electron carrier for the oxidation of formate.