Pyruvate:ferredoxin oxidoreductase (PFO) is an enzyme of the central fermentation pathway of Clostridium acetobutylicum that plays an important role in the redox regulation of the organism. The enzyme purified from Clostridium acetobutylicum strain DSM 1731 contains an Fe-S cluster that mediates electron flow from pyruvate to ferredoxin. The enzyme also contains thiamin diphosphate that is not covalently attached [Meinecke89, Woods93]. The pure enzyme exhibited a specific activity of 25 U/mg of protein, and was sensitive to oxygen. The enzyme showed 12.5% of the activity with 2-oxobutanoate, and no activity with 2-oxoglutarate. Ferredoxin isolated from Clostridium acetobutylicum could be used as physiological electron acceptor [Meinecke89].