Molecular mechanism of pyruvate-ferredoxin oxidoreductases based on data obtained with the Clostridium pasteurianum enzyme

Pyruvate-ferredoxin oxidoreductase oxdises pyruvate in many fermentative microorganisms. The enzyme from Clostridium pasteurianum is an air-sensitive homodiner of 2x120000 daltons, for which pyruvate is the best substrate found among several alpha-ketoacids. Each submit contains eight iron atoms in two [4Fe-4S] clusters. Two distinct EPR signals, possibly associated with two ligand environments, arise from one of these clusters. Binding of pyruvate does not generate a radical. The results reported suggest a scheme for the electron flow in pyruvate ferredoxin oxidoreductases according to which the detailed reaction mechanism depends on the number (even or odd) of [4Fe-4S] clusters present in a given enzyme.