Pyruvate Formate‐Lyase Reaction in Escherichia coli

Fractionation of the cell extract led to partial isolation of four protein fractions that are involved in the dissimilation of pyruvate into acetyl‐CoA and formate: Enzyme I, molecular weight about 140000; enzyme II, molecular weight about 30000, which requires an activation by ferrous ion and dithiols; enzyme III, molecular weight 25000, which is a flavorprotein with flavin‐monoucleotide as coenzyme; and a hitherto less characterized fraction IV. The system in addition comprises the cofactors S ‐adenosylmethionine and thiamine diphosphate. Enzyme III, fraction IV, and thiamine diphosphate could be replaced by the reagents cobaltous ion and thiols which form complexes of high reducing power. This part of the enzyme system obviously plays an auxiliary role, most likely by providing an appropriate redox potential via pyruvate as electron donor. The ability to dissimilate pyruvate was found to arise only and specifically from an interaction between enzyme I, ferrous ion‐activated enzyme II and adenosylmethionine, in presence of either of the above auxiliary systems. Enzyme I is thereby converted into an active form, possibly by reduction, which alone is responsible for the catalysis of the pyruvate dissimilation reaction. The identification of this pyruvate formate‐lyase was accomplished by sedimentation experiments in anaerobic sucrose gradients.