The active species of "CO2" utilized in ferredoxin-linked carboxylation reactions

The active species of "CO2", i.e. CO2 or HCO-3(H2CO3) utilized by enzymes catalyzing ferredoxin-linked carboxylation reactions was determined. The enzyme investigated was pyruvate synthase from Clostridium pasteurianum (EC 1.2.7.1; Pyruvate: ferredoxin oxidoreductase). Data were obtained which were compatible with those expected if CO2 is the active species. The dissociation constant (Ks) of the enzyme-CO2 complex was measured. At pH 7.2 Ks for CO2 of pyruvate synthase was found to be approximately 5 mM.