CO2 reduction to formate by NADH catalysed by formate dehydrogenase from Pseudomonas oxalaticus.

The direct reduction of CO2 to formate is catalysed by formate: NAD oxidoreductase in the presence of substrate amounts of NADH. Proof for this reaction is supplied by the detection of a CO2-dependent NADH oxidation, and by the identification of [14c] formate as the product of a NADH-dependent reduction of [14c]carbonate. The enzyme-catalysed CO2 reduction by NADH attains the equilibrium predicted by thermodynamic considerations, a state which is also reached from the formate side. The Michaelis constant for CO2 is about 40 mM indicating the low affinity of the enzyme for this substrate. The corresponding value for formate is 0.1 mM. Under the special conditions employed the enzyme catalyses the formate oxidation about 30 times faster than the CO2 reduction. That CO2 and not HCO3- is the active species in the reduction was shown by comparing the ph dependency of the velocities of the forward and back reactions and by observing the kinetics of CO2 reduction during the simultaneous attainment of the CO2-HCO3- equilibrium.