Formate Dehydrogenases Reduce CO₂ Rather than HCO₃⁻: An Electrochemical Demonstration

Mo/W formate dehydrogenases catalyze the reversible reduction of CO 2 species to formate. It is thought that the substrate is CO 2 and not a hydrated species like HCO 3 − , but there is still no indisputable evidence for this, in spite of the extreme importance of the nature of the substrate for mechanistic studies. We devised a simple electrochemical method to definitively demonstrate that the substrate of formate dehydrogenases is indeed CO 2 .