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

Mo/W formate dehydrogenases catalyze the reversible reduction of CO2 species to formate. It is thought that the substrate is CO2 and not a hydrated species like HCO3−, 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 CO2. A simple, inexpensive and fast method based on protein film electrochemistry is proposed to discriminate whether CO2 or HCO3− is the substrate of any catalyst interacting with an electrode. In this study, CO2 rather than HCO3− is found to be the substrate of both formate dehydrogenase and CO dehydrogenase.