Electrocatalysis of CO₂ Reduction by Immobilized Formate Dehydrogenase without a Metal Redox Center

Nicotinamide adenine dinucleotide-dependent formate dehydrogenase from Candida boidinii was immobilized in a 1,2-dimyristoyl-sn-glycero-3-phosphocholine/cholesterol floating lipid bilayer on the gold surface as a biocatalyst for electrochemical CO₂ reduction. We report that, in contrast to common belief, the enzyme can catalyze the electrochemical reduction of CO₂ to formate without the cofactor protonated nicotinamide adenine dinucleotide. The electrochemical data indicate that the enzyme-catalyzed reduction of CO₂ is diffusion-controlled and is a reversible reaction. The orientation and conformation of the enzyme were investigated by surface-enhanced infrared reflection absorption spectroscopy. The α-helix of the enzyme adopts an orientation nearly parallel to the surface, bringing its active center close to the gold surface. This orientation allows direct electron transfer between CO₂ and the gold electrode. The results in this paper provide a new method for the development of enzymatic electrocatalysts for CO₂ reduction.