Differential Reduction of CO2 by Molybdenum and Vanadium Nitrogenases

The molybdenum and vanadium nitrogenases are two homologous enzymes with distinct structural and catalytic features. Previously, it was demonstrated that the V nitrogenase was nearly 700 times more active than its Mo counterpart in reducing CO to hydrocarbons. Herein, a similar discrepancy between the two nitrogenases in the reduction of CO₂ is reported, with the V nitrogenase being capable of reducing CO₂ to CO, CD₄, C₂D₄, and C₂D₆, and its Mo counterpart only capable of reducing CO₂ to CO. Furthermore, it is shown that the V nitrogenase may direct the formation of CD₄ in part via CO₂‐derived CO, but that it does not catalyze the formation of C₂D₄ and C₂D₆ along this route. The exciting observation of a V nitrogenase‐catalyzed C? C coupling with CO₂ as the origin of the building blocks adds another interesting reaction to the catalytic repertoire of this unique enzyme system. The differential activities of the V and Mo nitrogenases in CO₂ reduction provide an important framework for systematic investigations of this reaction in the future.