Biological nitrogen fixation in theory, practice, and reality: a perspective on the molybdenum nitrogenase system

Abstract

Nitrogenase is the sole enzyme responsible for the ATP-dependent conversion of atmospheric dinitrogen into the bioavailable form of ammonia (NH3), making this protein essential for the maintenance of the nitrogen cycle and thus life itself. Despite the widespread use of the Haber–Bosch process to industrially produce NH3, biological nitrogen fixation still accounts for half of the bioavailable nitrogen on Earth. An important feature of nitrogenase is that it operates under physiological conditions, where the equilibrium strongly favours ammonia production. This biological, multielectron reduction is a complex catalytic reaction that has perplexed scientists for decades. In this review, we explore the current understanding of the molybdenum nitrogenase system based on experimental and computational research, as well as the limitations of the crystallographic, spectroscopic, and computational techniques employed. Finally, essential outstanding questions regarding the nitrogenase system will be highlighted alongside suggestions for future experimental and computational work to elucidate this essential yet elusive process.