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Abstract

Abstract Nitrogenases are a family of metalloenzymes that catalyse a key step in the global nitrogen cycle: the adenosine triphosphate (ATP)-dependent reduction of dinitrogen (N2) to ammonia (NH3). The molybdenum (Mo)-nitrogenase is the best characterised member of this enzyme family. It is a two-component system comprising an iron (Fe) protein and a molybdenum-iron (MoFe) protein, each containing FeS cluster(s) which are responsible for the electron flow during the process of substrate reduction. This article provides an overview of the current knowledge on the structure, assembly and catalysis of Mo-nitrogenase, as well as a brief discussion of alternative substrates of nitrogenase and other members in this enzyme family. Key Concepts: The nitrogenase complex consists of two Fe protein dimers and one MoFe protein tetramer; each component harbours metallocluster(s) that mediate electron flow to the active centre within the complex. The active centre of Mo-nitrogenase, designated the FeMoco or the M-cluster, is a [MoFe7S9C-homocitrate] cluster. Electrons are transferred from the [Fe4S4] cluster in the Fe protein to the P-cluster and then the M-cluster in the MoFe protein, where substrate reduction occurs. Nitrogenase catalyses the ATP-dependent reduction of dinitrogen (N2) to ammonia (NH3) under ambient temperature and pressure. Nitrogenase has been found to catalyse the reduction of alternative substrates, such as H+, N3 −, CN−, C2H2 and CO.