Nitrogenase Catalysis & AssemblyBased in part on the article Nitrogenases & the Iron–Molybdenum Cofactor by Paul W. Ludden which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.

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AbstractNitrogenases are metalloenzymes that catalyze biological N2fixation, in which dinitrogen is reduced to ammonia. The best‐characterized molybdenum nitrogenase is composed of the iron (Fe) protein that contains a [4Fe–4S] cluster and the molybdenum–iron (MoFe) protein that contains an [8Fe–7S] cluster (P cluster) and a [Mo–7Fe–9S–homocitrate] cluster (FeMo cofactor).The catalysis of molybdenum nitrogenase occurs in a series of steps. First, the reduced Fe protein binds 2MgATP, undergoes a conformational change, and forms a complex with the MoFe protein. Then, coupled with the hydrolysis of 2MgATP, one electron is transferred from the Fe protein to the MoFe protein within the complex. This is followed by complex dissociation, which allows the enzyme to start the next cycle of electron transfer. Once a sufficient amount of electrons is accumulated on the MoFe protein, substrate reduction takes place.The assembly of the molybdenum nitrogenase Fe protein involves thenifHand at least thenifS, nifU, andnifMgene products that are implicated in the [4Fe–4S] cluster assembly, while the assembly of the MoFe protein requires at least 15nifgene products and involves the biosynthesis and insertion of the FeMo cofactor into the MoFe protein.