Nitrogenase and biological nitrogen fixation.

Biological nitrogen fixation is catalyzed by the nitrogenase enzyme system which consists of two metalloproteins, the iron (Fe-) protein and the molybdenum-iron (MoFe-) protein. Together, these proteins mediate the ATP-dependent reduction of dinitrogen to ammonia. Recent crystallographic analyses of Fe-protein and MoFe-protein have revealed the polypeptide fold and the structure and organization of the unusual metal centers in nitrogenase. These structure provide a molecular framework for addressing the mechanism of the nitrogenase-catalyzed reaction. General features of the nitrogenase system, including conformational coupling of nucleotide hydrolysis, aspects of the cluster structures, and the general spatial organization of redox centers within the protein subunits, are relevant to a wide range of biochemical systems.