Structures and Functions of the Nitrogenase Proteins

Abstract

The biological conversion of dinitrogen to ammonia is catalyzed by the nitrogenase enzyme system found in nitrogen-fixing bacteria (Burgess, 1984; Orme-Johnson, 1985; Smith and Eady, 1992). The conventional nitrogenase consists of two component proteins, the iron (Fe-) protein and the molybdenum-iron (MoFe-) protein, that together mediate the ATP dependent reduction of substrates such as dinitrogen and H+ to products. Substrate reduction by nitrogenase involves three basic types of reactions: the reduction of Fe-protein by electron carriers such as flavodoxin; the ATP dependent transfer of single electrons from Fe-protein to MoFe-protein, with a minimal stoichiometry of two molecules of MgATP hydrolyzed per electron transferred; and electron and proton transfer to the substrate, which is almost certainly bound to the FeMo-cofactor of MoFe-protein.