The enzymology of biological nitrogen fixation

摘要

The determination of the X-ray crystal structures of the two proteins which make up nitrogenase, the molybdenum-containing enzyme which catalyses biological nitrogen fixation, is an important advance affecting many aspects of chemical and biochemical research in this area. The Fe protein which acts as an ATP-dependent electron donor to the MoFe protein, has a single 4Fe4S centre bridging the two subunits. The MoFe protein, which contains the active site, has been shown to have redox centres with unique structures which have no counterpart in enzymes other than nitrogenase. Although all nitrogen fixing organisms have a Mo-nitrogenase, it is also now clear that Mo is not an essential metal for biological nitrogen fixation since nitrogenases based on V and Fe have been isolated. However, the similarities of the structure and function of the three types of nitrogenase strongly suggest that they use a common mechanism for the activation and reduction of N_2.