title: ApoNifH functions in iron-molybdenum cofactor synthesis and apodinitrogenase maturation.
abstract: NifH (dinitrogenase reductase) has three important roles in the nitrogenase enzyme system. In addition to its role as the obligate electron donor to dinitrogenase, NifH is required for the iron-molybdenum cofactor (FeMo-co) synthesis and apodinitrogenase maturation. We have investigated the requirement of the Fe-S cluster of NifH for these processes by preparing apoNifH. The 4Fe-4S cluster of NifH was removed by chelation of the cluster with alpha, alpha'-bipyridyl. The resulting apoNifH was tested in in vitro FeMo-co synthesis and apodinitrogenase maturation reactions and was found to function in both these processes. Thus, the presence of a redox active 4Fe-4S cluster in NifH is not required for its function in FeMo-co synthesis and in apodinitrogenase maturation. This, in turn, implies that the role of NifH in these processes is not one of electron transfer or of iron or sulfur donation.
authors.affiliation: Department of Biochemistry and Center for the Study of Nitrogen Fixation, College of Agricultural and Life Sciences, University of Wisconsin, Madison, WI 53706, USA.
authors.forename: P
authors.initials: P
authors.lastname: Rangaraj
authors.forename: V K
authors.initials: VK
authors.lastname: Shah
authors.forename: P W
authors.initials: PW
authors.lastname: Ludden
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000693:Anaerobiosis; D001051:Apoenzymes / Q000378:metabolism*; D016948:Azotobacter vinelandii / Q000201:enzymology*; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000302:isolation & purification / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000378:metabolism; D007700:Kinetics; D046911:Macromolecular Substances; D008983:Molybdoferredoxin / Q000096:biosynthesis*; D009591:Nitrogenase / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D010088:Oxidoreductases
chemical_list: D001051:Apoenzymes; D004792:Enzyme Precursors; D007506:Iron-Sulfur Proteins; D046911:Macromolecular Substances; D008983:Molybdoferredoxin; D000255:Adenosine Triphosphate; D010088:Oxidoreductases; D009591:Nitrogenase; C029130:nitrogenase reductase