APONIFH FUNCTIONS IN IRON-MOLYBDENUM COFACTOR SYNTHESIS AND APODINITROGENASE MATURATION

NifH (dinitrogenase reductase) has three important roles in the nitrog enase enzyme system, In addition to its role as the obligate electron donor to dinitrogenase, NifH is required for the iron-molybdenum cofac tor (FeMo-co) synthesis and apodinitrogenase maturation. We have inves tigated the requirement of the Fe-S cluster of NifH for these processe s by preparing apoNifH. The 4Fe-4S cluster of NifH was removed by chel ation of the cluster with (alpha, alpha'-bipyridyl. The resulting apoN ifH was tested in in vitro FeMo-co synthesis and apodinitrogenase matu ration reactions and was Pound to function in both these processes. Th us, the presence of a redox active 4Fe-4S cluster in NifH is not requi red for its function in FeMo-co synthesis and in apodinitrogenase matu ration. This, in turn, implies that the role of NifH in these processe s is not one of electron transfer or of iron or sulfur donation.