Inhibition of iron-molybdenum cofactor biosynthesis by L127Δ NifH and evidence for a complex formation between L127Δ NifH and NifNE

Besides serving as the obligate electron donor to dinitrogenase during nitrogenase turnover, dinitrogenase reductase (NifH) is required for the biosynthesis of the iron-molybdenum cofactor (FeMo-co) and for the maturation of alpha(2)beta(2) apo-dinitrogenase (apo-dinitrogenase maturation). In an attempt to understand the role of NifH in FeMo-co biosynthesis, a site-specific altered form of NifH in which leucine at position 127 has been deleted, L127 Delta, was employed in in vitro FeMo-co synthesis assays, This altered form of NifH has been shown to inhibit substrate reduction by the wild-type nitrogenase complex, forming a tight protein complex with dinitrogenase. The L127 Delta NifH was found to inhibit in vitro FeMo-co synthesis by wild-type NifH as detected by the gamma gel shift assay, Increasing the concentration of NifNE and NifB-cofactor (NifB-co) relieved the inhibition of FeMo-co synthesis by L127 Delta NifH. The formation of a complex of L127 Delta NifH with NifNE was investigated by gel filtration chromatography, We herein report the formation of a complex between L127 Delta NifH and NifNE in the presence of NifB-co, This work presents evidence for one of the possible roles for NifH in FeMo-co biosynthesis, Le. the interaction of NifH with a NifNE.NifB-co complex.