Analysis of Azotobacter vinelandii strains containing defined deletions in nif genes required for FeMo-co biosynthesis
The substrate-reducing site of the MoFe protein of nitrogenase is believed to be a cluster called FeMo-co, which has a stoichiometry Mo:Fe6–8:S8–9:homocitrate (2, 8, 17, 18). It has been known for some time that in vivo. FeMo-co biosynthesis requires the participation of at least the nifO, B, N, E and V gene products (7). In 1984, Ugalde et. al. demonstrated that the biosynthesis of FeMo-co did not require the participation of the nifDK (MoFe protein) polypeptides (19). Subsequent reports, which demonstrated that the Fe protein (nifH) polypeptide was required for FeMo-co biosynthesis in both Klebsiella pneumoniae (6) and A. vinelandii (13), were therefore quite surprising. In the A. vinelandii study we discovered that although FeMo-co was present in a nifDK deletion strain, it was not present in a nifHPK deletion strain. This led us to construct a new A. vinelandii strain, called DJ54, which was deleted only for the nifH structural gene. When derepressed for nitrogenase synthesis this strain contained the MoFe protein polypeptides but did not contain FeMo-co (15).
KeywordsCell Free Extract MoFe Protein Benzene Thiol Wild Type Activity DJ54 Protein
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