Nitrogenases iron-only nitrogenase

Molybdenum nitrogenase has been the subject of intensive study for more than 30 years, but much less work has been done on the vanadium and iron-only nitrogenases. Consequently, we first review the properties of Mo nitrogenase, and then in later sections outline what is known of the other two enzymes. 

Schneider, K., Gollan, U., Drottboom, M. et al. Selsemaier-Voight, S. Plass, W. and Muller, A. (1997) Comparative biochemical characterization of the iron-only nitrogenase and the molybdenum nitrogenase from Rhodobacter capsulatus. Eur. J. Biochem., 244, 789-800. 

Also required for the vanadium and iron-only nitrogenases, which are encoded by vnf and anf genes, respectively. 

Figure 12 Assembly of the molybdenum nitrogenase. Pathways of FeMo cofactor biosynthesis, Fe protein maturation, and MoFe protein assembly are indicated in dotted, dashed, and solid arrows, respectively. The nif gene products that are also required for the vanadium and iron-only nitrogenase systems are indicated by ...

The an/H-encoded Fe protein of the iron-only nitrogenase is very homologous to the ni/H-encoded Fe protein of the molybdenum nitrogenase and the vn -encoded Fe protein of the vanadium nitrogenase. This Fe protein also has an ax homodimeric composition and contains a [4Fe-4S] cluster. 

The iron-only nitrogenase has been isolated from A. vinelandii, R. rubum, and R. capsulatus (Table 1). It is also similar to the molybdenum nitrogenase except that the molybdenum is replaced by iron in the protein. It has the molybdenum iron (MoFe) protein equivalent in the iron-iron (FeFe) protein and the iron (Fe) protein equivalent. 

Rrahn, E., Schneider, K. and Muller, A. (1996). Comparative characterization of H2 production by the conventional Mo nitrogenase and the alternative iron-only nitrogenase of Rhodobacter capsulatus hup mutants. Appl. Microbiol. Biotechnol. 46, 285-290. 

The vanadium-nitrogenase and iron-only nitrogenases, also known as alternative nitrogenases, are related to the molybdenum nitrogenase but are all genetically distinct. A fourth and completely different nonconventional type of nitrogenase is known it also contains iron and molybdenum, but couples dinitrogen reduction to the oxidation of superoxide and carbon monoxide ]17]. 

Progress in the biochemistry and spectroscopy of iron-only nitrogenase has occurred, with the most active, pure preparations reported in 1997. Mossbauer and EXAFS results support electronic and structural analogy between the eight-iron cluster in this enzyme (the FeFeco ) and the FeMoco. One notable difference is that the FeFeco is diamagnetic in its dithionite-reduced form, and thus corresponds to M° in the MoFe protein. Therefore, the oxidation states are thought to be Fe(II)4Fe(III)4 or Fe(II)6Fe(III)2, in analogy to the two most likely oxidation... 

Subsequently, the electronic structure of the FeFeco of iron-only nitrogenase was investigated, employing the same methods. The ground state... 

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