FeFe protein

The VFe protein also has the equivalent of P-cluster pairs which have similar properties to those found in the MoFe protein (159). No information is available on whether P-cluster pairs exist in the FeFe protein, but because of the relatively high sequence identity and the similar genetic basis of its biosynthesis, the occurrence seems highly likely. The catalytic role assigned to the P-cluster pair involves accepting electrons from the Fe protein for storage and future deUvery to the substrate via the FeMo-cofactor centers. As of this writing (ca early 1995), this role has yet to be proved. 

An Fe-only nitrogenase has also been isolated from a nifH mutant of Rhodospirillum rubrum and was characterized as an a2/82<% hex-amer containing only iron, no molybdenum or vanadium, with an o 2Fe4S4-containing Fe protein. A factor could be extracted from the FeFe protein into NMF that combined with apo-MoFe protein to form an active enzyme 193). 

Gollan, U., Schneider, K., Muller, A., Schuddekopf, K., and Klipp, W. 1993. Detection of the in vivo incorporation of a metal cluster into a protein. The FeMo cofactor is inserted into the FeFe protein of the alternative nitrogenase in Rhodobacter capsulatus. Eur. J. Biochem. 215, 25-35. 

Tablet Comparison of the catalytic and biophysical properties of MoFe, VFe, and FeFe proteins ...

Recent EPR, Mossbauer, and EXAFS studies of the FeFe protein from R. capsulatus have provided spectroscopic evidence that the metal clusters of the FeFe protein bear a certain degree of structural homology to those present in the MoFe and VFe proteins. Therefore, it is likely that the FeFe protein contains redox centers that are homologous to the P cluster and FeMo or FeVa cofactor, respectively. The FeMo or FeVa cofactor homologue in the FeFe protein is termed FeFe cofactor or FeFeco. 

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. 

As shown in Table 1, like the VFe protein, the FeFe protein has an axfixh hexameric subunit composition under optimal conditions. The a, fi and 5 subunits of the FeFe protein are encoded by anfD, anfK, and anfG, respectively. Earlier efforts to purify the FeFe protein suffered from low activities, though progress has been made and recent preparations of the FeFe protein from R. capsulatus have activities comparable to that of the VFe protein and do not contain molybdenum or vanadium but high levels of iron (Table 1). 

Iron nitrogenase. FeFe proteins (e.g. from Azotobacter vinelandii and Rhodopseudomonas capsulatus) are hexameric (02 2 2) actually contain low... 

A second iron metalloprotein that is larger (about 220.000 Daltons) and also eventually contains another transition metal that is different for the three kinds of nitrogenase enzymes Mo (MoFe protein), V (VFe protein) or Fe (FeFe protein). It is the MoFe protein that is tiie best known. It contains ... 

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