Role of the MoFe Protein ß-95-Cysteinyl Residue in Nitrogenase Catalysis in Azotobacter vinelandii
In order to characterize its catalytic features, the ß-95Asp MoFe protein was purified from mutant strain DJ1096. It has significantly reduced H+ reduction, C2H2-reduction and N2-reduction activity. It was found that a higher percentage of electron flux goes to H+ compared to the wild type MoFe protein. It was also found that reductant independent ATP hydrolysis occurs during H+ reduction, suggesting that the altered MoFe protein has an increased affinity for Fe protein-ADP complex. Surprisingly, CO has a significant enhancement effect on H+ reduction at low electron flux, but not at high electron flux, and highly couples the electron transfer to ATP hydrolysis. These results indicate that the binding of CO to the MoFe protein may either decrease the affinity of Fe-ADP complex for the ß-95Asp MoFe protein or facilitate electron acceptance by the P cluster, thus improving the electron transfer to substrate.
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