Abstract: After the treatment of nitrogenase MoFe protein from Azotobacter vinelandii with O-phenanthroline, ε700nm (molecular extinction coefficient at 700 nm), △ε450nm (molecular circular dichroic extinction coefficient at 450 nm) and the acetylene reduction activity of the treated protein were decreased with the increase in iron atoms chelated from P- cluster of the protein. However, they were restored with the restoration of the metal content after reconstitution of the treated protein with reconstituting solution containing Na2MoO4, ferric citrate, Na2S and dithiothreitol. The results showed that the restoration of the reconstituted protein was resulted from the assembly of new P-cluster in the protein. It seems to be further demonstrated that P-cluster in the MoFe protein is a necessary and important fraction for the protein to reduce substrates.

Key words: O-phenanthroline, Reconstituting solution, P-cluster, Protein reconstitntion, CD, MoFe protein, Azotobacter vinelandii