Abstract: By treating the MoFe protein of nitrogenase from Azotobacter vinelandii with O-phenan-throline under anaerobic or aerobic condition, inactive MoFe protein which was partially deficient in P-cluster or in both P-cluster and FeMoco could be obtained. The above mentioned inactive MoFe proteins were incubated with a reconstituent solution containing Ma2MoO4, Na2S, dittnothreitol (DTT) and homocitrate or citrate. Results showed that the acetylene and proton reduction activity of nitrogenase could be restored in both treated proteins after incubating with the reconstituent solution containing either citrate or homocitrate, and their metal content, CD and MCD spectra which reflected the content of metal clusters in the MoFe protein could also be restored. But their restoration of the Ns-reduction ability of the treated MoFe proteins was significantly different from each other, the P-cluster deficient MoFe protein could be restored by a reconstituent solution containing either citrate or homocitrate, and the P-cluster pius FeMoco deficient MoFe protein could only be restored bythe reconstituent solution containing homocitrate. The result indicated that the P-cluster assembled by the reconstituent solution containing either citrate or homocitrate was similar to that of the native MoFe protein, and the FeMoco which was assembled only by the reconstituent solution containing homocitrate was similar to that of the native MoFe protein. These results further demonstrated that homocitrate is an essential component of FeMoco.

Key words: Homocitrate, FeMoco, Nitrogenase MoFe protein, Azotobacter vinelandii