Abstract: By anaerobical incubation of the Azotobacter vinelandii MoFe protein with O-phenan-throline (O-phen) urea could remarkably enhance the number of Fe atoms chelated from the protein. When excessive Na2S204 was. added, the Fe atoms chelated by O-phen from the MoFe protein increased rapidly. After Sephadex G-25 column chromatography, the metallo-clusters-deficient MoFe protein which lost 85 % of the C2H2 reduction activity was obtained. However, the recovery of protein could be reached over 60 %. After reconstitution with a reconstituent solution containing Mo, the ultraviolet and visible CD spectra, and profile of the native anaerobic gel electrophoresis, and C2H2-reduction activity of the protein were signify cantly restored. The results indicated that: (1) Under anaerobic condition, urea could not only result in the chelation by O-phen of Fe atoms from P-cluster, but also the chelation of Fe atoms from FeMoco in the protein. (2) The valence of Fe atoms in MoFe protein might not be all the same. (3) The structure and function of the severely metalloclusters-deficient MoFe protein could be partially restored by reconstitution with the Mo-containing reconstituent solution.

Key words: Urea, O-phenanthroline, Azotobacter vinelandii, Nitrogenase MoFe prorein, Metallocluster, Reconstituted protein