FE AND MO EXAFS OF AZOTOBACTER-VINELANDII NITROGENASE IN PARTIALLY OXIDIZED AND SINGLY REDUCED FORMS

Fe and Mo K-edge EXAFS spectra of the nitrogenase MoFe protein in the indigo disulfonate (IDS) oxidized form and under slow turnover conditi ons have been recorded. The EXAFS of the one-electron reduced form E(1 ) was obtained as a difference spectrum between the slow turnover and resting (Eo) spectra. Average Fe-S, Fe-Fe, and Fe-Mo distances of 2.33 , 2.60, and 2.66 Angstrom, respectively, along with a second Fe-Fe dis tance at 3.72 Angstrom were found for E(1). The IDS-oxidized MoFe prot ein contains partially oxidized ''P-clusters''. For this sample, avera ge Fe-S, Fe-Fe, and Fe-Mo interactions at 2.31, 2.65, and 2.71 Angstro m, respectively, were found along with the long Fe-Fe interaction at 3 .74 Angstrom. Combination of the current results with previous data on resting and thionin-oxidized nitrogenase shows a general trend--a sig nificant number of the metal-metal distances tend to contract as the e nzyme becomes more reduced.