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The first information about vibrational modes of the Fe-S clusters in nitrogenase, using the technique of nuclear resonance vibrational spectroscopy (NRVS) is reported. The vibrational spectra derived from NRVS experiments support the presence of an interstitial atom in both isolated FeMoCo and in the Azotobacter vinelandii protein (Avl)-bound FeMo-cofactor.

The Fe(S(sub cys))4 site in reduced and oxidized rubredoxin (Rd) from Pyrococcus furiosus (Pf) is studied using (super 57)Fe nuclear resonance vibrational spectroscopy (NRVS). A normal mode analysis using a Urey-Bradley force field is undertaken to quantitatively interpret the NRVS spectra and to set the stage for analysis of seemingly more complex problems such as hydrogenase and nitrogenase.

Nuclear resonant inelastic X-ray scatting (NRIXS) data on FeS4 and FeH(D)(sub 6) model systems is presented. Fe-H stretches have high frequencies and little Fe motion and both factors will reduce NIRXS intensity.

Nitrogenase catalyzes a reaction critical for life, the reduction of N(2) to 2NH(3), yet we still know relatively little about its catalytic mechanism. We have used the synchrotron technique of (57)Fe nuclear resonance vibrational spectroscopy (NRVS) to study the dynamics of the Fe-S clusters in this enzyme. The catalytic site FeMo-cofactor exhibits a strong signal near 190 cm(-)(1), where conventional Fe-S clusters have weak NRVS. This intensity is ascribed to cluster breathing modes whose frequency is raised by an interstitial atom. A variety of Fe-S stretching modes are also observed between 250 and 400 cm(-)(1). This work is the first spectroscopic information about the vibrational modes of the intact nitrogenase FeMo-cofactor and P-cluster.