Interpretation of the Mossbauer Spectra of the Four-Iron Ferredoxin from Bacillus stearothermophilus

Abstract

The Moessbauer spectra of both oxidized and reduced ferrodoxin from B. stearothermophilus were analyzed using computer fits to theoretical spectra obtained from a spin Hamiltonian. A consistent set of parameters was obtained from fits to spectra obtained over a wide range of temperature and magnetic field. These results are interpreted in terms of a model for the active center which is consistent with its electronic and magnetic properties in both redox states. In the model for the oxidized center all 4 Fe atoms have essentially the same valence, intermediate between ferric and ferrous, with one pair spin-up and the other pair spin-down. On reduction the extra electron goes predominantly to 1 pair of Fe atoms which become ferrous with the other pair remaining substantially unchanged. Using this model it is possible to obtain relationships between the spin Hamiltonian parameters for individual Fe atoms and those for the coupled center. This can give further insight into the relation between the observed EPR and Moessbauer spectra.