Broad-band quasi-optical HF-EPR spectroscopy: Application to the study of the ferrous iron center from a rubredoxin mutant

High-frequency electron paramagnetic resonance (HF-EPR) allows obtaining detailed information on the anisotropy of integer-spin systems, which are usually silent at conventional EPR frequencies (X- or Q-bands). However, the studies performed so far on integer-spin systems have mostly dealt with synthetic complexes. In this paper, we present first results obtained on a mono-nuclear high-spin ferrous iron center of a rubredoxin-type protein. This study shows that the broad-band quasi-optical technique of HF-EPR is a suitable approach towards the study of biologically relevant metal centers with large zero-field splittings.