The resonance Raman (RR) spectra of beef heart aconitase and of an air-stable hydrogenase from Desulfuvibrio desulfuricans, as isolated, are characteristic of 3Fe centers. Activation of aconitase by Fe(II) addition converts the RR spectrum to one characteristic of [4Fe-4S]2+ clusters. Analytical data on aconitase, as isolated, confirms the recent finding (Beinert, H., Emptage, M. H., Dreyer, J.-L., Scott, R. A., Hahn, J. E., Hodgson, K. O., and Thomson, A. J. (1983) Proc. Natl. Acad. Sci. U. S. A. 80, 393-396) of a [3Fe-4S] stoichiometry. The RR spectra of 3Fe centers from aconitase, and the hydrogenase, as well as from several bacterial ferredoxins, conform to the pattern expected for a cube-derived [3Fe-4S] cluster. Perceptible differences are observed among the spectra, which can be explained in terms of differences among the terminal ligands, perhaps limited to their conformations. In the case of aconitase and hydrogenase, frequency shifts suggest additional alterations in the terminal Fe-S bond angles and/or slight differences in core geometry.</p
