Resonance Raman Spectra of Spinach Ferredoxin and Adrenodoxin and of Analogue Complexes

Resonance Raman spectra of oxidized spinach ferredoxin and adrenodoxin show six and seven bands in the Fe-S stretching region (280-430 cm** minus **1). Reconstitution of the proteins with labile **3**4S using rhodanese and **3**4SSO//3**2** minus produced isotope shifts allowing identification of all four Fe//2S//2 bridging modes and two (three for adrenodoxin) of the four expected Fe-S(Cys) terminal modes. Similar spectra are observed for the analogue complexes Fe//2S//2(S//2-o-xyl)//2**2** minus (S//2-o-xyl equals o-xylylenedithiolate) and Fe//2S//2Cl//4**2** minus , but they show the expected D//2//h selection rules, and IR-active modes are absent or weak in the Raman spectra. All eight (bridging plus terminal) stretching modes were located via IR as well as Raman spectroscopy and were calculated with reasonable accuracy by using a Urey-Bradley force field scaled to the crystallographically determined interatomic distances.