Iron-sulphur cluster composition and redox properties of two ferredoxins from Desulfovibrio desulfuricans Norway strain

Two ferredoxins from Desulfovibrio desulfuricans, Norway Strain, were investigated by EPR spectroscopy. Ferredoxin I appears to be a conventional [4Fe-4S]^2+;1+ ferredoxin, with a midpoint reduction potential of ?374 mV at pH 8. Ferredoxin II when reduced, at first showed a more complex spectrum, indicating an interaction between two [4Fe-4S] clusters, and probably, has two clusters per protein subunit. Upon reductive titration ferredoxin II changed to give a spectrum in which no intercluster interaction was seen. The midpoint potentials of the native and modified ferredoxin at pH 8 were estimated to be ?500 and ?440 mV, respectively.