A four-iron ferredoxin from Desulfovibrio desulfuricans.

Ferredoxin from Desulfovibrio desulfuricans was isolated, purified and crystallized. It contains four iron atoms and four sulphido or ;acid-labile' sulphur atoms for a molecule of 6000 daltons. The absorption spectrum in the u.v.-visible region and the electron-paramagnetic-resonance signals of the reduced protein are similar to those observed for other four-iron ferredoxins. The amino acid composition is different from that of Desulfovibrio gigas ferredoxin. The redox potential of -0.33V at pH7.0 was determined by dye techniques.