Electron paramagnetic resonance and light absorption studies on c-type cytochromes of the anaerobic sulfate reducer Desulfovibrio

1. 1. EPR and optical studies provide for differentiation of the c-type cytochromes examined into three groups with different heme contents. The three groups consist of: the mono-heme type, cytochrome c-553; cytochromes c3 and c′3 containing at least two hemes per molecule; and cytochromes cc3 and cc′3 which contain at least four hemes per molecule. This division into three groups agrees with a previous similar grouping based on amino acid composition and/or sequence. 2. 2. EPR studies suggest that heme-heme interaction is manifest in the ferric state of cytochrome c3. At about a half-reduced state, an EPR-detectable intermediate with a decreased degree of interaction between hemes is observed. 3. 3. Based on EPR and light absorption changes, cytochrome c3 is extremely stable in 8 M urea in the ferric state. However, repeated reduction and reoxidation in the presence of 8 M urea results in the apparent conversion of the multi-heme system to a mono-heme system. 4. 4. These and other observations suggest a conformation change involving a possible reorientation of the multi-heme moieties in the partially or fully-reduced tate. Depending on the reactant(s) present this process may be reversible.