Conformational properties of multihemic cytochromes c from Desulfuromonas acetoxidans

In the classification of c-type cytochromes, the class III includes multihemic cytochromes c with low redox potential constituting the cytochrome c3 superfamily. Most of the cytochromes described have been isolated from sulfate or sulfur reducing bacteria. We report here the comparison between two multihemic cytochromes, the newly characterized 50 kDa cytochrome from Desulfuromonas acetoxidans and the cytochrome c7 from the same strain in order to contribute to understanding the relationships between members of this superfamily. The thermostability of these cytochromes was studied by circular dichroism (CD) and differential scanning calorimetry (DSC). The influence of the temperature on the redox potential was also investigated. The data clearly indicate the presence of two domains in 50 kDa cytochrome and a drastic loss of stability of cytochrome c7 in comparison to cytochrome c3. The results are discussed in the light of the structural properties of the cytochrome c3 superfamily and two sub-groups in this family are proposed.