Ferredoxin electron transfer site on cytochrome c3. Structural hypothesis of an intramolecular electron transfer pathway within a tetra‐heme cytochrome

Abstract

To specify electron exchanges involving Desulfovibrio desulfuricans Norway tetra-heme cytochrome c₃, the chemical modification of arginine 73 residue performed. Biochemical and biophysical studies have shown that modified cytochrome retains its ability to both interact and act as an electron carrier with its redox partners, ferredoxin and hydrogenase. Moreover, the chemical modification effects on the cytochrome c₃ ¹H NMR spectrum were similar to that induced by the presence of ferredoxin. This suggests that arginine 73 is localized on the cytochrome c₃ ferredoxin interacting site. The identification of heme 4, the closest heme to arginine 73, as the ferredoxin interacting heme helps us to hypothesize about the role of three other hemes in the molecule. A structural hypothesis for an intramolecular electron transfer pathway, involving hemes 4, 3, and 1, is proposed on th basis of the crystal structures of D. vulgaris Miyazaki and D. desulfuricans Norway cytochromes c₃. The unique of role of some structural features (α helix, aromatic residues) intervening between the heme groups, is proposed.