Electron transfer between multihaem cytochromes c₃ from Desulfovibrio africanus

The tetrahaem type I cytochromes c₃ from Desulfovibrionaceae shuttle electrons from a periplasmic hydrogenase to transmembrane electron transfer complexes. In D. africanus, it is believed that the electrons are received by another tetrahaem cytochrome c₃, denoted type II, which is associated with the membrane complex. Thermodynamic measurements show that the type I cytochrome c₃ has the potential to transfer two electrons at a time. This study uses two-dimensional NMR to investigate the exchange of electrons between type I and type II cytochromes c₃ at equilibrium in intermediate stages of oxidation. The results indicate that the two proteins are physiological partners but that only single-electron transfers occur in solution.