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.

► TpIc3 is a soluble tetrahaem cytochrome from sulphate reducing bacteria.
► 2D NMR exchange was used to quantify intermolecular electron transfer rates.
► Only single-electron transfers were detected in each collisional event.
► The self exchange rate is about 30 times slower than the diffusion limit.
► Electron transfer between TpIc3 and TpIIc3 from D. africanus is diffusion limited.