What Determines the Redox Potential of Ferredoxins

For many cytochromes P450 (P450), the electrons are transferred from the reductase to the P450 via a [2Fe-2S] cluster ferredoxin (e.g. putidaredoxin, terpredoxin or adrenodoxin). A similar role is played by several plant-type ferredoxins to transfer electrons from photosystem I to NADP. Other ferredoxins like E. coli ferredoxin are probably involved in the biogenesis of iron-sulfur clusters. To understand what modulates the redox potential of the metal center in the different proteins, we have developed a method to calculate redox potentials from first principles. In calculations for Anabaena PCC7119 ferredoxin, we found that certain changes in protein structure upon a change in redox state have a strong influence on the redox potential. Preliminary results indicate that the same mechanism may be important for determining the redox potentials of other ferredoxins.