Ferredoxin standard redox potential

Figure 3.7. The energy profile of a nitrogenase reaction. Eo is the standard redox potential of the reactants, intermediates and products of the reaction Fd = ferredoxin FeP = Fe protein FeMo = FeMo protein. The arrow indicates the increase of the reduction potential upon ATP hydrolysis (Likhtenshtein 1988a). Reproduced with permission.

The standard redox potential of the Fe-protein is low, and it becomes even lower when it interacts with MgATP. A specific low-potential electron donor channels electrons from the cell s general metabolism to nitrogenase. In the anaerobe Clostridium pasteurianum it was known to be a ferredoxin the UNF s particular contribution in this area was to show, in parallel with workers in the Netherlands, that the equivalent electron donor in A. chroococcum was a flavodoxin, shuttling between its reduced and semi-quinone forms. 

Iron-Sulfur Electron Transfer Proteins.31 Ferredoxins. These relatively small proteins (6,000-12,000) which contain non-heme iron, cysteine-sulfur, and so-called inorganic sulfur have redox potentials close to that of the standard hydrogen electrode. They appear to occur in all green plants, including algae, in all photosynthetic bacteria and protozoa and in some fermentative anaerobic bacteria. These molecules play an essential role as electron-transfer agents at the low-potential end of the photosynthetic process, but an exact chemical specification of their activity is still lacking. 

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