Electrochemical study of a reconstituted photosynthetic electron-transfer chain

A multi-enzyme electron-transfer chain involving solubilized photosystem I (PSI) as photocatalytic unit, cytochrome eg and ferredoxin as electron carriers and ferredoxin/NADPH oxidoreductase (FNR) as electron acceptor was reconstituted in an electrochemical cell and studied by cyclic voltammetry. The working gold electrodes were modified to react selectively with cytochrome c 6 . Quantitative analysis of the photocatalytic current under continuous illumination allowed the determination of the values k on and k off for the ferredoxin/PSI interaction. An efficient recycling system for NADPH was established, and the dissociation constant of the oxidized ferredoxin/semiquinone FNR complex was extracted by modeling the catalytic efficiency of the chain as a function of ferredoxin concentration. The value determined hereby is consistent with a shift of -50 to -100 mV of the reduction potential of ferredoxin when complexed with FNR.