Interaction between Ferredoxin and Ferredoxin Nicotinamide Adenine Dinucleotide Phosphate Reductase in Pyridine Nucleotide Photoreduction and Some Partial Reactions

It has been shown by difference spectroscopy that purified ferredoxin and ferredoxin-NADP reductase form a complex. The absorption maxima due to the interaction of the proteins are at 395, 469, and 495 nm. Bleached ferredoxin does not form such a complex. The stoichiometry of the complex is 2 molecules of ferredoxin per 1 molecule of flavoprotein. The complex is decomposed by salts but not by uncharged molecules. Salts at concentrations which cause a decomposition of the complex inhibit the photoreduction of pyridine nucleotides, but do not inhibit electron transport with oxidants which accept electrons prior to the flavoprotein. It is suggested that changes in salt concentration can regulate the photosynthetic electron pathways.