Chemical modification of carboxyl groups on spinach ferredoxin alters its ability to interact with ferredoxin:NADP reductase.

Treatment of spinach ferredoxin with glycine ethyl ester in the presence of a water soluble carbodiimide resulted in the modification of 3-4 carboxyl groups and decreased the ability of ferredoxin to participate in NADP photoreduction by chloroplast membranes by about 80%. The ability of the modified ferredoxin to receive electrons from the reducing side of Photosystem I was relatively unaffected. These findings suggest that the modified ferredoxin is unable to interact with ferredoxin:NADP reductase. This has been verified by demonstration that the modified ferredoxin fails to produce difference spectra typical of a ferredoxin-ferredoxin:NADP reductase complex when added to ferredoxin:NADP reductase.