Structure and function of ferredoxin–NADP+ reductase. (A) Structure of ferredoxin–NADP+ reductase. This enzyme accepts electrons, one at a time, from ferredoxin (shown in orange). (B) Ferredoxin–NADP+ reductase first accepts two electrons, generated by photosystem I, and two protons from the lumen to form two molecules of reduced ferredoxin (Fd). Reduced ferredoxin is then used to form FADH2, which then transfers two electrons and a proton to NADP+ to form NADPH in the stroma.
[Drawn from 1EWY.pdb.]