 Electron transfer by FNR is a rate limiting step in photosynthesis, so the plastidic FNR in plants have evolved to be highly efficient.These plastidic FNRs are 20–100 fold more active than bacterial FNRs.This higher catalytic efficiency of the transfer of electrons from FAD to NADP is related to structural changes in the active site that reduce the distance between the N5 in FAD and the C4 in NADP.