Ferredoxin is a soluble iron sulfur protein in the stroma of the chloroplast that carries electrons in photosystem II. Ferredoxin accepts electrons from the iron-sulfur protein, FB, and passes them to  NADP⁺ in the last step of electron transport. In a sense ferredoxin, rather than NADP⁺, can be considered the direct recipient of electrons from the pathway because reduced ferredoxin is a source of low-potential electrons for many reductive processes, such as the reduction of thioredoxin (for example, see Figure 17.23).

Ferredoxin is used by nitrogenase reductase (component II), an enzyme of nitrogen fixation, and also by nitrite reductase, which catalyzes reduction of nitrite to ammonia