During photosynthesis, natural electron acceptor NADP is reduced to NADPH in chloroplasts. The following equilibrium reaction takes place.
A reduction reaction that stores energy as NADPH:
: (Reduction)
An oxidation reaction as NADPH's energy is used elsewhere:
: (Oxidation)
Ferredoxin, also known as an NADP+ reductase, is an enzyme that catalyzes the reduction reaction. It is easy to oxidize NADPH but difficult to reduce NADP, hence a catalyst is beneficial. Cytochromes are conjugate proteins that contain a haem group. The iron atom from this group undergoes redox reactions:
: (Reduction)
: (Oxidation)
The light-dependent redox reaction takes place before the light-independent reaction in photosynthesis.