Second protein complex in photosynthetic light reactions
Light-dependent reactions of photosynthesis at the thylakoid membrane
Location of the psa genes in the chloroplast genome of Arabidopsis thaliana . The 21 protein-coding genes involved in photosynthesis are displayed as green boxes.
Photosystem I (PSI , or plastocyanin–ferredoxin oxidoreductase ) is one of two photosystems in the photosynthetic light reactions of algae , plants , and cyanobacteria . Photosystem I [ 1] is an integral membrane protein complex that uses light energy to catalyze the transfer of electrons across the thylakoid membrane from plastocyanin to ferredoxin . Ultimately, the electrons that are transferred by Photosystem I are used to produce the moderate-energy hydrogen carrier NADPH .[ 2] The photon energy absorbed by Photosystem I also produces a proton-motive force that is used to generate ATP . PSI is composed of more than 110 cofactors , significantly more than Photosystem II .[ 3]