Editing Photosystem I (section)

{{Short description|Second protein complex in photosynthetic light reactions}}
{{Redirect|PS I|other uses|PSI (disambiguation)|PS1|PlayStation 1}}
[[Image:Thylakoid membrane 3.svg|thumb|400px|right|Light-dependent reactions of photosynthesis at the thylakoid membrane]]
{{Infobox enzyme
| Name       = Photosystem I
| EC_number  = 1.97.1.12
| CAS_number =
| GO_code    = 
| image      = File:PSI+LHC.png
| width      = 
| caption    = Plant photosystem&nbsp;I with LHC I 
}}
[[File:Plastomap of Arabidopsis thaliana.svg|thumb|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&nbsp;I''' ('''PSI''', or '''plastocyanin–ferredoxin oxidoreductase''') is one of two [[photosystem]]s in the [[Light-dependent reactions|photosynthetic light reactions]] of [[algae]], [[plant]]s, and [[cyanobacteria]]. [[Photosystem]]&nbsp;I <ref name="pmid3333014">{{cite journal | vauthors = Golbeck JH | title = Structure, function and organization of the Photosystem I reaction center complex | journal = Biochimica et Biophysica Acta (BBA) - Reviews on Bioenergetics | volume = 895 | issue = 3 | pages = 167–204 | year = 1987 | pmid = 3333014 | doi = 10.1016/s0304-4173(87)80002-2 }}</ref> is an [[integral membrane protein]] [[Protein complex|complex]] that uses [[light]] [[energy]] to catalyze the [[electron transfer|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]].<ref>{{cite journal | vauthors = Yamori W, Shikanai T | title = Physiological Functions of Cyclic Electron Transport Around Photosystem I in Sustaining Photosynthesis and Plant Growth | journal = Annual Review of Plant Biology | volume = 67 | pages = 81–106 | date = April 2016 | pmid = 26927905 | doi = 10.1146/annurev-arplant-043015-112002 | doi-access = free }}</ref> The photon energy absorbed by Photosystem I also produces a [[Chemiosmosis|proton-motive force]] that is used to generate [[adenosine triphosphate|ATP]]. PSI is composed of more than 110 [[Cofactor (biochemistry)|cofactor]]s, significantly more than [[Photosystem II]].<ref name="Nelson_2006">{{cite journal | vauthors = Nelson N, Yocum CF | title = Structure and function of photosystems I and II | journal = Annual Review of Plant Biology | volume = 57 | pages = 521–65 | year = 2006 | pmid = 16669773 | doi = 10.1146/annurev.arplant.57.032905.105350 }}</ref>