Editing Photosystem I (section)

=== Iron–sulfur complex ===

Three proteinaceous [[Iron–sulfur cluster|iron–sulfur]] reaction centers are found in PSI. Labeled F{{sub|x}}, F{{sub|a}}, and F{{sub|b}}, they serve as electron relays.<ref name="Vassiliev"/> F{{sub|a}} and F{{sub|b}} are bound to [[protein subunit]]s of the PSI complex and F{{sub|x}} is tied to the PSI complex.<ref name="Vassiliev"/> Various experiments have shown some disparity between theories of iron–sulfur cofactor orientation and operation order.<ref name="Vassiliev">{{cite journal | vauthors = Vassiliev IR, Antonkine ML, Golbeck JH | title = Iron-sulfur clusters in type I reaction centers | journal = Biochimica et Biophysica Acta (BBA) - Bioenergetics | volume = 1507 | issue = 1–3 | pages = 139–60 | date = October 2001 | pmid = 11687212 | doi = 10.1016/S0005-2728(01)00197-9 | doi-access =  }}</ref> In one model, F{{sub|x}} passes an electron to F{{sub|a}}, which passes it on to F{{sub|b}} to reach the ferredoxin.<ref name=Grotjohann/>