Photosystem I (PSI) is an integral membrane protein complex that uses light energy to mediate electron transfer from plastocyanin to ferredoxin. Subunit III (or PSI-F) is one of at least 14 different subunits that compose the PSI complex.

1: Subunit III (Psa-F) of photosystem I reaction center of the C4 dicotyledon Flaveria trinervia. Lotan O, Streubel M, Westhoff P, Nechushtai R; Plant Mol Biol 1993;21:573-577. PMID:8443351