The Low Molecular Mass Subunits in Higher Plant Photosystem I

Abstract

Photosystem I (PS I) in plants contains 18 different protein subunits. Only three subunits are directly involved in electron transport, while the remaining subunits have a multitude of other functions. Although the PS I complex in plants shows many specific adaptations, it is fascinating that the overall structure and function has been extremely well conserved through the billion years of evolution that separates plants and cyanobacteria. Important roles of the small accessory subunits include efficient docking of the electron donor plastocyanin and the electron acceptor ferredoxin. These functions are conserved between plants and cyanobacteria but plant PS I has a number of specific adaptations, particularly the PS I-N subunit, which is only present in eukaryotes and is involved in the efficient oxidation of plastocyanin.