Photosystem I (PSI) is a multisubunit complex that catalyses the final stage of the light reactions in chloroplasts. Plant photosystem I (PSI) consists of at least 18 different protein subunits and PsaK is a subunit with two transmembrane a-helices, which in cyanobacteria is located at the periphery of the complex. PsaK has a role in organizing the peripheral light-harvesting complexes on the core antenna of photosystem I.
