Structure and function of photosystem I: interaction with its soluble electron carriers and external antenna systems.

Photosystem I (PS I) is a large membrane protein complex that catalyzes the first step of solar conversion, the light-induced transmembrane electron transfer, and generates reductants for CO2 assimilation. It consists of 12 different proteins and 127 cofactors that perform light capturing and electron transfer. The function of PS I includes inter-protein electron transfer between PS I and smaller soluble electron transfer proteins. The structure of PS I is discussed with respect to the potential docking sites for the soluble electron acceptors, ferredoxin/flavodoxin, at the stromal side and the soluble electron donors, cytochrome c6/plastocyanin, at the luminal side of the PS I complex. Furthermore, the potential interaction sites with the peripheral antenna proteins are discussed.