Photosystem I

This chapter discusseses PS I in detail. Chlamydomonas has been an incredibly powerful and productive platform from which to study PS I. PS I is composed of 14 polypeptides and its core cofactors are explained in depth. Energy transfers within, from PS I and to other cell is also elaborated. After a shift of the mutant to the nonpermissive temperature, PS I remained stable, indicating that the effect was upon assembly. PS I can be thought of as a light-driven electron pump, transferring electrons from plastocyanin (or cytochrome c 6) on the lumenal side to ferredoxin on the stromal side, both across the thylakoid membrane and over an energy barrier. PS I can function as part of the linear or cyclic electron transport pathways. The resemblance of PS I from this organism to that of higher plants also allows the study of questions that would not be easy or possible in either plants or cyanobacteria. These include: the mechanisms by which external antenna proteins attach to the PS I, and how these interactions are regulated; the structural arrangement of these antenna proteins with PS I, and how these relate to pathways of excitation quenching; and the role of specialized membrane domains in the function of PS I.