Topography of Photosystem II Reaction Center Components in Thylakoid Membranes

The main function of photosynthesis, i.e. conversion of solar energy into electrochemical one, occurs in the pigment-protein-lipid complexes of the reaction centers (RC’s) immersed into thin (∼50A) phospholipid thylakoid membranes [1,2]. The thylakoid membranes also contain a light harvesting chlorophyll and other auxiliary pigments. When the light is absorbed by photosystem II (PS II), the charges in the RC are photoche-mically separated between a singletically excited chlorophyll molecule P680 and pheophytin (Pheo). Further, the electron is transferred to a “stable” acceptor QA (a complex of plastoquinone with iron [1,2]) [2]. The electron hole appearing in the cation-radical P680+· is filled by the electron removed from a water molecule. This finally results in O2 evolution.