Origin of the Extreme Longwave Chlorophyll Form of the Photosystem I Trimeric Complex of Spirulina

In contrast to higher plants, cyanobacteria have no light-harvesting complex (LHC) containing chlorophyll (Chl), and whole Chl in cyanobacterial membranes is localized in core complexes of photosystem I (PSI) and PSII [1]. Cyanobacteria are highly enriched with PSI (PSI/PSII ratio is about 5-10); PSI complex in cyanobacteria is organized as monomer and trimer [2,3]. The antenna size (Ch1/P700) of both complexes is about 100 indicating that each monomeric subunit within the trimer contains P700. The equilibrium between PSI trimeric and monomeric complexes in isolated membranes is regulated by changing of electrostatic interaction at various salt conditions [4].