The initial steps of biogenesis of cyanobacterial photosystems occur in plasma membranes

During oxygenic photosynthesis in cyanobacteria and chloroplasts of plants and eukaryotic algae, conversion of light energy to biologically useful che mical energy occurs in the specialized thylakoid membranes. Light-induced c harge separation at the reaction centers of photosystems I and II, two mult isubunit pigment-protein complexes in the thylakoid membranes, energeticall y drive sequential photosynthetic electron transfer reactions in this membr ane system. In general, in the prokaryotic cyanobacterial cells, the thylak oid membrane is distinctly different from the plasma membrane. We have rece ntly developed a two-dimensional separation procedure to purify thylakoid a nd plasma membranes from the genetically widely studied cyanobacterium Syne chocystis sp. PCC 6803. Immunoblotting analysis demonstrated that the purif ied plasma membrane contained a number of protein components closely associ ated with the reaction centers of both photosystems. Moreover,these protein s were assembled in the plasma membrane as chlorophyll-containing multiprot ein complexes, as evidenced from nondenaturing green gel and low-temperatur e fluorescence spectroscopy data. Furthermore, electron paramagnetic resona nce spectroscopic analysis showed that in the partially assembled photosyst em I core complex in the plasma membrane, the P700 reaction center was capa ble of undergoing light-induced charge separation. Based on these data, we propose that the plasma membrane, and not the thylakoid membrane, is the si te for a number of the early steps of biogenesis of the photosynthetic reac tion center complexes in these cyanobacterial cells.