ISOLATION AND SPECTROSCOPIC CHARACTERIZATION OF A PLANTLIKE PHOTOSYSTEM-II REACTION-CENTER FROM THE CYANOBACTERIUM SYNECHOCYSTIS SP-6803

A chlorophyll-protein complex has been isolated from the cyanobacteriu m Synechocystis sp. PCC 6803 that closely resembles higher plant photo system II reaction centers in spectral properties. The Synechocystis c omplex has a pigment content of 5-7 chlorophyll a molecules:1 Cyt b559 :2 pheophytins; an optical absorption redmost transition at similar to 675 nm; and a nonconservative circular dichroism red signal, with ext rema at 682 (+) and 652 (-) nm. Upon illumination, the Synechocystis D 1/D2/Cyt b559 complex accumulates reduced pheophytin. LDS-PAGE and/or immunoblotting showed the D1, D2, and Cyt b559 proteins, aggregated an d degraded forms of D1 and possibly D2, and traces of ATP synthase and the CP47 photosystem II chlorophyll protein. The availability of such a Synechocystis preparation opens the way for employing site-directed mutagenesis in studying primary reactions of oxygenic photosynthesis.