ORGANIZATION OF THE O2-EVOLUTION ENZYME COMPLEX IN A HIGHLY ACTIVE O2-EVOLVING PHOTOSYSTEM-II PREPARATION

Abstract

This chapter discusses the organization of the O2-evolution enzyme complex in a highly active O2-evolving photosystem-II (PS-II) preparation. O2 evolution in chloroplast is believed to be catalyzed by an enzyme complex containing manganese (Mn) at its catalytic site. In a study discussed in the chapter, a highly active O2-evolving PS-II preparation was first isolated from the membranes of a thermophilic blue–green alga Phormidium laminosum, by treatment with laurylamine oxide followed by a Sepharose 6B column chromatography. As the O2-evolution enzyme system of chloroplasts from higher plants seems to be not stable enough to withstand the relatively strong detergent treatment and long preparation procedure, low concentrations of digitonin and Triton X-100 was used for the isolation of a highly active O2-evolving PS-II preparation from spinach chloroplasts. The results suggest that the 33-, 24-, and 18-kDa polypeptides, and two Mn atoms are involved in the O2-evolution system. They are probably located on the outer side of the membrane vesicles on the PS-II preparation and released from the membranes by treatments that inhibit O2 evolution specifically. However, the extent of the release of the three polypeptides and Mn varied depending on the treatment employed.