ISOLATION AND PARTIAL CHARACTERIZATION OF A MANGANESE AND CHLORIDE BINDING-PROTEIN PRESENT IN HIGHLY PURIFIED PHOTOSYSTEM-II COMPLEXES OF THE THERMOPHILIC CYANOBACTERIUM SYNECHOCOCCUS SP - THE PROTEIN BEING DETECTED BY ITS L-ARGININE METABOLIZING ACTIVITY

Photosystem II complexes were solubilized with the detergent sulfobeta ine 12 from thylakoid membranes of the thermophilic cyanobacterium Syn echococcus sp. and purified by two sucrose gradient centrifugations an d by chromatography on a Mono Q column. In such photosystem II complex es having a photosynthetic O-2 evolving activity of 2938 mu mol O-2 ev olved/mg chlorophyll, x h, an L-arginine metabolizing activity leading to ornithine and urea as major products, could be shown to be present . Besides ornithine and urea, a product (or products) of yet unknown s tructure is formed in addition - especially under aerobic conditions. This activity remained associated with photosystem II complexes even a fter substantial additional treatments to remove loosely bound protein s. On chlorophyll basis the maximal activity obtained under optimal as say conditions corresponded to 94 mu mol ornithine formed/mg chlorophy ll x h. This PS II associated, L-arginine metabolizing enzyme was isol ated (utilizing a manganese charged chelating Sepharose 6 B column) an d partially characterized. It could be shown that this enzyme requires manganese and chloride for its L-arginine metabolizing activity and t hat manganese becomes totally lost during purification indicating that manganese is bound to a fairly exposed site on the protein. Since it is rather unlikely that two different manganese and chloride binding p roteins are present in such highly purified photosystem II complexes, the possibility of this protein being the water oxidizing enzyme will be discussed. Whether the manganese and chloride requiring L-arginine metabolizing activity of this protein which provided a suitable assay for its isolation from photosystem II complexes, has any physiological significance, can not be answered at the present time.