Isolation and Partial Characterization of a Manganese and Chloride Binding Protein Present in Highly Purified Photosystem II Complexes of the Thermo philic Cyanobacterium Synechococcus sp.: The Protein Being Detected by Its L -Arginine Metabolizing Activity

Photosystem II complexes were solubilized with the detergent sulfobetaine 12 from thylakoid membranes of the thermophilic cyanobacterium Synechococcus sp. and purified by two sucrose gradient centrifugations and by chromatography on a Mono Q column. In such pho­ tosystem II complexes having a photosynthetic O, evolving activity of 2938 |amol 0 2 evolved/ 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 structure is formed in addition especially under aerobic conditions. This activi­ ty remained associated with photosystem II complexes even after substantial additional treat­ ments to remove loosely bound proteins. On chlorophyll basis the maximal activity obtained under optimal assay conditions corresponded to 94 (miol ornithine formed/mg chloro­ phyll x h. This PS II associated, L-arginine metabolizing enzyme was isolated (utilizing a man­ ganese charged chelating Sepharose 6 B column) and partially characterized. It could be shown that this enzyme requires manganese and chloride for its L-arginine metabolizing activity and that 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 proteins 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 pro­ vided a suitable assay for its isolation from photosystem II complexes, has any physiological significance, can not be answered at the present time.