A PROTEIN-KINASE IN THE CORE OF PHOTOSYSTEM-II

In green plants, several intrinsic protein components of the photosyst em II (PS II) complexes are subject to reversible phosphorylation on t hreonine residues. Evidence from mutant and inhibitor studies indicate s that multiple kinases are involved. The protein kinases appear to be membrane-bound and redox-regulated, with activity requiring reducing conditions, We report the identification of a protein kinase activity which copurifies with a core complex of PS II and is capable of phosph orylating the photosystem proteins and associated light-harvesting com plex. The enzyme is a distinct and novel protein whose close proximity to the photosystem reaction center is confirmed by its rapid inactiva tion under strong red light irradiation in the presence of oxygen.