A protein kinase in the core of photosystem II.

In green plants, several intrinsic protein components of the photosystem II (PS II) complexes are subject to reversible phosphorylation on threonine residues. Evidence from mutant and inhibitor studies indicates 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 phosphorylating the photosystem proteins and associated light-harvesting complex. The enzyme is a distinct and novel protein whose close proximity to the photosystem reaction center is confirmed by its rapid inactivation under strong red light irradiation in the presence of oxygen.