A general model for regulation of photosynthetic unit function by protein phosphorylation

Abstract

We propose that regulatory effects of membrane protein phosphorylation in photosynthetic systems result in all cases from simultaneous phosphorylation by a single kinase of the polypeptides of two intrinsic pigment-protein complexes, with phosphorylation leading to their mutual electrostatic repulsion in a direction parallel to the membrane plane and therefore to decreased excitation energy transfer between them. One complex is a peripheral light-harvesting complex and the other is bound to the reaction centre and functions as a link in excitation energy transfer. Immediate effects of phosphorylation are therefore decreased absorption cross-section together with decreased cooperativity of photosynthetic units. This general model applies equally to photosystem II of green plants, algae and cyanobacteria, as well as to the single photosystem of purple bacteria. Special cases of this general model permit increased excitation energy transfer to one type of reaction centre at the expense of another, and this may occur even in laterally homogeneous membranes that are uniformly unappressed.