Cation Control of Photosystem 2 Electron Donation Reactions

Abstract

The electron donation pathway of photosystem (PS) 2 is arranged to ensure a rapid channeling of oxidising equivalents from the photo-oxidised reaction centre to the oxygen-evolving complex (Renger, Eckert 1980). Whether this is achieved by the two complexes integrated within the same macromolecular unit has, however, been questioned (Lavorel 1976; Diner 1976). Our recent analysis of the electron donation reactions under partial inhibitory conditions indicates that the two complexes may interact via a diffusion-limited step (Packham, Barber 1983). Using inside-out thylakoid vesicles, inwhich the donor pathway is directly accessible to the suspension medium, we have attempted to correlate the inhibition of the oxygen-evolution complex, induced by cation depletion, with changes in the structural organization of PS2.