A thylakoid polypeptide involved in the reconstitution of photosynthetic oxygen evolution

Abstract

Sonication of barley thylakoids in a high salt buffer released three polypeptides of Mr 32,000, 23,000, and 13,500 which were purified to homogeneity by chromatofocusing. Highly purified inside-out photosystem II preparations were obtained by French Press treatment or by Triton X-100 fractionation of stacked lamellar systems. Both preparations are composed of pairs of appressed membrane sheets. In the French Press preparation, the majority of these membrane pairs are sealed whereas they are predominantly unsealed in the Triton X-100 preparation. Both preparations are able to evolve oxygen and show reversed proton pumping. The oxygen evolving capacity and variable fluorescence of both preparations were lost upon washing with high salt buffer. This treatment also removed three polypeptides at Mr 32,000, 23,000, and 13,500. The inactivated preparations were reconstituted with respect to oxygen evolution and variable fluorescence by rebinding of the isolated Mr 23,000 polypeptide. The Mr 32,000 and 13,500 polypeptides had no effect on reconstitution.