Reconstitution of H+ translocation and photophosphorylation with photosystem I reaction centers, PMS, and CF“1CF”0

This chapter discusses the reconstitution of H⁺Translocation and photophosphorylation with photosystem I reaction centers, phenazine methosulfate (PMS), and CF₁CF₀. With an appropriate artificial redox system such as PMS in the presence of an inhibitor for electron transport from photosystem II, very high rates of photophosphorylation can be achieved. This partial reaction catalyzed by photosystem I constitutes an artificial chemiosmotic loop, because PMS translocates protons from outside to inside the chloroplast thylakoids during its redox cycle that is driven by the light-induced charge separation across the membrane in the reaction center. Light-induced quench of 9-aminoacridine in the presence of reduced PMS indicates the H⁺uptake into the vesicles. Without the proton pumping by Photosystem I reaction centers (PSI-RC) and PMS, CF₁CF₀liposomes do not catalyze net ATP synthesis, but carry out uncoupler-sensitive ATP/P_iexchange. The chapter outlines the procedures for the preparation of PSI-RC and CF₁CF₀.