Spectroscopic properties of the CP43 core antenna protein of photosystem II

CP43 is a chlorophyll-protein complex that funnels excitation energy from t he main light-harvesting system of photosystem II to the photochemical reac tion center. We purified CP43 from spinach photosystem II membranes in the presence of the nonionic detergent n-dodecyl-beta,D-maltoside and recorded its spectroscopic properties at various temperatures between 4 and 293 K by a number of polarized absorption and fluorescence techniques, fluorescence line narrowing, and Stark spectroscopy. The results indicate two "red" sta tes in the Q(y) absorption region of the chlorophylls. The first peaks at 6 82.5 nm at 4 K, has an extremely narrow bandwidth with a full width at half -maximum of similar to 2.7 nm (58 cm(-1)) at 4 K, and has the oscillator st rength of a single chlorophyll. The second peaks at similar to 679 nm, has a much broader bandshape, is caused by several excitonically interacting ch lorophylls, and is responsible for all 4 K absorption at wavelengths longer than 685 nm. The Stark spectrum of CP43 resembles the first derivative of the absorption spectrum and has an exceptionally small overall size, which we attribute to opposing orientations of the monomer dipole moments of the excitonically coupled pigments.