SOME STRUCTURAL AND PHOTOCHEMICAL PROPERTIES OF RHODOPSEUDOMONAS PALUSTRIS SUBCHROMATOPHORE PARTICLES OBTAINED BY TREATMENT WITH TRITON X-100

Treatment of Rhodopseudomonas palustris chromatophores with 0.6% Triton X-100 causes a significant change in the fluorescence spectrum from an emission peak at 895 mμ and a shoulder at 875 mμ to a more symmetrical peak at 867 mμ. This indicates the spatial arrangement of the three bacteriochlorophyll (Bchl) forms has been changed so that energy transfer from the 857-mμ form to the 873-mμ form is prevented. Treatment with 4% Triton produces two fragments separable by sucrose density gradient centrifugation. The heavy fraction is composed of particles which form linear aggregates which are 65-80 Å in thickness and which contain the photochemical apparatus of the chromatophore. This fraction contains the long-wavelength Bchl form which absorbs at 873 mμ, as well as some of the shorter wavelength Bchl absorbing at 802 mμ. This fraction shows a light-induced bleaching (oxidation) of a portion of the 873-mμ Bchl, which represents the reaction center Bchl. Coupled to this is a photoreduction of endogenous ubiquinone. The light fragment produced by Triton shows no definite structure by electron microscopy, contains the 802- and 857-mμ forms of Bchl, and is devoid of the photochemical activities observed for the particulate fraction. It is concluded that the original photosynthetic membrane system contains the 802 and 857 forms of Bchl in the membrane matrix, that these Bchl molecules serve to harvest light energy, and that distributed on this membrane are the small, photochemically competent particles which initiate the photochemical reactions peculiar to bacterial photosynthesis. © 1968, American Chemical Society. All rights reserved.