Disintegration of Rhodospirillum rubrum chromatophore membrane into photoreaction units, reaction centers, and ubiquinone-10 protein with mixture of cholate and deoxycholate

Abstract

1. The membrane of Rhodospirillum rubrum chromatophores was disintegrated with mild detergents (cholate and deoxycholate) in order to study the spatial arrangement of the functional proteins in the photochemical apparatus and the electron transport system in the membrane. 2. The components solubilized from the membrane by a mixture of cholate and deoxycholate (C-DOC) were separated into four fractions by molecular-sieve chromatography in the presence of C-DOC; they were designated as F1, F2, F3, and F4 in the order of elution. The fractions were further purified by repeated molecular-sieve chromatography in the presence of C-DOC until each fraction was chromatographically homogeneous. 3. F1 appeared to be conjugated forms of F2. 4. The purified F2 was composed of a rigid complex having a weight of 7 X 10(5) daltons, containing approximately 10 different kinds of protein species with molecular weights of 3.8 X 10(4), 3.6 X 10(4), 3.5 X 10(4), 2.8 X 10(4), 2.7 X 10(4), 2.6 X 10(4), 1.3 X 10(4), 1.2 X 10(4), 1.1 X 10(4), and 1.0 X 10(4). The complex contained 33 bacteriochlorophylls, 4 iron atoms, and 90 phosphates, but no cytochrome, ubiquinone, or phospholipid. It showed the same reaction center activity as chromatophores, indicating that the complex was a unit of the photochemical apparatus (photoreaction unit). Each chromatophore of average size was estimated to possess about 24 photoreaction units. 5. The purified F3 showed an absorbance spectrum characteristic of reaction centers, and contained 3.4 bacteriochlorophylls, 2.0 bacteriopheophytins, and 1.9 acid-labile iron atoms, but no cytochrome or ubiquinone (C-DOC reaction center). It had a weight of 1.2 X 10(5) daltons, and the main components were 4 protein species with molecular weights of 2.8 X 10(4), 2.7 X 10(4), 2.6 X 10(4), and 1.0 X 10(4). 6. The purified F4 showed a molecular weight of about 11,000, and contained one mole of ubiquinone-10 per mole (ubiquinone-10 protein). 7. The reaction center activity of C-DOC reaction centers was stimulated by ubiquinone-10 protein. In addition, the reaction center oxidized reduced cytochrome c2 in the light, provided that ubiquinone-10 protein was present (photo-oxidase activity).