X-ray diffraction studies on chromatophore membrane from photosynthetic bacteria. I. Diffraction pattern of the photoreaction unit isolated from Rhodospirillum rubrum chromatophore and some characteristics of the structure

Abstract

The X-ray diffraction pattern from chromatophore membranes of a photosynthetic bacterium, Rhodospirillum rubrum, indicates that a highly organized protein assembly exists in the membrane. The X-ray scatterer was solubilized from chromatophores by a mixture of cholate and deoxycholate. The basic component was identified as the photoreaction unit, which consists of light-harvesting bacteriochlorophyll proteins and a reaction center. The radial autocorrelation function, calculated directly from the X-ray intensity dats, made it possible to deduce certain structural features of the X-ray scatterer. 1. The maximum dimension of the X-ray scatterer is estimated to be 110-130 A. 2. The arrangement of the units in the chromatophore membrane is random. 3. Protein molecules in the unit form a rigid structure, being arranged mutually in fixed positions to give a distinct X-ray diffraction pattern. 4. The most probable structure is one which has rotational symmetry.