Small angle x-ray scattering of the thylakoid membranes of Rhodopseudomonas speroides in aqueous suspensions.

The diffraction patterns of particles which have the shape of hollow spheres, i.e. vesicles, can be satisfactorily analyzed by means of a new formula of Weick (1974). This formula is used for the small angle X-ray scattering analysis of aqueous suspensions of thylakoids of Rhodopseudomonas spheroides. Some essential results are: (a) The membrane has a rather asymmetric structure with one layer of low electron density at its inner side and two layers of high electron density near the outer surface of the thylakoids. (b) The distance of the electron density maxima of the latter two layers is 45 +/- 5 A. (c) Between the two maxima is a region of an electron density nearly equal to that of water. (d) The sequence of the peaks is - + 0 + with increasing radius. The peaks extend over an interval of 120 +/- 10 A. (e) The thylakoids are strikingly of the same size. Their diameters, if defined by the outmost layer, vary statistically by about 4% and have an average value of approximately 640 A.