Structure of a bacterial photosynthetic membrane.

The internal photosynthetic membranes of a photosynthetic bacterium, Rhodopseudomonas viridis, have been studied with a variety of electron microscope techniques. The membranes are composed of a sheet of apparently identical subunits arranged in a hexagonal fashion. The individual subunits repeat at a distance of 110 A. Optical transforms have been used to enhance micrographs of this ordered membrane, and the images synthesized in this way show details of each subunit. The individual subunits are asymmetric, differing slightly in appearance at the outer and inner surfaces of the membrane, and these surface patterns seem to be combined in the image of the thylakoid membrane in negative stain. These studies fix a maximum size for the photosynthetic unit of R. viridis and suggest the suitability of this membrane for further diffraction analysis.