The thylakoid membrane of Rhodopseudomonas viridis contains extensive, regular arrays of photoreceptor complexes arranged on a hexagonal lattice with a repeat distance of ˜130 Å. Single membrane sheets were obtained by mild treatment of the thylakoid fraction with the detergent Triton X‐100. Heavy metal shadowing and electron microscopy of isolated thylakoids indicated a strong asymmetry of the membrane, showing a smooth plasmic and a rough exoplasmic side. Fourier processing of rotary‐shadowed specimens showed the different surface relief on both sides of the membrane. Structural units on both sides were roughly circular and showed 6‐fold symmetry at a resolution close to 20 Å. The structural unit was characterised by a central core that seemed to extend through the membrane, protruding on the exoplasmic side. The core was surrounded by a ring showing 12 subunits on the plasmic side. Rotary‐shadowed as well as negatively‐stained membranes indicated a handedness of the structure. Treatment of thylakoid vesicles with higher detergent concentrations yielded a fraction of particles showing the same features as Fourier maps of the structural units. The isolated particles therefore appeared to represent structurally intact units of photosynthesis.

The photosynthetic membranes of Rhodopseudomonas viridis consist of a regular array of structural units. Each unit is composed of a central core (thought to contain the reaction centre complex) surrounded by a subdivided ring of protein (of likely antennae function). These individual units can be dissociated from the membrances using a variety of detergent treatments. The absorption spectrum, used as a criterion of a native state, is retained. All of the seven major polypeptides, the four reaction centre polypeptides (cytochrome, H, M and L chain) as well as the three light‐harvesting polypeptides (B1015‐α, β and ξ) are shown to be present. Electron microscopy of the units shows a similar structure to the units within the membrane. surface‐specific iodination of both membranes and units labels predominantly polypeptides H, B1015‐α, and ξ. M and L are weakly labelled. In addition, B1015‐β is labelled in the isolated units. This, with other evidence, supports an allocation of light‐harvesting polypeptides to the outer ring. Further solubilisation of these units separates the reaction centre (as a native complex containing all four polypeptides) from the light‐harvesting polypeptides. The light‐harvesting polypeptides are obtained in a form containing all three polypeptides and bound pigment, however the peak at 1015 nm corresponding to native bacteriochlorophyll b is lost.

No abstract

Hall-effect thrusters (HETs) are among the most commonly used propulsion systems for attitude and orbit control of satellites. As an arrangement in a cluster or individually, equipped with a mechanical suspension, thrust in all three spatial directions can be generated, but requires additional mechanisms and components. Therefore, the Technische Universität Dresden (TU Dresden) is currently working on a concept for developing a Hall-effect thruster with integrated thrust vector control, which would allow steering in all three spatial directions with just a single thruster. This new concept is intended to work solely by influencing the ion beam and should not have any additional mechanical components. The HET will come with a segmented anode to set different electrical potentials at the anode and cause an inhomogeneous distribution of the electric field within the discharge channel, which results in an inhomogeneous force vector distribution at the exit plane. It is assumed that this will generate turning moments around the center of gravity. Deliberately causing those turning moments can therefore be used for steering with just one thruster. This work presents the concept of the propulsion system, gives an outlook on the advantages of its technology and shows capabilities for space applications.