Supramolecular organization of the photosynthetic apparatus of Rhodobacter sphaeroides

Native tubular membranes were purified from the purple non-sulfur bacterium Rhodobacter sphaeroides. These tubular structures contain all the membrane components of the photosynthetic apparatus, in the relative ratio of one cytochrome bc1 complex to two reaction centers, and approximately 24 bacteriochlorophyll molecules per reaction center. Electron micrographs of negative-stained membranes diffract up to 25 A and allow the calculation of a projection map at 20 A. The unit cell (a = 198 A, b = 120 A and gamma = 103 degrees) contains an elongated S-shaped supercomplex presenting a pseudo-2-fold symmetry. Comparison with density maps of isolated reaction center and light-harvesting complexes allowed interpretation of the projection map. Each supercomplex is composed of light-harvesting 1 complexes that take the form of two C-shaped structures of approximately 112 A in external diameter, facing each other on the open side and enclosing the two reaction centers. The remaining positive density is tentatively attributed to one cytochrome bc1 complex. These features shed new light on the association of the reaction center and the light-harvesting complexes. In particular, the organization of the light-harvesting complexes in C-shaped structures ensures an efficient exchange of ubihydroquinone/ubiquinone between the reaction center and the cytochrome bc1 complex.     

Characterization of the reaction center bound tetraheme cytochrome of Rhodocyclus tenuis

Properties of the tetrahemic reaction center bound cytochrome have been investigated by different techniques. The mid-point potentials of the four hemes were determined by redox titration. The best fit of the data was obtained with a (n = 1) Nernst curve by using the following values of the redox parameters: Em = +420 mV for the two high-potential hemes and Em = +110 and +60 mV for the two low-potential hemes. The mid-point potentials of the two high-potential hemes are the highest reported so far. The spectral properties of the four hemes in the alpha-band have been determined by absorption spectroscopy and measurements of light-induced difference spectra in membranes of Rhodocyclus tenuis. The two high potential hemes present very similar spectra centered at 557 nm. The absorption spectra of the two low-potential hemes are very similar, and their alpha-band centered around 551 nm. Spectral properties at 100 K and the linear dichroism of optical transitions allow the determination of the relative orientations of the hemes with respect to the membrane plane. The orientation patterns thus obtained corresponds to none of the arrangements described so far for reaction center bound cytochromes.     

Battery energy storage-based system damping controller for alleviating sub-synchronous oscillations in a DFIG-based wind power plant

This paper presents the issue of the Sub-synchronous resonance (SSR) phenomenon in a series compensated DFIGbased wind power plant and its alleviation using a Battery Energy Storage-based Damping Controller (BESSDCL). A supplementary damping signal is developed considering the angular speed deviation and is incorporated into the BESS control system. Wide-area Measurement System data is used to determine the angular speed deviation. A linearized system model is developed to perform eigenvalue analysis, and to detect and examine unstable SSR modes. The variation of wind speed and three-phase fault are also taken into consideration to validate the robustness of the controller. To further verify the efcacy of the proposed damping controller, time-domain simulations are performed using MATLAB/Simulink. The application of the proposed BESSDCL stabilizes all the unstable system modes efectively at wind speeds of 7 m/s, 9 m/s, and 11 m/s, and at 40%, 50%, and 60% series compensation levels, as well three-phase fault conditions.