CIRCULAR DICHROISM OF LIGHT-HARVESTING COMPLEXES FROM PURPLE PHOTOSYNTHETIC BACTERIA

The CD spectra of a range of antenna complexes from several different species of purple photosynthetic bacteria were recorded in the wavelength range of 190 to 930 nm. Analysis of the far UV CD (190 to 250 nm) showed that in each case except for the B800-850 from Chr. vinosum the secondary structure of the light-harvesting complexes contains a large amount of α-helix (50%) and very little 0-pleated sheet. This confirms the predictions of the group of Zuber of a high a-helical content based upon consideration of the primary structures of several antenna apoproteins. The CD spectra from the carotenoids and the bacteriochlorophylls show considerable variations depending upon the type of antenna complex. The different amplitude ratios in the CD spectrum for the bacteriochlorophyll Qy, Qx and Soret bands indicate not only different degrees of exciton coupling, but also a strong and variable hyperchromism (Scherz and Parson, 1984a, b)

Tumor suppressor fumarate hydratase is phosphorylated and regulated by AMP-activated protein kinase

International audienc

Coagulation at the blood-electrode interface: the role of electrochemical desorption and degradation of fibrinogen

The influence of electrochemistry on the coagulation of blood on metal surfaces was demonstrated several decades ago. In particular, the application of cathodic currents resulted in reduced surface thrombogenicity, but no molecular mechanism has been so far proposed to explain this observation. In this article we used for the first time the quartz crystal microbalance with dissipation monitoring technique coupled with an electrochemical setup (EQCM-D) to study thrombosis at the blood-electrode interface. We confirmed the reduced thrombus deposition at the cathode, and we subsequently studied the effect of cathodic currents on adsorbed fibrinogen (Fg). Using EQCM and mass spectrometry, we found that upon applying currents Fg desorbed from the electrode and was electrochemically degraded. In particular, we show that the flexible N-terminus of the α-chain, containing an important polymerization site, was cleaved from the protein, thus affecting its clottability. Our work proposes a molecular mechanism that at least partially explains how cathodic currents reduce thrombosis at the blood-electrode interface and is a relevant contribution to the rational development of medical devices with reduced thrombus formation on their surface

Phase Behavior of Aqueous Na-K-Mg-Ca-CI-NO3 Mixtures: Isopiestic Measurements and Thermodynamic Modeling

A comprehensive model has been established for calculating thermodynamic properties of multicomponent aqueous systems containing the Na{sup +}, K{sup +}, Mg{sup 2+}, Ca{sup 2+}, Cl{sup -}, and NO{sub 3}{sup -} ions. The thermodynamic framework is based on a previously developed model for mixed-solvent electrolyte solutions. The framework has been designed to reproduce the properties of salt solutions at temperatures ranging from the freezing point to 300 C and concentrations ranging from infinite dilution to the fused salt limit. The model has been parameterized using a combination of an extensive literature database and new isopiestic measurements for thirteen salt mixtures at 140 C. The measurements have been performed using Oak Ridge National Laboratory's (ORNL) previously designed gravimetric isopiestic apparatus, which makes it possible to detect solid phase precipitation. Water activities are reported for mixtures with a fixed ratio of salts as a function of the total apparent salt mole fraction. The isopiestic measurements reported here simultaneously reflect two fundamental properties of the system, i.e., the activity of water as a function of solution concentration and the occurrence of solid-liquid transitions. The thermodynamic model accurately reproduces the new isopiestic data as well as literature data for binary, ternary and higher-order subsystems. Because of its high accuracy in calculating vapor-liquid and solid-liquid equilibria, the model is suitable for studying deliquescence behavior of multicomponent salt systems