E. Fernández-Sánchez

Mechanism suppressing glycogen synthesis in neurons and its demise in progressive myoclonus epilepsy

Glycogen synthesis is normally absent in neurons. However, inclusion bodies resembling abnormal glycogen accumulate in several neurological diseases, particularly in progressive myoclonus epilepsy or Lafora disease. We show here that mouse neurons have the enzymatic machinery for synthesizing glycogen, but that it is suppressed by retention of muscle glycogen synthase (MGS) in the phosphorylated, inactive state. This suppression was further ensured by a complex of laforin and malin, which are the two proteins whose mutations cause Lafora disease. The laforin-malin complex caused proteasome-dependent degradation both of the adaptor protein targeting to glycogen, PTG, which brings protein phosphatase 1 to MGS for activation, and of MGS itself. Enforced expression of PTG led to glycogen deposition in neurons and caused apoptosis. Therefore, the malin-laforin complex ensures a blockade of neuronal glycogen synthesis even under intense glycogenic conditions. Here we explain the formation of polyglucosan inclusions in Lafora disease by demonstrating a crucial role for laforin and malin in glycogen synthesis.

Solubility parameters of gas chromatographic mixed stationary phases

Gas chromatography was used to measure activity coefficients, ϒ∞, partial molar free energies of mixing, ΔG−∞1, Flory-Huggins interaction parameters, χ∞, and its enthalpic and entropic contributions, of a number of solutes on five single and fourteen mixed stationary phases at 120°C. Solubility parameters of the stationary phases, δ2, were deduced by the method of DiPaola-Baranyi and Guillet for the different solute-stationary phase combinations. The polymer-polymer interaction parameter, χ′2,3, was also calculated for the various mixed systems.

Contribution to the study of micropacked columns in gas chromatography

Abstract Several chromatographic columns made from glass tubes of I.D. 0.5–1 mm and with solid support particle sizes of 100–120 and 120–140 mesh were evaluated. The effect of liquid film thickness, column diameter, permeability and particle diameter to column diameter ratio on column efficiency is discussed. The pressure drop at the optimum gas velocity per unit column length and per theoretical plate is considered. A column is discussed with 6250 theoretical plates per metre, and others, les efficient per unit length, with a total of about 60 000 theoretical plates which can be run at about 7 kg/cm 2 if nitrogen is used.

Evaluation of the effect of the cyanopropyl radical on the interaction of the methylene group with silicone stationary phases

Values of the solute-polymer interaction parameter of n-alkanes and polar substances between 90C and 200°C were obtained on two packed columns (OV-101 and OV-105). Experiments carried out with a capillary column confirmed that with non-polar solute-polymer systems the values of both the specific retention volumes and the thermodynamic parameters derived from them are equivalent to those obtained with packed columns. The results showed that n-alkanes mix better with OV-101 and polar substances are better solvents of OV- 105. The differences are small, however. Partial molar enthalpies and free energies of solution and mixing were calculated. The contribution of the methylene group of the n-alkanes to the thermodynamic parameters of solution was evaluated. The effect of cyanopropyl group substitution on the contribution of the methylene group to the partial molar free energy of solution of n-alkanes was found to be roughly linear with the cyanoalkyl group content, decreasing as the polarity of the polymer increases. The solubility parameter of the stationary phase increases only slightly when a 5% substitution of cyanopropyl groups is introduced in the polymer.

Programmed-temperature retention indices : A survey of calculation methods

Abstract Retention temperatures of various solutes were measured on an OV-105 column under different heating rates. The experimental results agree with those evaluated by means of the equation of Curvers et al. Several methods of assigning programmed temperature retention indices to each solute were tested. Comparison of the results does not allow a clear choice of any of the methods, although a procedure based on an interpolation through the use of cubic splines polynomials is preferred. The sensitivity of the various procedures towards small changes in the input data is reported.

Gas chromatographic comparative study of superox 20m immobilized in different ways

Abstract Three capillary columns of Superox 20M, two of them immobilized in different ways, were prepared. All columns showed a transition zone from adsorption of the solutes at low temperatures to absorption at higher temperatures. The minimum allowed operating temperature of the column was found to change from 64°C to 50°C when the polymer was immobilized. Partial molar enthalpies of mixing showed that alkanes are poor solvents of the stationary phase, while aromatics are good solvents, with little dependence on the degree of immobilization. It might be expected that Superox 20M will mix well with polymers with phenyl components, and will not mix with polymers of long hydrocarbon-type chains.

Mixed stationary phases in gas—liquid chromatography : Partition coefficients and retention indices in OV-101-OV-25, OV-101-carbowax 20M and OV-225-SP-2340 mixtures

Abstract Partition coefficients of n-alkanes and other substances were measured at 393 K on mixed stationary phase columns prepared by mixing OV-101 with OV-25, OV-101 with Carbowax 20M and OV-225 with SP-2340. The results are examined with respect to the Purnell—Vargas de Andrade and Perry—Tiley relationships. The solvent—solvent interaction parameter was calculated in the three systems. When the value of this parameter is higher than 2 a clear departure from the linear approximation was observed. Retention indices were also calculated and compared with those predicted by the above relationships.

Thermodynamic characterization of Superox 20M by inverse gas chromatography

Abstract Inverse gas chromatographic experiments carried out between 80 and 140°C were used to characterize Superox 20M deposited on glass capillary columns, using 28 substances belonging to five different chemical types. No absorption in the gas—liquid interphase was observed except in three cases corresponding to the highest molecular masses. The thermodynamic parameters of solution and mixing and the Flory—Huggins solute—stationary phase interaction parameter were measured. The dependences of all magnitudes on temperature and chain length were also calculated, and conclusions on the relationship between their values and the chromatographic behaviour of the solutes in the stationary phase were drawn. The solubility parameter of Superox 20M was measured between 80 and 140°C and was found to have a linear dependence on temperature. Values at 50, 64 and 280°C were deduced.

Spontaneous O2 release from SmBa2Cu3O7−x high Tc superconductor in contact with water

Abstract The high T c superconductors of compostion RBa 2 Cu 3 O 7−x (R = Y, La, lanthanide) are known to strongly react with water, which leads to compound decomposition and loss of their superconducting properties. A peculiar feature of this reaction is oxygen evolution. From a mass spectrometric analysis of the evolved oxygen we have been able to show that O 2 is released from the superconductor lattice. This unusual behaviour, which is specific of some metal peroxides, must be related to the peculiar electronic structure of these materials, and more concretely to the existence of O − and/or O 2 2− ions stabilized in the superconductor lattice. Our finding is consistent with the occurrence of holes delocalized in energy levels of O: 2p parentage, as recently found from angle resolved photoemission experiments with YBa 2 Cu 3 O 7 samples.

Reduction of the number of characterizing probes in gas chromatography by factor analysis

Determination du comportement chromatographique des phases stationnaires, a partir de 10 solutes types