Biochemical characterization and nuclear magnetic resonance structure of novel alpha-conotoxins isolated from the venom of Conus consors.

Two novel alpha-conotoxins were purified and characterized from the venom of the fish-hunting cone snail Conus consors. These peptides were identified by screening HPLC fractions of the crude venom and by binding experiments with Torpedo nicotinic acetylcholine receptor. The toxins named alpha-CnIA and alpha-CnIB exhibited sequences of 14 and 12 amino acids, respectively. The alpha-CnIA represents the main alpha-conotoxin contained in the venom, whereas alpha-CnIB is present in a relatively small amount. Chemical synthesis of alpha-CnIA was carried out using the Fmoc methodology by selective disulfide bond formation. The biological activity of the toxin was assessed in fish and mice. The alpha-CnIA inhibited the fixation of iodinated alpha-bungarotoxin to Torpedo nicotinic acetylcholine receptors with an IC50 of 0.19 microM which can be compared to the IC50 of 0.31 microM found for the previously characterized alpha-MI isolated from the piscivorous Conus magus. The synthetic alpha-CnIA blocked spontaneous and evoked synaptic potentials in frog and mouse isolated neuromuscular preparations at sub-micromolar concentrations. Solution NMR of this toxin indicated a conformational heterogeneity with the existence of different conformers in solution, at slow and intermediate exchange rates relative to the NMR chemical shift time scale, similar to that reported for alpha-GI and alpha-MI. NMR structures were calculated for the major NMR signals representing more than 80% of the population at 5 degrees C.

[Use of thiopental in man. Determination of this drug and its metabolites in plasma and urine by liquid phase chromatography and mass spectrometry]. / Utilisation du thiopental chez l'homme. Détermination de ce médicament et de ses métabolites dans le plasma et les urines par chromatographie en phase liquide et spectrométrie de masse.

Thiopental is an anaesthetic drug which is currently used for cerebral resuscitation. In this last indication the drug is administrated at high doses over a period of several days. Under clinical trials thiopental and two metabolites namely 5 ethyl-5 (1' methyl-3' hydroxy-butyl) 2 thiobarbituric acid and 5 ethyl-5 (1' methyl-3' carboxy-propyl) 2 thiobarbituric acid have been determined by high performance liquid chromatography and mass spectrometry. In human plasma high concentrations of thiopental and 5 ethyl-5 (1' methyl-3' hydroxy-butyl) 2 thiobarbituric acid and a lower concentration of 5 ethyl-5 (1' methyl-3' carboxy-propyl) 2 thiobarbituric acid have been found. In urine samples these metabolites are excreted in large and approximately equal quantities, whereas small amounts of thiopental were recovered.