Primary structure and electrophysiological characterization of two almost identical isoforms of toxin from Isometrus vittatus (family: Buthidae) scorpion venom.

Two almost identical proteins with 70 amino acid residues each, closely packed by four disufide bridges, and molecular masses of 7899.5 and 7884.7 were isolated and sequenced from the venom of the scorpion Isometrus vittatus from Pakistan. They differ by an acidic amino acid residue (glutamic or aspartic) at the same position 55 of the peptide chain, however, they exhibit the same length, the same charge and are undistinguishable when separated by C(18) reverse phase HPLC. The mixture of the two proteins called IsomTx1 depolarizes the cockroach isolated axon; artificial repolarization is followed by sustained repetitive activity, artificial hyperpolarization facilitates bursting activity observed as an answer to rapid depolarization to -60 mV. The depolarization is antagonized by TTX. In voltage-clamp experiments IsomTx1 increases axonal sodium permeability which has a particular importance between resting and threshold potentials and moderately slows down the fast inactivation. These characteristics closely resemble those of other anti-insect scorpion toxins classified as contractive toxins from Androctonus and Buthotus venoms

Présence de conodontes dans les calcaires de Rosan (Ordovicien moyen à supérieur, massif armoricain)

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Réflexion d'une onde électromagnétique sur le front d'onde de détonation dans les mélanges gazeux

The velocity of propagation of stable detonation waves in propane-oxygennitrogen mixtures was measured and the evolution observed during the phases of formation or destruction by means of a simple experimental device using the Doppler effect in the centimetric wave-length band. The oscillographic records of this effect have enabled us to characterize by a particular frequency the instability phenomena which are in connexion with the structure of the observed detonation waves.La célérité de propagation des détonations stables des mélanges propane-oxygène-azote a été mesurée et son évolution suivie pendant les phases de formation ou de destruction, au moyen d'un dispositif simple utilisant l'effet Doppler en ondes centimétriques. Les enregistrements oscillographiques obtenus de cet effet permettent de caractériser par une fréquence particulière des phénomènes d'instabilité liés à la structure des détonations observées