Sur la stéréospécificité de la ribonucléoside-diphosphate-réductase: préparation de désoxyribonucléosides pyrimidiques deutérés

Methyl 2-deoxy-3,5,6-tri-O-p-nitrobenzoyl- -ribo-hexofuranoside was converted into the glycosyl halide which was then condensed with 2,4-bis(trimethylsilyloxy)-pyrimidine in the presence of mercuric chloride to give, after alkaline methanolysis, 1-(2-deoxy-β- -ribo-hexofuranosyl)uracil, in a yield too low for the reaction to be applied to deuterated compounds. Methyl 2-deoxy- -allofuranoside-2-d was degraded into methyl 2-deoxy- -arabinofuranoside-2-d. Its di-p-nitrobenzoate was converted into the glycosyl halide which was coupled with 2,4-bis(trimethylsilyloxy)-pyrimidine to give, after alkaline hydrolysis, deuterated deoxyuridine. Thiationammonolysis of a mixture of the 3′,5′-di-p-nitrobenzoates of the latter compound and its anomer gave the corresponding deoxycytidines. Comparison of the n.m.r. spectra of these compounds to that of deuterated deoxycytidine, prepared by the enzymic reduction of cytidine 5′-pyrophosphate with the Escherichia coli system in the presence of deuterium oxide confirmed that the substitution of a hydroxyl group by a hydrogen atom proceeds with retention of configuration.     

Interactions de la chloroquine avec la ferriprotoporphyrine IX: Étude par résonance magnétique nucléaire

Chloroquine is still the antimalarial drug which is the most utilized. Nevertheless the molecular mode of action of this drug is not very well understood. When mouse erythrocytes injected with Plasmodium berghei are exposed to chloroquine, the first biochemical event is rapid accumulation of the drug. This process is energy dependent, saturable and competively inhibited by drugs of the same therapeutic class (Quinine, Amodiaquine, Mefloquine). Receptors for chloroquine have been proposed for the process of accumulation. The nature of the chloroquine receptor is presently the subject of debates. The latest hypothesis proposed by Chou and coll. [12], is that ferriprotoporphyrin IX, formed by the degradation of hemoglobin by the parasite, binds to chloroquine with a dissociation constant of 3.5.10⁻⁹ M. We studied here the molecular interactions between these two species by Proton Nuclear Magnetic Resonance in order to elucidate the nature and the geometry of were undertaken.The perturbations of the NMR spectra of chloroquine (10⁻² M) induced by addition of hematin or hemin were measured. Two types of measures were indertaken.The first study carried out in organic solvent (DMSO) has shown that the interaction occured between the acidic functions of hemin and the sidechain nitrogen of chloroquine. The iron atom was not implicated in this process.The second study carried out in aqueous medium (phosphate buffer; 0.1 M; pH = 7) allowed us to demonstrate that chloroquine is able to intercalate into a polymer of hematin. The quinoleic nucleus of chloroquine was intercalated between two dimers of hematin as shown by the broadening of the signal of the quinoleic protons due to very large increase in the correlation time.Finally it was shown that chloroquine is associated as a dimer in aqueous medium by hydrophobic interactions. The association constant is 5.5 M⁻¹.     

Contribution à l'étude de la structure de la chromatine: I - Etude physico-chimique de la stabilité de la chromatine

Physicochemical studies of calf thymus chromatin were performed on micromicellar suspensions by thermal denaturation. These diluted suspensions were obtained, by a controlled shearing method, from a compact gel chromatin. Sedimentation and free-flow electrophoresis determined the size distribution of these particles. The most important result is a new transition on the melting profiles corresponding to a sudden increase of solution turbidity. This chromatin solution transition occurs at a higher temperature than usual DNA transition. The degree of « turbidity transitiondiminishes with micelle size but disappears when they are very mildly degraded by DNAases and when F₁ histone fraction is removed.This transition is not only size dependent but also depends on the micellar structure. This phenomenon is interpreted as an excluded volume effect by contact between compact and native regions of nucleoprotein micelles and denatured coils of DNA. Our study tried to show that the degree of turbidity transition can be a criterion of chromatin native structure.     

La diversité floristique de la végétation psammophile de la région de Tlemcen (nord–ouest Algérie)

This study is devoted to the analysis of the psammophyte of the coastal and semi-continental dunes in Tlemcen. Interesting results have been obtained, in particular, on the biological and ecological aspects of the psammophyte. The interpretation from Factoriel analysis of correspondences enabled us to identify the different phytosociological classes (Cakiletea maritimae, Ammophiletea, Quercetea ilicis, Therobrachypodietea and Stellarietea mediae). Some of these classes (Cakiletea maritimae and Ammophiletea) inhabit, exceedingly well, the embryonic dunes. Some species (Therobrachypodietea) colonize the quickset dunes. Lastly, some others (Quercetea ilicis) settle in the more mature and stable dunes. By using the phytosociological and phytodynamical data, we have been able to understand the vegetation and its diversity. To cite this article: H. Stambouli-Meziane et al., C. R. Biologies 332 (2009).     

Activité oxydasique de l''oxydoréductase de la xanthine, spécifique de la classe des mammifères

In every species other than mammals xanthine oxidoreductase behaves as a dehydrogenase, never as an oxidase. In three mammalian species, the enzyme acts intracellularly as a dehydrogenase, but its class-specific ambivalence allows its extracellular conversion into an oxidase.

Résumé

En dehors de la classe des Mammifères, l'oxydoréductase de la xanthine ne se comporte jamais comme une oxydase. Chez les Mammifères, une ambivalence de la molécule permet l'expression d'une activité déshydrogénasique (NAD) dans la cellule, et d'une activité oxydasique en dehors de la cellule.