Etude de quelques propriétés de la phosphofructokinase érythrocytaire de l'homme normal

Human erythrocyte phosphofructokinase was purified 150 fold by DEAE cellulose adsorption and ammonium sulfate precipitation.At pH 7,5 the enzyme exhibits allosteric kinetics with respect to ATP, fructose 6 phosphate, and Mg²⁺.ATP at high concentration acted as an inhibitor and ADP, 5′AMP, 3′,5′, AMP, acted as activators. Both effectors seemed to decrease the homotropic interactions beetween the fructose 6 phosphate molecules.The activators increased the affinity of phosphofructokinase for the substrate (F6P), the inhibitor decreased it.These ligands had no effect on the maximum velocity of the reaction except in the case of ADP.Interactions between the substrates and the effector ligands on the enzyme were considered in terms of the Monod - Changeux - Wyman model for allosteric proteins.With GTP and ITP, no inhibition was observed. At saturing concentration of GTP, ATP still inhibited phosphofructokinase.Both 3′5′ AMP and fructose 6 phosphate increased the concentration of ATP required to produce an inhibition of 50 %.Citrate, like ATP, inhibited phosphofructokinase by binding most likely at the same allosteric site. Erythrocyte phosphofructokinase is inhibited by 2–3 DPG.The study of the relation log V max = f (pH) suggested, that the active center contains at least one imidazole and one sulfhydryl group.     

Etude experimentale de L′auto-association des molécules modèles dipeptidiques. III. Influence de la dimerisation stéréosélective sur les spectres de résonance magnétique protonique

Proton magnetic resonance spectra of model dipeptide molecules R₁–C′₁O₁–N₂H₂–CHR₂–C′₂O₂–N₃H₃–R₃ in CCl₄ solutions exhibit splited signals when investigating on mixtures of L and D enantiomers differing from the racemic composition. The major effect is observed on amide proton signals which are the ones most sensitive to the ratio of aggregation. The stereoselective dimerization of enantiomeric molecules in the so-called C₅ conformational state is shown to be responsible for such a phenomenon, the intensity of which depends on the bulkiness of the side chain R₂. A theoretical approach is proposed which gives predictions in close agreement with our own experimental findings.     

Accumulations osseuses en périphérie de terriers de petits carnivores : les stigmates de prédation et de fréquentation

Faunal remains from spoil heaps of two burrows inhabited by small carnivores (fox and badger) are analysed from a taphonomical point of view. This analysis provides characteristics for bone accumulation produced by small carnivores and will be a powerful tool for deciphering site formation about the occupational alternation of small carnivores and humans. Identified species were grouped by size classes. Faunal spectrum is composed by varied species of microfauna (70%), mesofauna (30%). Macromammal remains are under represented (less than 1%) and come from scavenged carcasses. Predators and consumed species are compared on the basis of the skeletal part representation, age classes and recording of predation marks (gnawed and digested bones). Skeletal part representation shows that all taxons exhibit a low-representation of axial skeleton and autopodial bones. Predators show a high representation of hind limb bones and a low representation of the fore limb bones whereas consumed species exhibit a reverse pattern. Mortality curve analysis provides an attritional profile for carnivores and helps for the establishment of the season of occupation of the burrow. Adults largely dominate consumed species. Moreover, predation marks are found in 1% of the carnivores’ bones and from 15% to more than 40% on prey bones. The large-sized prey bones only wear gnawed marks (20%) and anthropic marks (10–20%) whereas microfaunal remains exhibits more digested marks (40%) than gnawing stigmata (5%). Medium-sized animals bones wear both marks and with the same proportions (10–15%).     

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).     

Application paléoécologique de la méthode d''analyse factorielle en composantes principales: Interprétation des microfaunes de foraminifères planctoniques quaternaires en Méditerranée. III. Les séquences paléoclimatiques. Conclusions générales

The statistical analysis (Q mode) of the microfauna of 135 bottom and core samples from the Mediterranean provides evidence of the predominating local conditions in each of the two basins.

Temperature, which plays a primary role in the distribution of foraminiferal species, only takes second place when one considers the regrouping of the layers.

Once the temperature factor is identified, its variations provide a precise climatic curve with the advantage of not having to make any subjective interpretation of the assemblages.

Résumé

L'analyse en mode Q des microfaunes de 135 échantillons de Méditerrannée (niveaux de surface et carottages) met en évidence la prédominance des conditions locales propres à chacun des deux bassins.

La température, qui joue un rôle primordial dans la répartition des espèces de Foraminifères, n'intervient qu'en second lieu lorsqu'on considère les regroupements des niveaux.

Une fois le facteur thermique identifié, ses variations fournissent une courbe climatique précise qui présente l'avantage de ne nécessiter aucune interprétation subjective des assemblages.     

Analyse formelle de circuits de régulation génétique: le contrôle de l'immunité chez les bactériophages lambdoïdes

This paper is an attempt to describe and analyze in formal terms a genetic circuit which is rather complex and reasonably well disentangled: the control of immunity in lambdoid bacteriophages. Known models are expressed as logic equations, which relate the stade of activity of genes to variables of three kinds: genetic variables which describe the genotype of the organism, environmental variables like temperature and memorization variables. The value of each memorization variable (presence or absence of a gene product) is related to the value of the corresponding function (operation or not of the gene) by two characteristic time delays, an «establishment delay and a «decay delay.From the equations, one can derive matrices which facilitate comparison between models by showing which stable states are predicted by each model. Implications of current models, which had apparently remained cryptic, have been realized and experimentally tested.From the matrices, one can derive graphs which show the pathways (sequences of states) consistent with each model. These graphs are frequently branched and in these cases one has to analyze which conditions determine that one pathway rather than another one, is followed.     

Mesure des déclins de l'intensité et de l'anisotropie de fluorescence du pérylène en présence de membranes d'érythrocyte de pigeon: Comparaison avec un milieu isotrope visqueux

Using synchrotron radiation as the excitation light, we studied the fluorescence parameters of perylene incubated with pigeon erythrocyte membranes and with an isotropic viscous medium, the Primol 342 oil.From 4 to 37°C, we observed a single lifetime of 4.5 ns in the oil and two with the membrane (τ₁ = 1−1.4 ns and τ₂ = 5.4−6.1 ns). The dependence upon temperature of the rotation correlation time of perylene () in the oil was characteristic of an isotropic medium, whereas the limiting value of anitropy (r ∞) was zero. With the membrane, γ ∞ decreased from 0.14 to 0.06 and from 2.9 to 0.5 ns, indicating a greater amplitude and frequency of molecular motions.The addition of chlorpromazine, indomethacine, tetracaine, n-octylamine, octanol or octanoic acid to the membrane decreased the τ₁ and τ₂ values. This would stem from the desorganization of the membrane induced by the drugs.     

Transport axonal de protéines marquées dans le motoneurone géant de l'écrevisse

Isolated abdomens of crayfish were maintained in vitro and lysine (-³H) was intracellularly injected into one of the giant motoneuron of the ventral cord ganglia by iontophoresis. Membrane potentials ranging between -60 and -70 mV were recorded all along the experiment. Light microscope radioautographs showed an intense reaction over the injected nerve cell body and the initial segment of its axon; most of the surrounding tissues were free of radioactivity when the diffusion of the injected lysine (-³H) was prevented by adding cold lysine to the bathing medium. Some exchange of label was however noted with electrically coupled axons and glial sheaths. No radioactive protein could be traced in the numerous nerve endings of the neuromuscular junction. Nonetheless when a ligature was placed on the nerve root, the amount of accumulated radioactivity was increased from 3 to 6 h. in the axon of the injected motoneuron only. Electron microscope radioautographs indicate that the fast transported proteins were mainly associated with the endoplasmic reticulum and the axonal membrane. It is concluded that the visualization of the nerve endings was limited by the dispersion of the label into the numerous thin terminal branchs of the axon; however the combination of iontophoretic injection and radioautography permits to trace endogenous protein along the axon and to study molecular exchanges with other cells.     

Activité DNA-polymérase nucléaire dans les spermatozoides de souris et évolution de cette activité au cours de la spermatogenèse

The presence of a nuclear DNA polymerase activity has been demonstrated in the mouse testis by a cytochemical method. The enzyme was present in the nuclei of the various cell types of mouse spermatogenesis, including spermatozoa. The nuclear activity increased during meiotic prophase and then decreased in spermatids and spermatozoa. A peculiar attention was devoted to the properties of the nuclear DNA polymerase present in spermatozoa. All four deoxyribonucleoside-triphosphates were needed for optimal activity; the acid-insoluble radioactive product obtained by polymerization in situ was completely removed by DNase, but not by RNase nor by pronase. The reaction of polymerization was DNA-dependent, sensitive to high concentrations of KCl and not affected by NEM nor by PHMB.     

Préparation et forme sérique de la protéine réactive C de lapin

The preparation of rabbit C-reactive protein (CRP) involves a single step affinity chromatography. This preparation takes advantage of the calcium-dependent affinity of CRP for an agarose gel bearing 2-aminoethanol dihydrogen-phosphate as a ligand. A prior chromatography on agarose gel without the ligand allows the uptake of the serum amyloid P-component (SAP).The CRP prepared according to this method is able to form precipitating complexes in agarose with rabbit lipoproteins. The specificity of these interactions is studied. It is demonstrated that CRP-High Density Lipoproteins (HDL) association produces a second precipitation arc when the pure CRP is revealed by a specific antiserum in agarose. Moreover, CRP in the serum is shown to be in the bound form only, and the binding involves Low Density Lipoproteins (LDL) exclusively.     

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.     

Etude ultrastructurale comparée du processus de dégradation de l'hémoglobine par P. berghei (Vincke et Lips, 1948) en fonction de l'état de maturité de la cellule hǒte1

By serial sectioning and 3D reconstruction we have been able to demonstrate that the type of system for hemoglobin digestion in two strains of Plasmodium berghei, N and RC, is dependent on the maturity of the host cell. In parasites growing in erythrocytes, both systems for the endocytosis of hemoglobin—micropinocytosis and the cytostomal system (i.e. a cytostome budding a cytostomal tube that releases food vacuoles)—are fully functional and produce a great quantity of residual pigment. Parasites growing in reticulocytes have a disrupted cytostomal system; no tube is formed and only food vacuoles are visible in their cytoplasm. Residual pigment is smaller in size and in quantity. The reduced quantity of pigment in reticulocytes is explained by our observation of the exocytosis of pigment. We propose a hypothesis that relates the process of degradation of hemoglobin to the maturity of the host cell and a possible mechanism of protection against chloroquine, a drug known for its affinity for malarial pigment.     

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.     

Caractérisation de la membrane liée au chromosome replié isolé de Escherichia coli

Phospholipid analysis of the membranes associated with fast sedimenting folded chromosomes prepared by lysis of E. coli CR 34 shows that both inner and outer membranes are parts of the complex, in proportions not very different from that found in the whole bacteria.During the preparation of the folded chromosomes, the most recently synthesized molecules of phosphatidylglycerol and phosphatidylethanoamine are more sensitive to solubilisation, particularly those from the cytoplasmic membrane. Identification of a dominant fraction, the outer membrane, in some complexes, results from a preferential solubilization of the inner membrane.These results do not favor any specific association between the folded chromosome and the membranes.