Méthylations biologiques chez le crabe Carcinus maenas; inhibition in vitro par une fraction purifiée extraite des glandes androgènes

Extracts from muscles, testis, seminal vesicles and ovaries of the Crab, Carcinus maenas, have been studied in vitro, in presence of [¹⁴C]-methyl S-adenosylmethionine, with an E. coli tRNA as methyl acceptor. The highest level of methylases is found in the testis. It has been reported previously that a purified fraction extracted from the androgenic glands of Carcinus maenas inhibits the vitellogenesis in ovaries. We now show that the same fraction inhibits tRNA methylation in an extract of testis as methylase; a 50 per cent inhibition is obtained with about 10 μg of a purified fraction corresponding to 15 glands. With an enzymatic preparation from the ovaries, a 50 per cent inhibition of the tRNA methylase is observed with the purified extract from 4 glands.     

Inhibition par les lipoprotéines de haute densité HDL2 et HDL3 de la synthèse du DNA et des stérols des lymphocytes humains stimulés par la concanavaline A.

Lipoproteins HDL₂ and HDL₃ inhibit DNA synthesis and sterol synthesis in human Con A-stimulated lymphocytes cultured in a medium supplemented with 20 per cent lipoprotein deficient serum. On the basis of the amount of proteins added, HDL₂ is more efficient on DNA and sterol synthesis than HDL₃ and less efficient than LDL. However, on the basis of the amount of cholesterol added, the inhibition of sterol synthesis induced by these three lipoproteins is not significantly different. At all concentrations of these three lipoproteins, the inhibition of sterol synthesis is higher than the inhibition of DNA synthesis.     

Étude de la fixation de faible affinité du Ca par les membranes externe et interne des mitochondriest et par le réticulum endoplasmique lisse et rugueux de foie de rat

Two classes of low-affinity Ca²⁺-binding sites have been shown to exist. One type dissociates as pH rises, thereby increasing the amount of bound Ca²⁺. The other type, which does not change in number, has an affinity for Ca²⁺ which is dependent on ionic strength. The former is possibly a phospholipid, the latter possibly a protein.Under our experimental conditions, the inner mitochondrial membrane contained binding sites of the second class ony while other membranes contain both types. Rough endoplasmic reticulum contains yet another class of sites at the ribosomal level.

Résumé

L'existence de deux catégories de sites de fixation de faible affinité du Ca²⁺ a été mise en évidence. Les uns se dissocient de plus en plus quant le pH s'éléve permettant une augmentation des quantités de Ca²⁺ fixé, les autres sont invariables en nombre, mais leur affinité pour le Ca²⁺ est dépendante de la force ionique du milieu. Les premiers pourraient étre de nature phospholipidique, les seconds de nature protéique.Dans nos conditions expérimentales, la membrane interne des mitochondries possède uniquement des sites de la seconde catégorie. Les autres membranes renferment simultanément les deux sortes de sites. Le réticulum endoplasmique rugueux possède des sites supplémentaires au niveau des ribosomes.     

Conformations et spectre Raman de l'acide ribonucléique de transfert, tRNA

The structure of yeast tRNA^Asp in aqueous solution has been studied in sight of Raman spectra recorded between 5 and 82°C. A conformational change is evidenced at 20°C and an endomelting is found around 70°C. This melting temperature, much higher than in tRNA-^Phe (near 50°C) is interpreted by the presence of a higher number of G-C bases in tRNA^Asp.At a same temperature, the Raman spectrum of a tRNA^Asp crystal is quasi-identical than that of an aqueous solution, indicating a high structural similarity except bands corresponding to G,C bases which show a more effective stacking of these bases in the solid.     

Modifications des propriétés cytophotométriques des ADN et des histones nucléaires au cours de la sénescence des tritons (Triturus vulgaris et Triturus cristatus)

DNA and histones were studied by cytophotometry, in cartilaginous cells from urodele amphibians (Triturus vulgaris and Triturus cristatus) during ageing. With the Feulgen reaction, the DNA colorability decreased and their acid hydrolysis was more difficult. The coloration of the histones linked to DNA in chromatin was also changed. The results are discussed in relation to numerous works on deoxyribonucleoprotein modifications during cell ageing.ADN et histones ont été étudiés par cytophotométrie dans les cellules cartilagineuses d'Amphibiens Urodèles (Triturus vulgaris et Triturus cristatus) au cours du viellissement. Nous avons observé une baisse des affinités tinctoriales des ADN et une augmentation de leur résistance á l'hydrolyse acide pratiquée dans le cadre de la réaction de Feulgen. La colorabilité des histones associées aux ADN dans la chromatine est aussi modifiée. Tous ces résultats sont discutés en liaison avec les nombreux travaux effectués sur les modifications des désoxyribonucléoprotéines au cours du viellissement cellulaire.     

Signification des caractères partagés entre Bennettitales et Cycadales. Implications de la découverte d''une Cycadale nouvelle du Cénomanien de l''Anjou (France)

The lagoonal Cenomanian formation (Lower Cretaceous) of clays of the region of Baugeois (north of Angers) has supplied an exceptionally well-preserved fossil flora: leaves, woody structures or/and reproductive organs of pteridophyta, gymnosperms and angiosperms. A well-preserved fossil plant found in a quarry “Le Brouillard” (8 km from Angers), has allowed a detailed morphological and structural study of this species. A comparative study with extant plants has confirmed an undoubted link between the contemporary genus Dioon (an endemic cycad from Mexico) and the fossil species. However, features observed on the lower epidermis of the leaflets, present a similarity with some Jurassic Bennettitales. This discovery, added to other common features shared by these two orders, raises questions about their relationships, thought to be different from a phylogenetic viewpoint.

Résumé

La formation lagunaire cénomanienne (Crétacé inférieur) des Argiles du Baugeois, au nord d'Angers, a fourni une flore fossile riche et exceptionnellement bien conservée: feuilles, structures ligneuses ou/et organes reproducteurs de ptéridophytes, de gymnospermes et d'angiospermes. L'excellent état de conservation d'un fragment de plante fossile, récolté dans la carrière Le Brouillard à 8 km d'Angers, a permis une étude détaillée de la morphologie et de la structure foliaire de cette plante. L'étude comparative avec des plantes actuelles a démontré l'existence d'un lien de parenté entre le genre Dioon (cycadale endémique du Mexique) et le fossile, mais des caractères originaux observés sur l'épiderme inférieur des folioles, présentent des similitudes avec certains genres de Bennettitales du Jurassique. Une telle découverte, ajoutée aux autres caractères communs préalablement décrits par d'autres auteurs, soulèvent à nouveau quelques questions sur les relations de parentés entre ces deux groupes supposés phylogénétiquement éloignés actuellement.     

Possibilitiés d'étude des variantes de la cholinestérase plasmatique humaine par électrophorèse d'affinitéPossibilities of study of the human plasma cholinesterase variants by affinity electrophoresis

Affinity electrophoresis has been applied to the study of the multiple molecular forms of three human plasma cholinesterase phenotypes (usual enzyme U, atypical enzyme A and intermediate UA). Electrophoreses were carried out in polyacrylamide gels containing a water-soluble macromolecular derivative of m-amino-(substituted)-phenyltrimethylammonium immobilized within the gel network.Apparent dissociation constants (K_{D app}) were estimated from the mobilities of the enzymes versus ligand concentration.The ratio of K_{D app} values of the molecular forms of phenotypes A and U which is approximately 2 is consistent with the hypothesis that the anionic site is altered in atypical enzyme.     

Cartographie de restriction comparée de la séquence d''ADN hautement répétée coupée par Bam HI chez Papio papio et P. cynocephalus

Highly repeated DNA sequences from two baboon species (Papio papio and P. cynocephalus) have been compared using restriction endonucleases. The two species share a 343 base pairs tandemly repeated DNA, that is cut once by Bam HI. Papio cynocephalus differs from P. papio by loss of an EcoRI star site in the repeated sequence.     

Présence des enzymes catalysant la biosynthèse d'UDP glucose dans une fraction légère de l'appareil de Golgi des hépatocytes de chat

A Golgi-rich fraction is prepared from cat hepatocytes by the means of a four-step sucrose density gradient. The material applied to this gradient is composed either of smooth microsomes prepared from healthy animals, or of total microsomes prepared from cat treated by 50 per cent ethanol (0.6 g/100 g body weight, administered by stomach tube).A light fraction (d : 1.10) is obtained by the two procedures. It does not show any glucose-6-phosphatase activity, but is enriched in sialyltransferase, known as a marker enzyme for Golgi apparatus. It also contains the three enzymes implicated in the biosynthetic pathway for UDP-glucose (glucokinase, phosphoglucomutase and UTP : glucose-1-phosphate uridylyltransferase).UDP-glucose being the ultimate substrate in membranous glucosylation reactions, these results could support the hypothesis that sugar-nucleotides necessary for the glycoprotein biosynthesis are produced in the Golgi vesicles directly.     

L'utilisation de services de santé et de médicaments par des personnes agées de Montréal qui re?oivent des soins maintien à domicile.

A survey was conducted among 160 persons aged 64 year or more in Montreal who were receiving home care. They answered at home a questionnaire on their use of health care services and drugs, and showed the interviewer all the drugs they were taking. In comparison with similar data from elsewhere, the use of health care services (an average of 8.0 encounters with a physician per person per year) and of drugs (an average of 5.3 per person) by this group seems high. Perhaps this group of people was obviously sicker than others of the same age, but this remains to be shown. Moreover, despite the reported frequency of health problems, it is uncertain whether such use of services and drugs was necessary. The question is raised whether the home care system is doing for the patient what it was intended to do.     

Distribution subcellulaire des protéine-kinases stimulables par l'AMP cyclique et des protéines réceptrices de l'AMP cyclique dans la thyroïde de porc

The distribution of cyclic AMP-dependent protein kinase activity in porcine thyroid glands has been studied. Enzyme activity catalyzing phosphorylation of exogenous substrate (protamine) from ATP, and cyclic AMP binding were determined in parallel in subcellular fractions purified by differential centrifugation and flotation on sucrose density layers. Both activities were found in all the studied fractions; they were quantitatively the highest in the cytosol but particles showed the highest specific activities.Latent protein-kinase activity was unmasked by action of detergents on microsomes (× 5–10 fold) and solubilized (85 to 99 p. cent of the initial total activity). Cyclic AMP binding capacity was also recovered in detergent-treated microsomal extracts in spite of reduced cyclic AMP binding in the presence of detergent.Protein kinase activity and cyclic AMP-binding proteins were less represented in purified nuclei than in microsomes. Again both activities were unmasked by detergent.Preparations highly enriched in Golgi membranes were compared to rough microsomal preparations. Higher protein kinase activity was detected in rough microsomes as compared to Golgi membranes, whereas the reverse was true for cyclic AMP binding. Both activities were equalized after detergent treatment. Since unmasking of protein kinase activity was the highest in Golgi membranes, this fraction contains more enzyme activity and cyclic AMP binding capacity than rough microsomes.The localization of endogeneous protein substrates of cyclic AMP-dependent protein kinases was investigated using purified soluble protein kinase subcellular fractions. The better endogeneous substrates seemed to be localized in the rough microsomal and in the nuclear fractions.     

Une nouvelle voie de biosynthèse de l'acide oléique dans les végétaux

Oleic acid biosynthesis in Cauliflower slices has been studied from the following radioactive precursors: ¹⁴C-acetate, ¹⁴C-decanoate, ¹⁴C-laurate, ¹⁴C-palmitate, ¹⁴C-stearate and ¹⁴C-hydroxyacids derived from ¹⁴C-decanoate. The higher incorporation yield was obtained withe ¹⁴C-decanoate or the hydroxyacids derived from it. A new biosynthetic pathway for oleic acid, implying the intervention of a β-γ-hydroxylaurate-dehydrase is discussed.     

Nouvelle découverte dans le Nord-Ouest de Madagascar et répartition géographique des espèces du genre Palaeopropithecus

During the field-work of 2003 in the Narinda peninsula in the Province of Mahajanga (North-West of Madagascar), we found a Palaeopropithecus of large size in the new cave “Raulin Zohy”. This fossil differs in morphology and size from the remains coming from other sites of this area and belonging to a new yet undescribed species. This discovery proves that two species of this genus existed in the costal area of the Province of Mahajanga. This Palaeopropithecus attributed to maximus species allows a reconsideration of the geographical distribution of this subfossil lemur species, and asks an interesting question about the biogeography on the small new species.     

Variations des zymogrammes estérasiques chez les larves de Palaemon serratus soumises à différentes durées de choc thermique

Palaemon serratus at larval stage 2, acclimatized at 16°, were subjected to a temperature increase of 15° for periods of 5, 20 or 40 min with or without return to the initial temperature for 12 h. The soluble protein concentration of larvae subjected to a thermal shock of 20 min duration is lower than in control larvae. Total esterase-2C activity per mg of soluble protein after a thermal shock of 20 min duration is less than in control larvae but, in contrast with larvae subjected to a shock of 40 min duration, the initial activity is restored after 12 hours. Esterase-2C activity zymograms, after polyacrylamide gradient gel electrophoresis, show twelve isozymes. The activity of each isozyme examined varies according to the duration of the thermal shock.