Showing papers by "University of Rennes published in 1994"

A highly conserved eukaryotic protein family possessing properties of polypeptide chain release factor

Abstract: THE termination of protein synthesis in ribosomes is governed by termination (stop) codons in messenger RNAs and by polypeptide chain release factors (RFs). Although the primary structure of prokaryotic RFs and yeast mitochrondrial RF is established1–4, that of the only known eukaryotic RF (eRF)5 remains obscure. Here we report the assignment of a family of tightly related proteins (designated eRFl) from lower and higher eukaryotes which are structurally and functionally similar to rabbit eRF. Two of these proteins, one from human6 and the other from Xenopus laevis7 , have been expressed in yeast and Escherichia coli, respectively, purified and shown to be active in the in vitro RF assay. The other protein of this family, sup45 (supl) of Saccharomyces cerevisiae, is involved in omnipotent suppression during translation8–12. The amino-acid sequence of the eRFl family is highly conserved. We conclude that the eRFl proteins are directly implicated in the termination of translation in eukaryotes.

Formulation and intestinal absorption enhancement evaluation of water-in-oil microemulsions incorporating medium-chain glycerides.

Abstract: We developed self-emulsifying water-in-oil (w/o) microemulsions incorporating medium-chain glycerides and measured their conductance, viscosity, refractive index and particle size. Formulation of Calcein (a water-soluble marker molecule, MW = 623), or SK&F 106760 (a water-soluble RGD peptide, MW = 634) in a w/o microemulsion having a composition of Captex 355/Capmul MCM/Tween 80/Aqueous (65/22/10/3, % w/w), resulted in significant bioavailability enhancement in rats relative to their aqueous formulations. Upon intraduodenal administration the bioavailability was enhanced from 2% for Calcein in isotonic Tris, pH 7.4 to 45% in the microemulsion and from 0.5% for SK&F 106760 in physiological saline to 27% in the microemulsion formulation. The microemulsion did not induce gross changes in GI mucosa at a dosing volume of 3.3 ml/kg. These results suggest that water-in-oil microemulsion systems may be utilized for enhancement of intestinal drug absorption.

Mineralogy, Chemistry, and Genesis of the Boninite Series Volcanics, Chichijima, Bonin Islands, Japan

Abstract: The Bonin archipelago represents an uplifted fore-arc terrain which exposes the products of Eocene supra-subduction zone magmatism. Chichijima, at the centre of the chain, represents the type locality for the high-Mg andesitic lava termed boninite. The range of extrusives which constitute the boninite series volcanics are present on Chichijima, and are disposed in the sequence boninite-andesite-dacite with increasing height in the volcano-stratigraphy. Progression to evolved compositions within the Chichijima boninite series is controlled by crystal fractionation from a boninite parental magma containing ? 15% MgO. Olivine and clinoenstatite are the initial liquidus phases, but extraction of enstatitic orthopyroxene, followed by clinopyroxene and plagioclase, is responsible for the general evolution from boninite, through andesite, to dacite. Some andesites within the overlying Mikazukiyama Formation are petrographically distinct from the main boninite series in containing magnetite phenocrysts and a high proportion of plagioclase. As such, these andesites have affinities with the calc-alkaline series. Major and trace element data for 74 boninitic series rocks from Chichijima are presented. Although major element variation is dominantly controlled by high-level crystal fractionation, the large variations in incompatiable trace element concentrations at high MgO compositions cannot be explained by this mechanism. Nd, Pb, and Sr isotopic data indicate the following: (1) a strong overprint on 87Sr/86Sr by seawater alteration; (2) Pb isotopes lie above the northern hemisphere reference line (NHRL) and are thus similar to the <30-Ma are and basin lavas of the Izu—Bonin system, and (3) ?Nd(40 Ma) ranges between 2.8 and 6.8 within the boninite series volcanics. Differences in rare-earth elements (REE), Zr, Ti, and 143Nd/144Nd at similar degrees of fractionation can be explained by the addition of a component of fixed composition from the down-going oceanic crustal slab to a variably depleted source region within the overlying wedge. Data presented for Sm/Zr and Ti/Zr indicate that boninite series volcanics are characterized by low values for both of these ratios. In particular, boninites appear to have uniquely low Sm/Zr ratios. These characteristics may be the result of slab melting in the presence of residual amphibole; the resultant melt could combine with typical slab dehydration fluids and infiltrate the overlying mantle wedge. Such a fluid—melt component could mix either with shallow mantle or directly with primitive melts from depleted mantle. Trace elements, REE, and isotope data thus point to a model for boninite genesis which requires tightly constrained pressure—temperature conditions in the slab combined with melting of a variably depleted source in the overlying wedge. Such constraints are rarely met except during the subduction of juvenile oceanic crust beneath a young, hot overriding plate.

Diets of Two Sympatric Colobines in Zaire: More Evidence on Seed-Eating in Forests on Poor Soils

Abstract: Recent studies have shown that the so- called folivorous African colobines eat a significant amount of seeds. There is disagreement as to whether seed-eating is due to the poor quality of tree foliage, due in turn to poor soils, or to the fact that seeds are a normal part of colobine diets. To test these hypotheses, we studied feeding of red colobus monkeys, Colobus badius tholloni,and black-and-white colobus monkeys, Colobus angolensis angolensis,in a tropical rain forest of Central Zaire (Salonga National Park). We conducted studies on soil properties, vegetation composition, and the availability and chemical contents of food plants simultaneously. Soils were very acid, with a high percentage of sand, very low cation exchange capacity, and very low exchangeable bases. The forest was dominated by legumes (45.6% of trees), among which the Caesalpinioideae were the best represented (85%). C. badiusfed mostly on leaves (61%) and seeds (33%), legumes making up 65% of their diet. C. angolensisfed mostly on seeds (50%) and leaves (27%); 39% of their diet came from legumes. The two species tended to select items richer in crude protein or lipids or both. Total phenolics and condensed tannins were abundant in the foliage and seeds but were poor predictors of colobine choice of food. Intersite comparisons show that colobines in Zaire ate a higher proportion of seeds than all other related species so far studied in Africa and that the Salonga forest had among the poorest soils and harbored the highest percentage of Caesalpinioideae. Our results confirm that seed- eating is more common among colobines living in areas where soils are poor. They strongly suggest that this link is mediated through forest composition, especially the abundance of legumes, and that the development of seed- eating results both from the high availability of nutrient-rich seeds and from the poor quality of mature tree foliage.

Identification of a lipolysis-stimulated receptor that is distinct from the LDL receptor and the LDL receptor-related protein

Abstract: This paper provides further characterization of a receptor that, in cells lacking the LDL receptor (FH fibroblasts), mediates lipoprotein binding, uptake, and degradation when incubated with oleate at concentrations not exceeding albumin binding capacity. This oleate-activated receptor is genetically distinct from the LDL receptor and is hereafter referred to as the lipolysis-stimulated receptor (LSR). Its apparent affinity was higher for triglyceride-rich lipoproteins (chylomicrons, VLDL) and for lipid emulsions supplemented with recombinant apoE, than for LDL which contains solely apoB. In contrast, VLDL isolated from a Type III hyperlipidemic patient (apoE2/2 phenotype) failed to bind to the LSR. Five lines of evidence indicated that the LSR is distinct from the LDL receptor-related protein (LRP): (1) the LRP ligand, alpha 2-macroglobulin-methylamine (alpha 2-MG*), did not bind to the oleate-induced LDL binding site; (2) oleate had no effect on the binding of alpha 2-MG* to LRP; (3) the LRP-associated protein, RAP, which inhibits LRP, had no effect on the LSR; (4) binding of lipoproteins to LSR was independent of Ca2+; and (5) LSR activity resolved as two proteins smaller than LRP (apparent molecular masses as determined by ligand blots: 115 and 85 kDa). That LSR provides a new candidate receptor contributing to the clearance of chylomicron remnants (CMR) is supported by the observation that LSR was inhibited by lactoferrin, a milk protein that delays CMR clearance when injected in vivo. Furthermore, in primary cultures of rat hepatocytes, oleate stimulated binding, uptake, and degradation of LDL with kinetic characteristics similar to that of LSR expressed in FH fibroblasts.(ABSTRACT TRUNCATED AT 250 WORDS)

Cloning, expression, and nucleotide sequence of genes involved in production of lactococcin DR, a bacteriocin from Lactococcus lactis subsp. lactis

Abstract: The partial nucleotide sequence of a Lactococcus lactis subsp. lactis ADRIA 85LO30 bacteriocin-producing operon was determined. The first two open reading frames of the operon are necessary to get bacteriocin expression in L. lactis IL1403R.

The importance of avian-contributed nitrogen (N) and phosphorus (P) to Lake Grand-Lieu, France

Abstract: The largest natural lake in France, Grand-Lieu, has suffered eutrophication. The objective of the study was to estimate the annual input of nutrients (N, P) resulting from avian excrement, deposited by birds feeding out of the lake and returning to its waters for breeding or roosting, as compared to the input by the rivers that enter in the lake. Two years are compared: 1981–82 and 1990–91. About 1600–2000 breeding herons and cormorants, 20000–33000 wintering ducks, gulls and cormorants and 1–2.4 million starlings deposited about 5800 kg total N in 1981–82 and 7640 kg in 1990–91. Respectively, 2000 and 2530 kg total P were deposited over the same time periods.These represent 0.7% and 0.4% of the total N input of the lake and 2.4 and 6.6% of the total P input in 1981–82 and 1990–91. Starlings account for 74% of the N and mallards most of the rest. P input by starlings (36% in 1981–82, 41% in 1990–91), and by mallards and herons (35% and 27% in 1981–82 and 22% and 24% in 1990–91 respectively) plays an appreciable role among birds. During the plant growing period (April-September), the contribution by birds can increase to 37% of total P input of the lake. Piscivorous bird colonies concentrate Phosphorus 42 times more within the colony than outside the colony. Overall, the role birds play in total N and P input is relatively small due to very high inputs from human sewage and agriculture run off. The monthly mean concentration of the water of the two rivers reaches currently 10 mg 1-1 of N (to 23 mg during peak floods) and 394 mg m-3 of P (to 468 mg during peak floods). Earlier, for example in the 1960’s, water in Brittany only contained 0.1 to 1.1 mg 1-1 of N and 1 to 5 mg m-3 of P during the maximum flow period. At this time, birds could probably have represented annually up to 37% of the N input and up to 95% of the P input to the lake.

Lactate and catecholamine responses in male and female sprinters during a Wingate test

Abstract: A total of six male and six female sprinters at the same national competition level and aged 18-20 years performed a force/velocity test and a 30-s supramaximal exercise test (Wingate test) on 2 different days, separated by a maximal interval of 15 days. The maximal anaerobic power (Wmax) was determined from the force/velocity test, and the mean anaerobic power (W) from the Wingate test. Immediately after the Wingate test, a 5-ml venous blood sample was drawn via a heparinized catheter in an antebrachial vein for subsequent catecholamine (adrenaline and noradrenaline) analysis. After 5 min recovery a few microliters of capillary blood were also taken for an immediate lactate determination. Even expressed per kilogram lean body mass, Wmax and W were significantly lower in women. The lactate and adrenaline responses induced by the Wingate test were also less pronounced in this group whereas the noradrenaline levels were not significantly different in men and women. Above all, very different relationships appeared between lactate, adrenaline, noradrenaline and W according to sex. Thus, as reported by other authors, the adrenergic response to a supramaximal exercise seemed to be lower in women than in men. Nevertheless a different training status between the two groups, even at same national competition level, could not be excluded and might contribute, at least in part, to the gender differences observed in the present study.

Lactic acid production from lactose in batch culture: analysis of the data with the help of a mathematical model; relevance for nitrogen source and preculture assessment

Abstract: Batch fermentation performances are usually optimized on the basis of an overall criterion, the mean volumetric productivity. For lack of more suitable criteria, a great number of experiments have to be carried out under various conditions, in order to identify the factors acting on product formation rate. With the help of a mathematical model, every batch fermentation is quantitatively described by a set of parameters, so the reason of every improvement observed for the fermentation productivity is easy to recognize. Therefore, such a model appears to be an invaluable tool for finding quickly and at lower expense the optimal conditions. Nitrogen supplementation and inoculum preparation for lactobacilli growing on whey and whey permeate have been assessed with the help of a new mathematical model.

Pipecolic acid is an osmoprotectant for Escherichia coli taken up by the general osmoporters ProU and Prop

Abstract: Exogenously supplied L-pipecolic acid was accumulated by Escherichia coli cells and protected them while growing at inhibitory osmolarity. Using specific uptake mutants and competitive assays, we established that the imino acid enters the cells through the ProP and ProU systems with K m values of 225 and 53 μM, respectively. Surprisingly, in spite of the requirement for the wild-type proX gene for osmoprotective ability, no binding activity of labelled pipecolate with the periplasmic protein encoded by proX could be detected. In an attempt to demonstrate whether the two porters (ProP and ProU) are the only carriers involved in osmoregulation, a variety of molecules known for their intracellular osmolarity-dependent accumulation in various organisms were investigated. N-Dimethylproline (proline betaine), N-dimethylglycine, homobetaine (β-alanine betaine), γ-butyrobetaine and dimethylsulfonio-propionate were found to be capable of promoting the growth of osmotically stressed E. coli. All of these molecules enter bacterial cells via ProP and ProU porters. None of the osmoprotectants except N-dimethylproline was able to bind the periplasmic protein encoded by proX, while this protein was necessary for their uptake. Apparently, ProP and ProU are the sole osmoporters involved in osmolyte influx into E. coli cells.

Intra- and interspecific host discrimination in two closely related egg parasitoids.

Abstract: Intraspecific host discrimination is frequently found in solitary parasitoids, but interspecific host discrimination, where female parasitoids recognize hosts already parasitized by females of other species, is rare. This particular behaviour appears to be adaptive only under specific circumstances. In this paper, we quantified intraspecific host discrimination in Anaphes n. sp. (Hymenoptera: Mymaridae), an endoparasitoid of the eggs of Listronotus oregonensis (LeConte) (Coleoptera: Curculionidae) and interspecific host discrimination toward eggs parasitized by Anaphes sordidatus (Girault), a sympatric species competing for the same resource in similar habitats. To examine host discrimination, choice experiments were used where the females had to choose between different categories of eggs (unparasitized, parasitized by Anaphes n. sp. or A. sordidatus). Superparasitism and multiparasitism were avoided in experiments where the female had a choice between unparasitized hosts and hosts parasitized by the same female, by a conspecific or by a female A. sordidatus. When all hosts available were parasitized, conspecific superparasitism occurred more often than self-superparasitism or multiparasitism. These results indicated that females Anaphes n. sp. were capable of self-, conspecific and interspecific discrimination. Self-discrimination followed recognition of an external marking while interspecific discrimination occurred mostly after insertion of the ovipositor. Interspecific discrimination could result from the recent speciation of these species and could be associated with a genotypic discrimination. This behavior appears to be adaptive because of the competition for common hosts between the two parasitoid species.

Influence of Nitrogen-content of a New Aluminophosphate Oxynitride Catalyst - Alpon in Knoevenagel Condensation

Abstract: A new high surface area solid basic catalyst with tunable acid-base properties has recently been proposed [R. Marchand, R. Conanec, Y. Laurent, Ph. Bastians, P. Grange, L.M. Gandia, M. Montes, J. Fernandes and I. Odriozola, patent application FR 940108 1; R. Conanec, R. Marchand, Y. Laurent, Ph. Bastians and P. Grange, in Soft Chemistry Routes to New Materials, Nantes, France, in press; P. Grange, Ph. Bastians, R. Conanec, R. Marchand and Y. Laurent, Chem. Commun., submitted for publication). Starting from aluminophosphate (AlPO4) oxide precursor and with careful adjustment of the nitridation procedure, it is possible to modify the global composition, changing the O/N content of the nitrided aluminophosphate (AlPON). This letter evidences that conversion in the malononitrile-benzaldehyde condensation largely depends on the O/N ratio of these new catalysts. Such basic solids are compared with conventional MgO catalyst.

The deadenylation conferred by the 3' untranslated region of a developmentally controlled mRNA in Xenopus embryos is switched to polyadenylation by deletion of a short sequence element.

Abstract: The maternal Xenopus Eg mRNAs are adenylated and translated in the mature oocyte and then, after fertilization, are deadenylated and released from polysomes. Therefore, after fertilization, a change occurs in the cellular mechanisms that control mRNA adenylation. In the study reported here, we show that the 3' untranslated region of Eg2 mRNA contains a cis-acting element that is required for the deadenylation of chimeric RNAs after fertilization. This cis-acting element is contained within a single 17-nucleotide portion of the Eg2 mRNA. Disruption of this deadenylation element allows adenylation of the chimeric transcripts in the embryo. Therefore, this cis-acting element is part of the sequence information required for the developmental switch from adenylation to deadenylation of the maternal Eg2 mRNA in Xenopus embryos.

Roughness of two-dimensional cracks in wood.

Abstract: Fractures in wood that are parallel to the fibers will be quasi-two-dimensional in the orthogonal directions. We have measured the roughness of fractures in Malaysian nemesu and Norwegian spruce wood. Tangential and radial fracture surfaces have very different morphologies due to the strong anisotropy of wood, but the scaling properties seem to be the same. We determine the roughness exponent $\ensuremath{\zeta}$ to be 0.68 \ifmmode\pm\else\textpm\fi{} 0.04, where the average is taken over different woods, fracture modes, and analyses. These results support the conjecture of a universal roughness exponent of brittle fracture surfaces.