Étude expérimentale de l'auto-association des molécules modèles dipeptidiques. II. Association stéréosélective des molécules énantiomères

Modes of aggregation fo alanine-, norvaline- and valine-contaiing dpepetides with the general formula R₁? C₁O₁? N₂H₂? CHR₂? C₂O₂? N₃H₃? R₃ have been studied in CCl₄ solution by using infrared and nuclear magnetic resonance spectroscopies. Solutions of the pure L isomer and of the racemic mixture do not give identical data. At a given concentration, the racemic mixtrue is more aggregated than the pure enantiomer, and the difference, negligible in the case of alanine derivative, increases wiht the bulkiness of the side cahin R₂. The results show that a selective interaction takes place between enantiomeric molecules, resulting ina dimer associating tow inverse configurated C₅ conformers. The stabilizaion of this dimer proceeds from two symmetrical and intermolecular H₃ … O₁ hydrogen bondings.     

Tumor necrosis factor alpha − 308G>A, − 863C>A, − 857C>T gene polymorphisms and tuberculosis susceptibility: A meta-analysis

Background/aims

A large number of studies have shown that polymorphisms in the tumor necrosis factor-α (TNF-α, TNFA) gene are implicated in susceptibility to tuberculosis (TB). However, the results are inconsistent. We performed this meta-analysis to estimate the association between polymorphisms in the TNFA gene and TB susceptibility.

Methods

Relevant studies published before March 2012 were identified by searching PubMed, ISI web of knowledge, EBSCO and CNKI. The strength of relationship between the TNFA gene and TB susceptibility was assessed using odds ratios (ORs).

Results

A total number of twenty-three case–control studies including 3630 cases and 4055 controls were identified referring to three previously chosen single-nucleotide polymorphisms (SNPs): − 308G>A, − 863C>A and − 857C>T. No association was found between − 308G>A, − 863C>A and TB susceptibility: − 308G>A (GG + GA vs. AA): OR 0.85, 95%CI: 0.55–1.30, P = 0.44; − 863C>A (CC + CA vs. AA): OR 0.93, 95%CI: 0.84–1.81, P = 0.83. Increased risk of TB was associated with − 857C>T in the dominant genetic model (CC + CT vs. TT: OR 2.13, 95%CI: 1.25–3.63, P = 0.01), the heterozygote comparison (CT vs. TT: OR 2.69, 95%CI: 1.44–5.02, P = 0.00) and the homozygote comparison (CC vs. TT: OR 2.08, 95%CI: 1.22–3.53, P = 0.01) in Asian subjects.

Conclusion

There is an increased association between TNFA − 857C>T polymorphism and TB risk among Asian subjects. No association was found between − 308G>A and − 863C>A with TB risk. Due to several limitations in the present study, well-designed epidemiological studies with large sample size among different ethnicities should be performed in the future.     

A de novo (1;2;3;15;18) chromosome rearrangement with six nonreciprocal translocations

A de novo complex chromosome rearrangement (CCR) found in a phenotypically abnormal boy was characterized by G-bands, FISH with subtelomere probes, and M-FISH. The G-banding analysis revealed involvement of chromosomes 1, 2, 3, 15, and 18 with (at least) eight breakpoints, five nonreciprocal translocations (1q --> 2q --> 8q --> 15q --> 2p --> 1q), and a 3p insertion into the der(2); there was also a presumptive deletion of 1q41. The 5 derivatives were described as follows: der(1)(1pter --> 1q32.3?::2p21--> 2pter),der(2)(1qter --> 1q42?::2q24.2 --> 2p21::3p13 --> 3p26::15q15 --> 15qter),der(3)(3qter --> 3p13:),der(15)(15pter --> 15q15::18q11 --> 18qter),der(18)(18pter --> 18q11::2q24.2 --> 2qter). The molecular assays confirmed the segmental composition of each derivative and documented the localization of most relevant telomeres. In addition to the novelty of the 1, 2, 3, 15 and 18 combination, this CCR may also be unique in the sense that it represents a cluster of 6 nonreciprocal transpositions regardless of the occurrence (or lack thereof) of secondary unbalances. Finally, there appears to be an excess of CCRs in fetuses conceived by intracytoplasmic sperm injection.     

Effects of CO2-HCO<SUP>&minus;</SUP><SUB>3</SUB> on catecholamine efflux from cat carotid body

Iturriaga, Rodrigo, and Julio Alcayaga. Effects ofCO₂-on catecholamine efflux from cat carotid body. J. Appl. Physiol. 84(1): 60-68, 1998.Using achronoamperometric technique with carbon-fiber microelectrodes andneural recordings, we simultaneously measured the effects of thefollowing procedures on catecholamine efflux (CA) andfrequency of chemosensory discharges (f_x) fromsuperfused cat carotid body: 1) theaddition ofCO₂- to Tyrode solution previously buffered withN-2-hydroxyethylpiperazine-N -2-ethanesulfonicacid, maintaining pH at 7.40; 2)hypercapnia (10% CO₂, pH 7.10);3) hypoxia(PO₂ h  40 Torr) with andwithoutCO₂-;and 4) the impact of several bolusesof dopamine (DA; 10-100 µg) on hypoxic and hypercapnic challenges. WithCO₂-,hypoxia increased f_x which preceded CAincreases, whereas hypercapnia raised f_x but didnot consistently increase CA. Repeated stimuli induced similarf_x increases, but attenuated CA. AfterDA, hypoxia produced larger CA, which preceded chemosensoryresponses. WithoutCO₂-, hypoxia produced a similar pattern of CA andf_x responses. Switching to Tyrode solution withCO₂-at pH 7.40 raised f_x but did not increase CA.WithCO₂- and after DA, hypoxic-induced CAs were larger than in its absence. Results suggest that DA release is not essential for chemosensory excitation.

     

The C : N : P stoichiometry of autotrophs – theory and observations

Evolution has set biochemical constraints on the chemical composition of living organisms. These constraints seem to lead to increases in N : C and P : C ratios with increasing relative growth rate for all types of organisms. The N : P ratio also seems to decrease with relative growth rate for heterotrophs whereas autotrophs may show a more complex behaviour. Here I will show that, from biochemical considerations, N : C should increase linearly and P : C quadratically with relative growth rate in autotrophs with the consequence that N : P increases at low relative growth rates, passes a maximum and then decreases at high relative growth rates. These predictions are verified against observations for a freshwater alga (Selenastrum minutum) and a tree seedling (Betula pendula). Changes in temperature, light or other factors that affect the growth rate of autotrophs interact with nutrient supply in such a way that there are no simple rules for as to how N : P will change.     

Biological control of the citrus red mite <Emphasis Type="Italic">Panonychus</Emphasis><Emphasis Type="Italic">citri</Emphasis> by the predator mite <Emphasis Type="Italic">Typhlodromus athiasae</Emphasis> on two citrus cultivars under greenhouse conditions

This study examined the efficacy of the predatory mite Typhlodromus athiasae Porath and Swirski (Acari: Phytoseiidae) as a biological control agent of the citrus red mite Panonychus citri (McGregor) (Acari: Tetranychidae) on seedlings of Washington and Valencia citrus cultivars at 1:10, 1:20 and 1:40 predator:prey release ratios under greenhouse conditions. At predator:prey ratios of 1:10, significant reductions on P. citri populations were observed one week after release of T. athiasae, and populations remained at low levels thereafter. The highest mean numbers of P. citri were found in the third week on the Washington cultivar and in the fourth week on Valencia, in a control group with no predators. This study demonstrates the potential of T. athiasae to effectively control P. citri on Washington and Valencia cultivars under greenhouse conditions at predator:prey ratios of 1:10. However, T. athiasae was unable to control the citrus red mite populations when the predator:prey ratio was reduced to 1:40. We therefore recommend a release ratio of 1:10 for effective control of P. citri in greenhouses on seedlings of Washington and Valencia citrus.     

Unexpected reversal of the regioselectivity in <Emphasis Type="Italic">Thermomyces lanuginosus</Emphasis> lipase-catalyzed acylation of floxuridine

Unexpected inversion of the 3′:5′-regioselectivity was observed in the enzymatic methacryloylation, crotonylation and cinnamoylation of floxuridine (1.5:1, 2.3:1 and 4.4:1, respectively), where Thermomyces lanuginosus lipase preferentially catalyzed the acylation of 3′-hydroxyl rather than that of 5′-hydroxyl group. The possible reason might be the presence of a remote interaction between the unsaturated bond in the acyl group and the aromatic ring of amino acid residue Trp89 in the lid of the lipase. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Seroprevalence of <Emphasis Type="Italic">Coxiella burnetii</Emphasis> antibodies among students of the <Emphasis Type="Italic">Faculty of Medicine</Emphasis> in Košice (Slovakia)

Titers of immunoglobulin IgG against phases I and II of Coxiella burnetii were determined in 241 students of the Faculty of Medicine by ELISA method and the respective risk factors were evaluated, e.g., rural and urban life, consumption of milk, contact with animals and gender, which may be associated with exposure to C. burnetii. Phase I antibodies (Abs) were detected in 59 serum samples (24.4 %) at antibody level of 1: 100–1: 400. Phase II Abs were found in 179 persons (74.2 %). The titers were in the range of 1: 100–1: 1600. The titer ≥1: 800 of IgG was used as a cut-off level, and was detected only in 20 students (8.2 %). No significant difference in the prevalence of Abs was detected either between the students living in rural and urban environment (78.8 and 73.2 %, respectively) or between males and females (74.0 and 74.7 %, respectively). Abs were detected more frequently in raw milk consumers (68.1 %) and in students who kept some animals (73.7 %).     

High‐frequency fire alters C : N : P stoichiometry in forest litter

Fire is a major driver of ecosystem change and can disproportionately affect the cycling of different nutrients. Thus, a stoichiometric approach to investigate the relationships between nutrient availability and microbial resource use during decomposition is likely to provide insight into the effects of fire on ecosystem functioning. We conducted a field litter bag experiment to investigate the long‐term impact of repeated fire on the stoichiometry of leaf litter C, N and P pools, and nutrient‐acquiring enzyme activities during decomposition in a wet sclerophyll eucalypt forest in Queensland, Australia. Fire frequency treatments have been maintained since 1972, including burning every 2 years (2yrB), burning every 4 years (4yrB) and no burning (NB). C : N ratios in freshly fallen litter were 29–42% higher and C : P ratios were 6–25% lower for 2yrB than NB during decomposition, with correspondingly lower 2yrB N : P ratios (27–32) than for NB (34–49). Trends in litter soluble and microbial N : P ratios were similar to the overall litter N : P ratios across fire treatments. Consistent with these, the ratio of activities for N‐acquiring to P‐acquiring enzymes in litter was higher for 2yrB than NB, whereas 4yrB was generally intermediate between 2yrB and NB. Decomposition rates of freshly fallen litter were significantly lower for 2yrB (72 ± 2% mass remaining at the end of experiment) than for 4yrB (59 ± 3%) and NB (62 ± 3%), a difference that may be related to effects of N limitation, lower moisture content, and/or litter C quality. Results for older mixed‐age litter were similar to those for freshly fallen litter although treatment differences were less pronounced. Overall, these findings show that frequent fire (2yrB) decoupled N and P cycling, as manifested in litter C : N : P stoichiometry and in microbial biomass N : P ratio and enzymatic activities. Furthermore, these data indicate that fire induced a transient shift to N‐limited ecosystem conditions during the postfire recovery phase.     

Plasmonic Au-MoO<Subscript>3</Subscript> Colloidal Nanoparticles by Reduction of HAuCl<Subscript>4</Subscript> by Blue MoO<Subscript>x</Subscript> Nanosheets and Observation of the Gasochromic Property

Defective colloids of blue MoO_x nanosheets were prepared by anodizing exfoliation method in water. This colloidal solution exhibits an optical plasmonic absorption band in the infrared region at about 760 nm. Merely mixing HAuCl₄ solution with the MoO_x leads to loss of the blue color, decaying of 760 nm plasmonic peak and simultaneous formation of the gold plasmon absorption peak at 550–570 nm. Some spectral variations in gold plasmonic peak and MoO_x optical band gap were observed for Mo:Au ratio of 10:1, 20:1, 30:1, and 40:1. The size of the gold nanoparticles was in the 5–6 nm range with fcc crystalline structure. X-ray photoelectron spectroscopy (XPS) revealed that the initial solution contains Mo⁵⁺ states and hydroxyl groups, which after reduction, hydroxyl groups are eliminated and the Mo⁵⁺ states converted to Mo⁶⁺. The obtained Au-MoO₃ colloids have a gasochromic property in which they are colored back to blue in the presence of hydrogen gas and the molybdenum oxide absorption peak recovered again. Furthermore, it was observed that both gold and Mo oxide plasmonic peaks redshift by insertion of hydrogen gas which is attributed to change in solution refractive index and formation of defect concentration.     

Characterization of <Emphasis Type="Italic">Fusarium graminearum</Emphasis> inhibitory lipopeptide from <Emphasis Type="Italic">Bacillus subtilis</Emphasis> IB

Bacillus subtilis strain IB exhibiting inhibitory activity against the Fusarium head blight disease fungus Fusarium graminearum was isolated and identified. The major inhibitory compound was purified from the culture broth through anion exchange, hydrophobic interaction, and reverse phase high-performance liquid chromatography (RP-HPLC) steps. It was a 1,463-Da lipopeptide and had an amino acid composition consisting of Ala, Glx, Ile, Orn, Pro, Thr, and Tyr at a molar ratio of 1:3:1:1:1:1:2. Electrospray ionization mass spectrometry/mass spectrometry (ESI MS/MS) analyses of the natural and the ring-opened peptides showed the antagonist was fengycin, a kind of macrolactone molecule with antifungal activity produced by several Bacillus strains. Fluorescence microscopic analysis indicated this peptide permeabilized and disrupted F. graminearum hyphae.     

Structural elements of the C-terminal domain of subunit E (E<Subscript>133-222</Subscript>) from the <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> V<Subscript>1</Subscript>V<Subscript>O</Subscript> ATPase determined by solution NMR spectroscopy

Subunit E of the vacuolar ATPase (V-ATPase) contains an N-terminal extended α helix (Rishikesan et al. J Bioenerg Biomembr 43:187–193, 2011) and a globular C-terminal part that is predicted to consist of a mixture of α-helices and β-sheets (Grüber et al. Biochem Biophys Res Comm 298:383–391, 2002). Here we describe the production, purification and 2D structure of the C-terminal segment E_133-222 of subunit E from Saccharamyces cerevisiae V-ATPase in solution based on the secondary structure calculation from NMR spectroscopy studies. E_133-222 consists of four β-strands, formed by the amino acids from K136-V139, E170-V173, G186-V189, D195-E198 and two α-helices, composed of the residues from R144-A164 and T202-I218. The sheets and helices are arranged as β1:α1:β2:β3:β4:α2, which are connected by flexible loop regions. These new structural details of subunit E are discussed in the light of the structural arrangements of this subunit inside the V₁- and V₁V_O ATPase.     

L'école de la périphérie: Scolarité et ségrégation en banlieue

L'école de la périphérie: Scolarité et ségrégation en banlieue. Agnès van Zanten. Presses Universitaires de France, 2001. 424 pp.     

Optimal design of the Wilcoxon–Mann–Whitney‐test

In scientific research, many hypotheses relate to the comparison of two independent groups. Usually, it is of interest to use a design (i.e., the allocation of sample sizes m and n for fixed ) that maximizes the power of the applied statistical test. It is known that the two‐sample t‐tests for homogeneous and heterogeneous variances may lose substantial power when variances are unequal but equally large samples are used. We demonstrate that this is not the case for the nonparametric Wilcoxon–Mann–Whitney‐test, whose application in biometrical research fields is motivated by two examples from cancer research. We prove the optimality of the design in case of symmetric and identically shaped distributions using normal approximations and show that this design generally offers power only negligibly lower than the optimal design for a wide range of distributions.     

Zein accumulation in forage species (<Emphasis Type="Italic">Lotus corniculatus</Emphasis> and <Emphasis Type="Italic">Medicago sativa</Emphasis>) and co-expression of the γ-zein:KDEL and β-zein:KDEL polypeptides in tobacco leaf

Plants of birdsfoot trefoil (Lotus corniculatus), alfalfa (Medicago sativa) and tobacco (Nicotiana tabacum) were transformed by Agrobacterium with binary vectors harbouring genes that code either for wild-type and %-zein:KDEL, or for #-zein:KDEL. The maize seed storage proteins %-zein and #-zein are rich in sulphur amino acids, and our long-term goal is to improve alfalfa and birdsfoot trefoil forage quality. Significant levels of zeins were detected in leaves of birdsfoot trefoil transformants, ranging up to 0.055% and 0.30% of total extractable protein for %-zein and #-zein:KDEL, respectively. In leaves of alfalfa, the %-zein:KDEL expression level was up to 0.026% of the total extractable protein. From a F₁ population of transgenic tobacco, a plant was selected in which the amount of zeins (%-zein:KDEL plus #-zein:KDEL) accounted for 1.1% of the total extractable protein.     

<Emphasis Type="Italic">In vitro</Emphasis> inhibitory effect of cranberry (<Emphasis Type="Italic">Vaccinium macrocarpum</Emphasis> Ait.) juice on pathogenic microorganisms

The purpose of this study was to determine the inhibitory effects of cranberry juice on pathogenic microorganisms. The microorganisms analyzed were Escherichia coli from patients with urinary infections, Salmonella spp., Listeria monocytogenes, Pseudomona aeruginosa, and Staphylococcus aureus. The disc method was used to determine the sensitivity of bacteria to cranberry juice (CJ, both concentrated and diluted). A lawn of 10⁶ cfu/ml was grown on agar surfaces in Petri dishes and on Whatman discs that had been previously saturated with CJ and CJ : water. 1 : 1 to 1 : 50 juice solutions had been placed on the discs, which were cultured and incubated. The results indicated that S. aureus was more susceptible to cranberry juice inhibition than the other microorganisms. L. monocytogenes was the most resistant to the inhibitory action of cranberry juice, showing a significant difference from the inhibition of P. aeruginosa, uropathogenic E. coli, Salmonella spp., and S. aureus. This study also demonstrated that the inhibitory activity of cranberry juice for E. coli took place up to a dilution of 1 : 20. Published in Russian in Prikladnaya Biokhimiya i Mikrobiologiya, 2008, Vol. 44, No. 3, pp. 333–336. The text was submitted by the authors in English.     

C : N : P stoichiometry of dominant riparian trees and arthropods along the Middle Rio Grande

1. We examined the role of flooding on the leaf nutrient content of riparian trees by comparing the carbon : nitrogen : phosphorus (C : N : P) ratio of leaves and litter of Rio Grande cottonwood (Populus deltoides ssp. wislizenii) in flood and non‐flood sites along the Middle Rio Grande, NM, U.S.A. The leaf C : N : P ratio was also examined for two non‐native trees, saltcedar (Tamarix chinensis) and Russian olive (Elaeagnus angustifolia), and six species of dominant riparian arthropods. 2. Living leaves and leaf litter of cottonwoods at flood sites had a significantly lower leaf N : P ratio and higher %P compared with leaves and litter at non‐flood sites. A non‐flood site downstream from wastewater effluent had a significantly lower litter C : N ratio than all other sites, suggesting N fertilisation through ground water. The non‐native trees, saltcedar and Russian olive, had higher mean leaf N content, N : P ratio, and lower C : N ratio compared with cottonwoods across study sites. 3. Riparian arthropods ranged from 5.2 to 7.1 for C : N ratio, 56–216 for C : P ratio, and 8.9–34 for N : P ratio. C content ranged from 25 to 52% of dry mass, N content from 4.7 to 10.8%, and P content from 0.59 to 1.2%. Differences in stoichiometry between high C : nutrient leaf litter and low C : nutrient invertebrates suggests possible food‐quality constraints for detritivores. 4. These results suggest that spatial and temporal variation in the C : N : P ratio of cottonwood leaves and leaf litter is influenced by surface and subsurface hydrologic connection within the floodplain. Reach‐scale variation in the elemental composition of riparian organic matter inputs may have important implications for decomposition, nutrient cycling, and food webs in river floodplain systems.     

Life cycle of <Emphasis Type="Italic">Aylax hypecoi</Emphasis> (<Emphasis Type="Italic">Insecta: Hymenoptera: Cynipidae</Emphasis>), a gall inducer on <Emphasis Type="Italic">Hypecoum</Emphasis> ssp. (<Emphasis Type="Italic">Papaveraceae</Emphasis>)

The life cycle and developmental stages of Aylax hypecoi (Trotter, 1913, Hymenoptera: Cynipidae: Aylacini) were studied in detail. Aylax hypecoi is known to induce galls in fruits of two Hypecoum species — H. imberbe and H. geslini (Papaveraceae) and the larva develops in host plant fruits. The morphology and development of egg, larva and pupa were investigated, which has previously not been done. The shape and size of terminal-instar larvae and associated galls are sex-specific. Overwintering stage, adult emergence and flying periods, and egg productivity were studied also.