Unexpected dimerization of a tripeptide comprising a β,γ‐diamino acid

We have previously reported the synthesis of enantiopure β,γ‐diamino acids and relevant short α/γ‐peptide containing such building blocks. Complete nuclear magnetic resonance (NMR) studies, together with molecular modeling, highlighted the ability of a β,γ‐diamino acid to induce various intramolecular turns. In this paper, we describe for the first time the formation of a dimeric structure constituted by α/γ/α‐tripeptide and stabilized by intermolecular interactions. A structural model is proposed based on extensive NMR measurements.     

Glycosylation reaction of unprotected sugars with hydroxyalkylthymine

Under mild conditions (Lewis acid/solvent/room temperature), the reaction of unprotected glucose, deoxyribose or xylose with hydroxylalkylthymine gives selectively nucleoside analogs with a spacer arm between sugar and base moiety. Experimental conditions (Lewis acid, solvent) for this new strategy leading to nucleoside analogs synthesis are discussed.     

Muscarinic M2 antagonists: anthranilamide derivatives with exceptional selectivity and in vivo activity

Anthranilamide analogues such as 23 are potent and highly selective muscarinic M2 antagonists that also show good oral bioavailability and in vivo activity.     

Spatio-temporal growth dynamics of a subAlpine Pinus uncinata stand in the French Alps

Natural forests are characterised by a high level of both spatial and temporal heterogeneity. The major processes involved in the creation and maintenance of forest heterogeneity in temperate climates are small-sized canopy disturbances. The resulting openings also modify the growth conditions for the remaining trees. The analysis of tree growth responses using dendrochronological techniques allows the reconstruction of the time sequence of the disturbances. The radial growth analysis is coupled here with both a spatial analysis and a demographic analysis of the forest structure. The age classes are temporally organised in cohorts and spatially distributed in spatial aggregates. The analysis of the most documented disturbance event allowed us to determine the size of the disturbance response patch (between 0.036 and 0.073 ha) and the duration of the disturbance (six years). We considered that this small-scale disturbance event may have been caused by the fall of a single tree and has freed the surrounding trees of its competition.     

Engineering tolerance and accumulation of lead and cadmium in transgenic plants

We have studied the utility of the yeast protein YCF1, which detoxifies cadmium by transporting it into vacuoles, for the remediation of lead and cadmium contamination. We found that the yeast YCF1-deletion mutant DTY167 was hypersensitive to Pb(II) as compared with wild-type yeast. DTY167 cells overexpressing YCF1 were more resistant to Pb(II) and Cd(II) than were wild-type cells, and accumulated more lead and cadmium. Analysis of transgenic Arabidopsis thaliana plants overexpressing YCF1 showed that YCF1 is functionally active and that the plants have enhanced tolerance of Pb(II) and Cd(II) and accumulated greater amounts of these metals. These results suggest that transgenic plants expressing YCF1 may be useful for phytoremediation of lead and cadmium.     

Light scattering studies of the solution properties of chitosans of varying degrees of acetylation

The use of two techniques, differential interferometry and quasi-elastic light scattering (QELS), allowed us to study solutions of chitosan varying in degree of acetylation (DA), degree of dissociation (alpha), and concentration (C(p)). With the first technique, we demonstrated the modification of the electric polarizability of the polymer chains, through a law of behavior of the variation of the refractive index increment dn/dC with DA and alpha. This brought us information on the various kinds of interactions (H-bonds, electrostatic, and hydrophobic) involved in the evolution of the solution properties. QELS experiments performed in dilute regime showed the presence of supramolecular structures depending on DA and alpha. The topology and the nature of these objects are discussed. The typical presence of aggregates and their evolution with concentration was also demonstrated in semidilute regime.     

Acute inflammation increases selective uptake of HDL cholesteryl esters into adrenals of mice overexpressing human sPLA2

The acute-phase protein secretory phospholipase A2 (sPLA2) influences the metabolism of high-density lipoproteins (HDL). The adrenals are known to utilize HDL cholesterol as a source of sterols. The aim of the present study was to test the hypothesis that sPLA2 enhances the selective uptake of HDL into the adrenals in response to acute inflammation as a possible physiological role for the sPLA2-HDL interaction. Human sPLA2-transgenic mice, in which sPLA2 expression is upregulated by inflammatory stimuli, were used. Ten hours after induction of the acute-phase response (APR) by injection of bacterial lipopolysaccharide (LPS), plasma levels of HDL cholesterol decreased significantly in sPLA2-transgenic mice (-18%, P < 0.05) but remained unchanged in wild-type mice. The fractional catabolic rates of both 125I-labeled tyraminecellobiose (TC)-HDL and [3H]cholesteryl ether increased significantly in the sPLA2-transgenic mice after induction of the APR (0.18 +/- 0.01 vs. 0.21 +/- 0.01 pool/h, P < 0.05, and 0.31 +/- 0.02 vs. 0.42 +/- 0.05 pool/h, P < 0.05, respectively) but remained unchanged in the wild-type mice (0.10 +/- 0.01 vs. 0.22 +/- 0.02 pool/h, respectively). After induction of the APR, in both groups HDL holoparticle uptake by the liver was increased (P < 0.001). sPLA2-transgenic mice had 2.4-fold higher selective uptake into the adrenals after induction of the APR than wild-type mice (156 +/- 6 vs. 65 +/- 5%/ micro g tissue protein, P < 0.001). In summary, upregulation of sPLA2 expression during the APR specifically increases the selective uptake of HDL cholesteryl ester into the adrenals. These data suggest a novel metabolic role for sPLA2: modification of HDL during the APR to promote increased adrenal uptake of HDL cholesteryl ester to serve as source for steroid hormone synthesis.     

The ageing phenomenon of turbot spermatozoa: effects on morphology, motility and concentration, intracellular ATP content, fertilization, and storage capacities

The deleterious effect of the ageing phenomenon of turbot spermatozoa was investigated in relation to the sampling date. Spermatozoa with a low or highly condensed chromatin and a middle piece containing numerous or a few vesicles were observed simultaneously 80 and 47 days before the beginning of the spawning period of the females. The middle piece of spermatozoa contained few vesicles, 39 days after the end of the reproductive period. At the same date, some spermatozoa appeared in which the plasma membrane was broken. Sperm motility, assessed just after collection in terms of arbitrary motility scores from 0 to 5, was significantly increased both at 10 and 60 s post-activation, for samples collected 18 days after, 25 days before and 9 days after the beginning of the spawning period of the females, respectively compared to samples collected 6 days before, 55 days after and 88 days after the end of this period. A lower short-term storage capacity was recorded at 10 and 60 s post-activation for sperm samples collected 6 days before and 88 days after the end of the reproductive period, respectively compared to 18 days and 9 days after the beginning of the spawning period. At 60 s post-activation, a higher motility of thawed spermatozoa was observed for samples collected 5 days before the beginning of the spawning period (motility recovery index: 86.4 ± 19.4%) compared to 71 days after the end of this period (55.0 ± 12.0%). The fertilizing capacity of sperm samples collected 61 days after the end of the spawning season (66.1 ± 14.6%) was significantly lower than that recorded for samples collected 34 days after the beginning of the spawning period (75.2±9.6%). On the contrary, there was no significant decrease in endogenous ATP content (31 days after the beginning of the spawning period, 14.53 ± 0.84; 48 days after the end of this period, 10.75 ± 5.26 nmol 10^{? 8} spermatozoa). Furthermore, sperm concentration significantly increased between the same dates (respectively 3.3 ± 0.8–9.4±4.8×10⁹ spermatozoa ml^?1).     

Biochemical and morphological changes in the chorion of the carp (Cyprinus carpio) oocyte, following the cortical reaction

Following oviposition and/or fertilization in fieshwater, the soft vitelline membrane surrounding the carp oocyte elevates and becomes tough (fertilization envelope). We have studied the biochemical (protease digestion) and morphological (analysis scanning electron microscopy) changes associated with this transformation. The vitelline envelope is easily digested by most proteolytic enzymes; following elevation, the chorion becomes very resistant to proteolyse. This chorion is much thinner and smoother than the vitelline membrane, but retains a characteristic porous appearance. These results are compared with previous observations obtained by transmission electron microscopy and are discussed in relation to the blockage to polyspermy.