Characterisation of pectin subunits released by an optimised combination of enzymes

Pectins from sugar beet, lime and apple were degraded by a rhamnogalacturonan hydrolase associated or not with pectin methylesterases and side chain degrading enzymes (galactanase and arabinanase). The composition of the enzymatic mixture was optimised by following the reaction by viscosimetric means. The reaction products were fractionated by ion exchange chromatography. Treatment with all the enzymes released four fractions: (1). 227-247 mg/g of initial pectins and corresponded to neutral sugars from the side chains; (2,3). represented together 184-220 mg/g of pectins and corresponded to rhamnogalacturonan; (4). 533-588 mg/g of pectins and corresponded to homogalacturonan. Lime pectins have the shortest rhamnogalacturonan regions. The molar masses of homogalacturonans were in the range of 16000-43400 g/mol according to the origin of pectins, corresponding to degrees of polymerisation of 85-250. The mode of action of the enzymes used is also discussed.     

Ventilatory support: a dynamical systems approach

Misunderstanding of the dynamical behavior of the ventilatory system, especially under assisted ventilation, may explain the problems encountered in ventilatory support monitoring. Proportional assist ventilation (PAV) that theoretically gives a breath by breath assistance presents instability with high levels of assistance. We have constructed a mathematical model of interactions between three objects: the central respiratory pattern generator modelled by a modified Van der Pol oscillator, the mechanical respiratory system which is the passive part of the system and a controlled ventilator that follows its own law. The dynamical study of our model shows the existence of two crucial behaviors, i.e. oscillations and damping, depending on only two parameters, namely the time constant of the mechanical respiratory system and a cumulative interaction index. The same result is observed in simulations of spontaneous breathing as well as of PAV. In this last case, increasing assistance leads first to an increase of the tidal volume (V_T), a further increase in assistance inducing a decrease in V_T, ending in damping of the whole system to an attractive fixed point. We conclude that instabilities observed in PAV may be explained by the different possible dynamical behaviors of the system rather than changes in mechanical characteristics of the respiratory system.     

Effects of territorial intrusions, courtship feedings and mate fidelity on the copulation behaviour of the osprey

We studied copulation behaviour of the osprey, Pandion haliaetus, a semicolonial, fish-eating raptor, in Corsica (Mediterranean). Pairs copulated over a long period (45 days) and at a high rate, with, on average, 288 within-pair copulations (WPCs) for a clutch. Pairs breeding at higher density faced more frequent territorial intrusions than others and were potentially at an increased cuckoldry risk. However, and contrary to predictions of the ‘paternity assurance’ hypothesis for frequent copulations, we found that WPC rate decreased with increasing frequency of territorial intrusions. Male territory attendance increased with territorial intrusion frequency, to the detriment of the food provisioning of the female. Both attempted and successful WPC rates were positively related to the amount of food delivered by the male. Thus, the more frequent the territorial intrusions, the more time the male spent within his territory, the less he courtship fed and the smaller the fish he delivered, and the less the pair copulated successfully. WPC rate was also higher in newly formed pairs than in established pairs, and decreased with increasing pair bond length. The results suggest that males rely on mate guarding rather than frequent copulations to ensure paternity, and do not support the idea that sperm competition is the main cause of frequent WPCs. Nonfertilization functions of frequent copulations, such as pair bonding, mate assessment and mate retention, were likely early in the prelaying period. The findings that WPC rate decreased with mate fidelity and that females traded copulations for food suggest that mate retention was a possible function of frequent copulations in this species. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Phosphoinositide-dependent kinase phosphorylation of protein kinase C Apl II increases during intermediate facilitation in aplysia

Phosphorylation of protein kinase Cs (PKCs) by phosphoinositide-dependent kinase I (PDK) is critical for PKC activity. In the nervous system of the marine mollusk Aplysia, there are only two major PKC isoforms, the calcium-activated PKC Apl I and the calcium-independent PKC Apl II, and both PKCs are persistently activated during intermediate memory. We monitored the PDK-dependent phosphorylation of PKC Apl I and PKC Apl II using phosphopeptide antibodies. During persistent activation of PKCs in Aplysia neurons, there is a significant increase in the amount of PDK-phosphorylated PKC Apl II in the particulate fraction but no increase in the amount of PKC Apl I phosphorylated by PDK. PDK phosphorylation of PKCs was not sensitive to inhibitors of phosphatidylinositol 3-kinase, PKC, or expression of a kinase-inactive PDK. Localization of PDK-phosphorylated PKC Apl II using immunocytochemistry revealed an enrichment of phosphorylated PKC Apl II at the plasma membrane. These data suggest that increased PDK phosphorylation of PKC Apl II is important for persistent kinase activation.     

FTIR and UV spectroscopy studies of triplex formation between alpha-oligonucleotides with non-ionic phoshoramidate linkages and DNA targets

The triplexes formed by pyrimidine alpha-oligodeoxynucleotides, 15mers alpha dT(15) or 12mers alpha dCT having dimethoxyethyl (PNHdiME), morpholino (PMOR) or propyl (PNHPr) non-ionic phosphoramidate linkages with DNA duplex targets have been investigated by UV and FTIR spectroscopy. Due to the decrease in the electrostatic repulsion between partner strands of identical lengths all modifications result in triplexes more stable than those formed with unmodified phosphodiester beta-oligodeoxynucleotides (beta-ODNs). Among the alpha-ODN third strands having C and T bases and non-ionic phosphoramidate linkages (alpha dCTPN) the most efficient modification is (PNHdiME). The enhanced third strand stability of the alpha dCTPN obtained as diastereoisomeric mixtures is attenuated by the steric hindrance of the PMOR linkages or by the hydrophobicity of the PNHPr linkages. All alpha dCTPN strands form triplexes even at neutral pH. In the most favorable case (PNHdiME), we show by FTIR spectroscopy that the triplex formed at pH 7 is held by Hoogsteen T*A.T triplets and in addition by an hydrogen bond between O6 of G and C of the third strand (Tm = 30 degrees C). The detection of protonated cytosines is correlated at pH 6 with a high stabilization of the triplex (Tm = 65 degrees C). While unfavorable steric effects are overcome with alpha anomers, the limitation of the pH dependence is not completely suppressed. Different triplexes are evidenced for non pH dependent phosphoramidate alpha-thymidilate strands (alpha dT(15)PN) interacting with a target duplex of identical length. At low ionic strength and DNA concentration we observe the binding to beta dA(15) either of alpha dT(15)PN as duplex strand and beta dT(15) as third strand, or of two hydrophobic alpha dT(15)PNHPr strands. An increase in the DNA and counterion concentration stabilizes the anionic target duplex and then the alpha dT(15)PN binds as Hoogsteen third strand.     

Age-dependent material properties of the porcine cerebrum: effect on pediatric inertial head injury criteria

During growth and development, the immature central nervous system undergoes rapid alterations in constituents and structure. We hypothesize that these alterations are accompanied by changes in the mechanical properties of brain tissue which, in turn, influence the response of the brain to traumatic inertial loads. Samples of frontal cerebrum from neonatal (2–3 days) and adult pigs were harvested and tested within 3 h post-mortem. The complex shear modulus of the samples was measured in a custom-designed oscillatory shear testing device at engineering shear strain amplitudes of 2.5% or 5% from 20–200 Hz, at 25°C and 100% humidity. In this range, the elastic and viscous components of the complex shear modulus increased significantly with the development of the cerebral region of the brain. Using an idealized model of the developing head, the age-dependent material properties of brain tissue were shown to affect the mechanical response of the brain to inertial loading. This study is a first step toward developing head injury tolerance criteria specifically for the pediatric population.     

Improvement of the binding capacity of metal cations by sugar-beet pulp. 2. Binding of divalent metal cations by modified sugar-beet pulp

Binding of some divalent cations (Ca²⁺, Cd²⁺, Cu²⁺, Ni²⁺, Pb²⁺ and Zn²⁺) in aqueous solution by saponified and cross-linked sugar-beet pulp was investigated. Saponification doubled the cation-exchange capacity, while cross-linking decreased specific surface area and hydration properties to low and stable values independent of pH and ionic strength conditions. The sorption isotherms indicated a high metal-binding capacity which increased with sorbent concentration, and followed a clear order of selectivity: Cu²⁺˜Pb²⁺ Zn²⁺˜Cd²⁺ > Ni²⁺ > Ca²⁺. The sorption data were better represented by the Langmuir isotherm than by the Freundlich one, suggesting that the monolayer sorption, mainly due to ion-exchange, would not be disturbed by lateral interactions between cations sorbed with similar sorption energies. The same order of selectivity could be drawn from the Langmuir parameters, sorption equilibrium constants (K_L) and maximum binding capacities (Me_Amax). Whatever the cation, K_L decreased with increasing sorbent concentration, while Me_bmax increased. Higher quantities of Cu²⁺ and Pb²⁺ than predicted by the one divalent cation to two carboxyl functions ratio were bound. This was attributed to the partial contribution to the sorption phenomenon of hydroxyl functions close to ionic sites, explaining the higher affinity of such cations for substrates. Cross-linked pulp exhibited higher metalbinding capacity per volume unit than the raw pulp.     

Real-Time State Estimation in a Flight Simulator Using fNIRS

Working memory is a key executive function for flying an aircraft. This function is particularly critical when pilots have to recall series of air traffic control instructions. However, working memory limitations may jeopardize flight safety. Since the functional near-infrared spectroscopy (fNIRS) method seems promising for assessing working memory load, our objective is to implement an on-line fNIRS-based inference system that integrates two complementary estimators. The first estimator is a real-time state estimation MACD-based algorithm dedicated to identifying the pilot’s instantaneous mental state (not-on-task vs. on-task). It does not require a calibration process to perform its estimation. The second estimator is an on-line SVM-based classifier that is able to discriminate task difficulty (low working memory load vs. high working memory load). These two estimators were tested with 19 pilots who were placed in a realistic flight simulator and were asked to recall air traffic control instructions. We found that the estimated pilot’s mental state matched significantly better than chance with the pilot’s real state (62% global accuracy, 58% specificity, and 72% sensitivity). The second estimator, dedicated to assessing single trial working memory loads, led to 80% classification accuracy, 72% specificity, and 89% sensitivity. These two estimators establish reusable blocks for further fNIRS-based passive brain computer interface development.