The indirect nature of interaction of glucose transport with the system transporting galactosides

The membrane transport systems for galactosides and glucose derivatives interact in enteric microorganisms. Stop-flow experiments with a double wavelength spectrophotometer and a flow-through cuvette (designed to minimize light-scattering effects) were used to measure the speed of interaction in Escherichia coli. The in vivo hydrolysis of ortho-nitrophenol-beta-D-galactopyranoside was measured by comparing the light transmitted by cell suspensions at 420 nm with that at 500 nm. Measurements at the latter wavelength corrected for residual scattering effects. The stop-flow experiment allowed the study of the early kinetics of transport and hydrolysis. It was found with strain ML308 that there was a significant lag in the achievement of steady-state inhibition by glucose and its derivative methyl-alpha-D-glucopyranoside (alpha MG). This strain constitutively produces high levels of permease and beta-galactosidase. The absorbancy increases at 420 nm are limited by transport because the beta-galactosidase is present inside the cells in excess. From earlier results, it was not surprising that inhibition is delayed with low concentrations of the glucose compounds, but the new double wavelength technique showed no kinetic component of rapid inhibition. This result therefore excludes competition for some membrane-bound component and is consistent with the production of the dephosphorylated form of the soluble Enzyme IIIglu that binds and inhibits the permease system in the membrane.     

Swine liver l-leucine aminopeptidase: improved purification procedure

An l-leucine aminopeptidase, having a specificity toward the substrate l-leucine amide, was purified 1084-fold from swine liver with a yield of 50.7 per cent. Purification procedure was carried out using successively centrifugation at 105 000 × g fractionation by ammonium sulfate, DEAE Sephacel chromatography and zonal ultracentrifugation.Enzyme homogeneity and purity studies were carried out by analytical ultracentrifugation and polyacrylamide gel electrophoresis.In SDS gel polyacrylamide a single band was observed. It corresponded to a 55 000 molecular weight protein.     

Modification of redox equilibria between heme and flavin within yeast flavocytochrome b2 (l-lactate cytochrome c reductase) upon binding of pyruvate,the reaction product

Direct determinations of the concentration of semiquinone spin in redox equilibrium with the cytochrome b₂ moiety were carried out at room temperature in the presence of added pyruvate or in its absence. Results show that redox potentials of the one-electron couples of the prosthetic flavin are markedly affected by binding of pyruvate the reaction product in the oxidation of l-lactate. The proportion of flavin semiquinone nearly reaches then 100 per cent.     

Le Mané Lud en sauvetage (Locmariaquer, Morbihan). Enregistrement et restitution de signes gravés dans une tombe à couloir néolithique

The great tumulus of the Mané Lud is more known for its passage grave in secondary addition that finishes the western extremity and that contains a number of carvings among the most famous of the European corpus. Ten steles will be here described and illustrated by photography and drawings whose realization will have demanded more 600 hours of work, undertaken on the terrain as well as in laboratory. Several signs are inescapable and validate by their discovery the simple method of acquisition and numerical image processing that we have developed these last years. The majority of carvings is equally better specified and allowed henceforth a re-interpretation of associations of signs united on a same support, but equally a simultaneous perusal of these steles understood as monuments fully fledged, functioning originally in a whole other special and historical context. The back stele, often considered as the master piece of the mortuary structure, and residing nevertheless one armorican engraving among the most badly interpreted and one of the most cryptic, appears as a representation in fact particularly succeeded of a spermwhale, staggering cetacean that our anterior studies had already sensed.     

Comparison of Bayesian-Utilitarian and Maximin Principle Approaches

The Precautionary Principle implies the adoption of a set of rules aimed at avoiding possible future harm associated with suspected, but not ascertained, risk factors. Several philosophical, economical and societal questions are implied by precaution-based public health decision making. The purpose of the present paper is to specify the scope of the principle examining the notion of uncertainty involved, and the implication of different approaches to the decision making process. The Bayesian-utilitarian approach and the approach based on the maximin principle will be considered, and the different meaning of prudence in the two settings will be discussed. In a Bayesian-utilitarian approach the small number of attributable cases will end up in a low average expected value, easily regarded as acceptable in a cost-benefit analysis. In a maximin approach, on the other hand, the issue will be to consider the high etiologic fraction of a rare disease in the highest category of exposure. In the light of the aforementioned cautions in interpretation, the core difference between the two approaches has to do with the choice between averaging knowledge or equitably distributing technological risks.     

Low community photosynthetic quotient in coral reef sediments

Fluxes of dissolved inorganic carbon and oxygen at the water-sediment interface were measured at eight coral reef stations (Indian Ocean) in summer and winter. The dark fluxes provided the community respiratory quotient (CRQ = dissolved inorganic carbon release / oxygen uptake) and the diurnal fluxes corrected from the dark fluxes gave the community photosynthetic quotient (CPQ = oxygen gross release / dissolved inorganic carbon gross uptake). The CRQ and the winter CPQ were not significantly different from 1. Summer CPQ (0.79; SD 0.02) was significantly lower than 1 due to the combined effect of the daily evolution of the community respiration and the discrepancy between the daily evolution in community oxygen respiration and community carbon respiration. These results highlight the importance of measuring simultaneously the benthic community production and respiration for long term integrated data sets, instead of the traditional daily or seasonal budget calculations from limited measures of community respiration. To cite this article: D. Taddei et al., C. R. Biologies 331 (2008).     

Contribution to the logistic theory of growth: temporal structure and growth potential

The analysis of a structured population according to three (juvenile, mature and senescent) cellular states is carried out within the framework of Delattre's transformation systems theory. Growth in number, with the dissymmetry of cell divisions, is determined by an autocatalysis process under the constraint of the availability of a source. Two models are presented: their dynamics results in a growth of the exponential type or of the sigmoidal type, respectively. In the sigmoidal case, the logistic equation (Richards-Nelder's function with adjunction of a lower asymptote Y not equal to 0) fits satisfactorily the simulated data of the total cell number Y. The growth potential is defined as the instantaneous capacity of autocatalysis, which is expressed in relation to the present 'mitotic resources' (source + non-senescing mature cells). The acceleration variations d2Y/dt2 are in close agreement with the growth potential gradient. The analysis is then generalized to other population structuring. As a result, the logistic equation can be interpreted in terms of a formal model of growth of a structured population submitted to autocatalysis and competition.     

Cytomechanics of cell deformations and migration: from models to experiments

A cytomechanical model bas been proposed to analyse cell-cell interactions and cell migration through chemotaxis. We consider as the leading assumption that the cell cortical tension is locally modified by the protrusive activity of neighbour cells and binding of chemoattractant molecules to membrane receptors respectively. The model derives from the one initially proposed by Alt and Tranquillo (1995), which successfully describes experimentally observed cyclic autonomous cell shape changes. It is based on force balance equations coupling intracellular hydrostatic pressure and cell cortex contraction. Considering the protrusive dynamics of L929 fibroblats observed by videomicroscopy, we simulated the influence of neighbouring protrusions on a cell spontaneous pulsating behaviour. We further investigated the role of an extracellular gradient as another kind of external stimulus. The model illustrates how binding of chemoattractant molecules can induce a cell morphological instability that, above an intracellular stress threshold, will break the cell-substratum attachment. As a result, realistic cell chemotaxis can be simulated.