Inhibition by chelating agents of the formation of active extracellular proteinase by Pseudomonas fluorescens 32A

The effect of chelating agents on extracellular proteinase production by Pseudomonas fluorescens 32A was examined. Increasing concentrations of orthophosphate slightly stimulated growth while inhibiting proteinase synthesis. Fifty per cent inhibition was found at 35 and 28 mM-orthophosphate at 5 and 20 degrees C respectively. Extracellular protein concentration was reduced by 30% when cells were grown with 100 mM-orthophosphate. Polyacrylamide gel electrophoresis of the cell-free supernatants suggested that reduced enzyme synthesis had taken place as evidenced by the decrease in staining intensity of the protein band corresponding to the proteinase. Other phosphate compounds could replace orthophosphate as an inhibitor. Extent of inhibition was related to chain length; polyphosphates with 4-6 or 13-18 phosphorus atoms were the most effective inhibitors. EDTA (0.5 mM) completely inhibited proteinase synthesis. This inhibition could be partly reversed by Ca2+ and, to a lesser extent, Mn2+. Proteinase production at 5 degrees C in skim milk was completely inhibited by phosphate glass (P13-P18). Control experiments showed that loss of activity with chelators was not due to inhibition of preformed enzyme. The results suggest a possible role for polyphosphates in controlling proteinase production in stored milk.     

The multi-structure of oxidized-reduced tungsten carbide surface(s)

The XPS of bulk tungsten carbide, partially oxidized WC surfaces at 373 and 573 K as well as tungsten trioxide have been reported. Bulk WC has been prepared from WO₃ as a starting material in a mixture of CH₄ (20%) and H₂ (80%) at 1150 K for 4 h, while partially oxidized WC surfaces were prepared by oxygen chemisorption on a clean WC surface at 200 K, then the temperatures were raised to 373 and 573 K respectively. The XPS of a freshly prepared WC reveals the presence of a small amount of WO₃ on the surface and a slightly higher concentration in the bulk. The oxygen-exposed fresh WC surfaces and surfaces treated at temperatures higher than 373 K show the presence of WO₃ in a considerable quantity depending on the length and the treatment temperature. Ar⁺ bombardment of this partially oxidized surface reduces WO₃ to WO₂ and W(0), while WC is partially reduced to W(0). Isomerization reactions of alkanes on oxygen-exposed WC surface occurs in reality on a composite surface structure containing WC, WO₃, WO₂ and elemental W(0).     

Effect of various parameters on the level of mixing in continuous flow systems

Variations of the level of mixing in a flow system have been investigated as a function of the following parameters: diameter, shape and speed of the agitator, feed rate and position of the feed inlet. At agitator speeds inferior to a critical value, a minimum level of mixing is observed which depends on the position of the feed inlet. At speeds superior to the critical value, the level of mixing increases linearly with agitator speed, at a given feed rate, until conditions of perfect mixing are reached. The critical agitator speed and the position of each straight line depend on the agitator size. A modified Reynolds number makes possible a more general correlation. At a given agitator speed, superior to the critical value, the level of mixing decreases as the feed rate increases, due to the smaller amount of energy imparted by the agitator per unit mass of feed. The effect of agitator shape on the level of mixing is rather pronounced as it affects the flow patterns inside the reservoir.     

The substrate specificity of a recombinant cysteine protease from Leishmania mexicana: application of a combinatorial peptide library approach

The substrate specificity of CPB2.8DeltaCTE, a recombinant cysteine protease from Leishmania mexicana, was mapped by screening a fluorescence-quenched combinatorial peptide library. Results from library screening indicated a preference for Arg or Lys in the S(3) subsite and for hydrophobic residues, both aliphatic and aromatic, in S(2). The S(1) subsite exhibited a specificity for the basic residues Arg and Lys. Generally, the specificity of the primed subsites was less strict compared with the non-primed side which showed preference for Arg, Lys and Ala in S'(1), Arg, Pro and Gly in S'(2) and Lys, Arg and Ser in S'(4). By contrast, a strict preference for the basic residues Arg and Lys was found for S'(3). Overall, there was a trend for basic residues in alternating subsites and smaller residues in the primed sites compared with the non-primed sites. In addition, there were strict requirements for the amino acids in subsites S(3)--S(1). Fluorescence-quenched peptides from the library with the highest on-resin cleavage were resynthesised and their kinetics of hydrolysis by CPB2.8DeltaCTE assessed in solution phase assays. Several good substrates containing the quintessential dipeptide particular to cathepsin-L-like enzymes, -F-R/K-, in P(2) and P(1) were identified (e.g. Y(NO(2))-EKFR down arrow RGK-K(Abz)G, Abz=2-aminobenzoyl; k(cat)K(m)(-1)=4298 mM(-1)s(-1)). However, novel substrates containing the dipeptide -L/I-Q- in P(2) and P(1) were also well hydrolysed (e.g. Y(NO(2))-YLQ down arrow GIQK-K(Abz)G; k(cat)K(m)(-1)=2583 mM(-1)s(-1)). The effect of utilising different fluorescent donor--quencher pairs on the value of k(cat)K(m)(-1) was examined. Generally, the use of the Abz/Q-EDDnp donor--quencher pair (EDDnp=N-(2,4-dinitrophenyl)ethylenediamine) instead of K(Abz)/Y(NO(2)) resulted in higher k(cat)K(m)(-1) values for analogous substrates.     

Comparaison du modèle des réservoirs imparfaitement agités en série avec le modèle de dispersion axiale

The transfer function of the model of imperfectly mixed tanks in series, involving the three parameters p, m and n, is presented. It is thus possible to evaluate easily the residence time distribution curve E(θ) and the output response for a given input. This model is compared to the axial dispersion model, through the variance of the curve for E(θ) and the average absolute error between theoretical values and experimental data. A graphical representation relates the Péclet number of the axial dispersion model to the parameters of the p, m, n model and also to the variance of the curve for E(θ). The p, m, n model gives a good approximation of experimental data; it is shown to be more versatile than the axial dispersion model.     

Microstructured air-silica fibres: Recent developments in modelling, manufacturing and experiment

The main modelling methods devoted to microstructured air-silica optical fibres (MOFS) are presented and discussed. Then, the specific propagation properties ofMOFS are studied in detail. Characteristics measured on fibres manufactured in our laboratory or reported in the literature are analysed. A large number of potential and demonstrated applications are presented and the obtained performances are discussed. A particular attention is given to hollow-core photonic bandgap fibres and their applications.     

DAILY AVERAGED 2D WATER TEMPERATURE MODEL FOR THE ST. LAWRENCE RIVER

A daily averaged two‐dimensional water temperature model has been developed for the freshwater part of the St. Lawrence River, between Lake St. Louis and Trois‐Rivières (Québec, Canada). The model was first calibrated and validated for the area of Lake St. Pierre, a natural enlargement of the river subject to strong lateral and longitudinal thermal variations. Forecasts from the Global Environmental Multiscale model were used in preference to observations from meteorological stations for model inputs, both to increase the spatial resolution and ultimately to allow the water temperature model to be used in predictive mode. The resulting model provided daily water temperature estimates with an overall root mean square error (RMSE) of 1.18 °C and a Nash–Sutcliffe coefficient of 0.44. Comparisons between Landsat images and simulations demonstrated that the model not only simulated accurate water temperature values but also showed the adequacy of the model in general. It not only simulated local water temperature relatively accurately but also provided a good representation of the spatial water temperature patterns within the study area. The error varied between deep and shallow water areas. In deeper water, the overall RMSE is 0.41 °C, and the modified Nash coefficient rises up to 0.92. Because shallow water areas are subject to greater variations, longer, more spatially dense data sets will be needed to refine the hydrodynamic and thermal budget models for those specific areas. Copyright © 2013 John Wiley & Sons, Ltd.     

New optimization method is highly suitable for chemical engineering applications

A new optimization method involving only elementary calculus represents a significant simplification over existing methods. It makes for the easy and rapid solution of many complex problems in chemical engineering. In addition to making use of the first derivative, as in most other methods, the new method also calls for the second derivative of the function to be optimized. When going from one point to another, the method consists essentially in adding simultaneously to each independent variable an increment which, for a given variable, is equal to the negative ratio of the first partial derivative to the second partial derivative, and so on until optimum conditions are reached. A few mathematical examples illustrate the speed of the new method and permit comparisons with other well known methods. Numerical applications pertaining to chemical engineering are also presented.     

Study on a cobalt silica catalyst during reduction and Fischer–Tropsch reaction: In situ EXAFS compared to XPS and XRD

The reduction of a 25 wt% Co/SiO₂ catalyst for the hydrocarbon synthesis has been followed by several techniques: XRD, TPR, XPS and in situ EXAFS. Before reduction the cobalt is present as a Co₃O₄ spinel phase. A two-step reduction of Co₃O₄ to CoO and then to Co° is observed by EXAFS. This is consistent with XPS (surface) and TPR or XRD (bulk) studies. During CO/H₂ reaction, cobalt is always in the metallic state (EXAFS). The coordination number of cobalt has been determined at each reduction step and during CO hydrogenation reaction.