Cellulase EGZ of Erwinia chrysanthemi: structural organization and importance of His98 and Glu133 residues for catalysis

Biochemical, genetic and primary sequence analyses of the Erwiniachrysanthemi endoglucanase EGZ allowed us to identify two functionaldomains and to locate their boundaries. The catalytic domainextends from residue 1 to 288, while a domain required for EGZto bind to microcrystalline cellulose lies from residues 324to 385. Each domain was found capable of functioning in theabsence of the other. A region rich in Pro, Thr and Ser residueslinks both domains and appeared to be susceptible to proteolyticattack. Based upon predictions derived from a method developedto compare sequences sharing a low level of similarity, e.g.hydrophobic cluster analysis (HCA), we analysed the importanceof either residue His98 or Glul33 in EGZ catalytic activity.Two EGZ-derived proteins were engineered in which either His98or Glul33 amino acid was converted to an Ala residue. Characterizationof the purified proteins showed that no enzymatic activity couldbe detected, by using carboxymethylcellulose (CMC) or paranitrophenyl-cellobioside(pNPC) as substrates, while both mutated proteins retained thecapacity to bind to microcrystalline cellulose. These studies,which to date constitute the first experimental testing of HCA-derivedpredictions, allowed us to identify two particular amino acidsinvolved in cellulolytic activity. By taking into account datafrom chemical modification studies of other cellulases, we speculatethat the His98 residue is involved in the folding of the catalyticdomain while the Glul33 residue intervenes directly in the ß,1–4 glycosidic bond cleavage.     

Etude de la reduction sur electrode de mercure de thioethers et de sulfoniums derives de l'acide β-mercaptopyruvique

Thioethers with general formula RSCH₂COCOOR′ where R is paratolyl, methyl or ethyl, and sulfonium salts like Br^?,(CH₃)₂$\text{S}\text{+}$-CH₂COCOOR′ which proceed from β-mercaptopyruvic acid or its ethylester, have been investigated polarographically and by means of controlled potential electrolysis, in aqueous or aquo—alcoholic media.Reduction of sulfonium salts at the mercury electrode is in accordance with the general rule a reductive cleavage of the substituting group RS— occurs. Behaviour of thioethers is not uniform. When R is aryl, cleavage of the carbone—sulphur bond still occurs; when R is alkyl, the carbonyl group undergoes the reduction and the substituted secondary alcohol is formed.     

Oxydation électrochimique de l'acétylène en solution aqueuse a des électrodes d'or

The electro-oxidation of aqueous solutions of acetylene at gold electrodes is studied by voltammetry and controlled potential electrolysis. A mechanism involving the oxidation of the gold electrode is presented for the electro-oxidation of acetylene at gold electrodes.     

The effect of orientation on the morphology and kinetics of solvent crazing in polystyrene

Unoriented, uniaxially oriented, and biaxially oriented polystyrene films were crazed by immersing samples in liquid n-hexane at 45°C. The craze morphology and crazing kinetics were studied as a function of the preorientation and thermal histories of the polymer films. The shape of the micropores was related to the degree of orientation of the film. Ellipsoidal microvoids were formed on the surfaces of uniaxially oriented films containing a residual glassy core. Unoriented samples displayed spherical microvoids 0.1 to 3 μ in diameter. The major-to-minor axis ratio of the micropores increased monotonically from 1/1 to 10/1 as the sample orientation was increased from 0% to 200%. The kinetics of the crazing process similarly increased with uniaxial orientation. Surfaces of unannealed films which crazed mainly during the sorption of liquid n-hexane displayed numerous micropores when examined by the SEM. Conversely, films which were extensively annealed crazed mainly during desorption regardless of subsequent orientation. These extensively annealed films exhibited surfaces with many fine cracks and few, if any, micropores.     

Vapor sorption and liquid interactions with glassy polyblends of polystyrene and poly(2,6-dimethyl-1,4-phenylene oxide)

Polystyrene, poly(phenylene oxide), and solution-cast blends of the parent homopolymers were exposed to normal hexane in the liquid and vapor phase. The kinetics of absorption and desorption, the sorption equilibria, and the kinetics of morphological changes were studied as a function of temperature and blend composition. Absorption kinetics of n-hexane vapor in all blends were largely controlled by polymer relaxations. The sorption rates from the vapor phase varied monotonically with blend composition and increased over a range of four orders of magnitude with increasing poly(phenylene oxide) content. The equilibrium n-hexane content similarly increased monotonically with poly(phenylene oxide) content although the increase was only by a factor of two over the entire range of compositions. These results were interpreted in light of and were completely consistent with earlier findings with pure polystyrene homopolymer. Films immersed in liquid n-hexane produced a white, opaque outer shell surrounding an essentially unaffected central core. The kinetics of this whitening process were much more rapid for each of the homopolymers than the kinetics characterizing morphological changes in the blends. These data suggest that film whitening is caused by crazing in the polystyrene-rich samples and that solvent-induced crystallization is involved in the whitening of the poly (phenylene oxide) rich material.     

Back pain and its correlates among workers in family care

This study is based on the empirical fact that among nurses large variations occur not only in clinical competency but also in individual productivity. The article proposes that competency-based targeted staff development programs can improve productivity as well as nursing performance. Research presented here shows that the nurses on units using targeted staff development increased the time spent on professional and direct care and reduced nonprofessional and indirect care tasks in comparison to nurses on the control nursing unit.     

Grain Refinement of TRIP‐Assisted Multiphase Steels through Strain‐Induced Phase Transformation

To develop high performance steels for automotive applications, enhanced strengthening mechanisms are required. This study aims at assessing the critical parameters leading to the refinement of the strain‐induced ferrite matrix of thermomechanically processed multiphase steels. Hot rolling simulations allowed the definition of the temperature, strain and cooling rate conditions bringing about the formation of strain‐induced ferrite with a reduced grain size. The relationship between the deformation and the concurrent or subsequent phase transformations is highlighted thanks to a thorough characterisation of the generated microstructures. It is also shown that the prior austenite grain size influences the distribution of the second phases within the finely grained ferrite matrix.     

Crystallographic features of theγ-to-α transformation in a Nb-added transformation-induced plasticity steel

A Nb-bearing transformation-induced plasticity (TRIP) steel was control rolled and a certain amount of austenite was retained through appropriate heat treatment. Electron backscatter diffraction (EBSD) measurements were conducted on specimens deformed to various reductions, and the orientations of theα grains formed within individual prior-austenite grains were compared to those expected from the common correspondence relationships. While most of the bainite orientations cluster around the Bain circles formed by these relations, the polygonal (allotriomorphic) ferrite formed at the austenite grain boundaries does not obey any of these relations with respect to the neighboring austenite orientations. Grain-scale variant selection was observed in both the deformed and undeformed austenite grains. The crystallographic features of the deformation-induced ferrite transformation are also discussed.     

La conservation apprise par observation: Variations sur quelques paramètres de la démonstration du modèle.

Studied the effectiveness of imitation and comprehension processes in learning conservation by observation: specifically, the extent to which some of the verbal and social characteristics of a model's correct demonstration of conservation problems regulate the learning of the principle involved. Three experiments were conducted with 3 groups of Canadian kindergarten and 1st-grade schoolchildren, balanced by age and sex. The same male model participated in all 3 experiments; 2 female models were added in Exp III. Classical liquid conservation and/or quantification problems were solved by the model(s) in the Ss' presence. Results show that acquisition occurred by a series of cognitive processes in which the role of social pressure to conform to the model's behavior was one of the parameters evaluated. (English abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)