Browsing
     by title


0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

or enter first few letters:   
OK
Full Text
Peer Reviewed
See detailKinetic and crystallographic studies of extended-spectrum GES-11, GES-12, and GES-14 β-lactamases.
Delbrück, Heinrich; Bogaerts, Pierre; Kupper, Michaël et al

in Antimicrobial Agents and Chemotherapy (2012), 56(11)

GES-1 is a class A extended-spectrum β-lactamase conferring resistance to penicillins, narrow- and expanded-spectrum cephalosporins, and ceftazidime. However, GES-1 poorly hydrolyzes aztreonam and ... [more ▼]

GES-1 is a class A extended-spectrum β-lactamase conferring resistance to penicillins, narrow- and expanded-spectrum cephalosporins, and ceftazidime. However, GES-1 poorly hydrolyzes aztreonam and cephamycins and exhibits very low k(cat) values for carbapenems. Twenty-two GES variants have been discovered thus far, differing from each other by 1 to 3 amino acid substitutions that affect substrate specificity. GES-11 possesses a Gly243Ala substitution which seems to confer to this variant an increased activity against aztreonam and ceftazidime. GES-12 differs from GES-11 by a single Thr237Ala substitution, while GES-14 differs from GES-11 by the Gly170Ser mutation, which is known to confer increased carbapenemase activity. GES-11 and GES-12 were kinetically characterized and compared to GES-1 and GES-14. Purified GES-11 and GES-12 showed strong activities against most tested β-lactams, with the exception of temocillin, cefoxitin, and carbapenems. Both variants showed a significantly increased rate of hydrolysis of cefotaxime, ceftazidime, and aztreonam. On the other hand, GES-11 and GES-12 (and GES-14) variants all containing Ala243 exhibited increased susceptibility to classical inhibitors. The crystallographic structures of the GES-11 and GES-14 β-lactamases were solved. The overall structures of GES-11 and GES-14 are similar to that of GES-1. The Gly243Ala substitution caused only subtle local rearrangements, notably in the typical carbapenemase disulfide bond. The active sites of GES-14 and GES-11 are very similar, with the Gly170Ser substitution leading only to the formation of additional hydrogen bonds of the Ser residue with hydrolytic water and the Glu166 residue. [less ▲]

Detailed reference viewed: 15 (2 ULg)
Full Text
Peer Reviewed
See detailKinetic and structural optimization to catalysis at low temperatures in a psychrophilic cellulase from the Antarctic bacterium Pseudoalteromonas haloplanktis
Garsoux, G.; Lamotte, J.; Gerday, Charles ULg et al

in Biochemical Journal (2004), 384(Pt 2), 247-253

The cold-adapted cellulase CelG has been purified from the culture supernatant of the Antarctic bacterium Pseudoalteromonas haloplanktis and the gene coding for this enzyme has been cloned, sequenced and ... [more ▼]

The cold-adapted cellulase CelG has been purified from the culture supernatant of the Antarctic bacterium Pseudoalteromonas haloplanktis and the gene coding for this enzyme has been cloned, sequenced and expressed in Escherichia coli. This cellulase is composed of three structurally and functionally distinct regions: an N-terminal catalytic domain belonging to glycosidase family 5 and a C-terminal cellulose-binding domain belonging to carbohydrate-binding module family 5. The linker of 107 residues connecting both domains is one of the longest found in cellulases, and optimizes substrate accessibility to the catalytic domain by drastically increasing the Surface of cellulose available to a bound enzyme molecule. The psychrophilic enzyme is closely related to the cellulase Cel5 from Erwinia chrysanthemi. Both k(cat) and k(cat)/K-m values at 4 degreesC for the psychrophilic cellulase are similar to the values for Cel5 at 30-35 degreesC, suggesting temperature adaptation of the kinetic parameters. The thermodynamic parameters of activation of CelG suggest a heat-labile, relatively disordered active site with low substrate affinity, in agreement with the experimental data. The structure of CelG has been constructed by homology modelling with a molecule of cellotetraose docked into the active site. No structural alteration related to cold-activity can be found in the catalytic cleft, whereas several structural factors in the overall structure can explain the weak thermal stability, suggesting that the loss of stability provides the required active-site mobility at low temperatures. [less ▲]

Detailed reference viewed: 12 (0 ULg)
Full Text
Peer Reviewed
See detailKinetic characterization of the monofunctional glycosyltransferase from Staphylococcus aureus
Terrak, Mohammed ULg; Nguyen-Disteche, M.

in Journal of Bacteriology (2006), 188(7), 2528-2532

The glycosyltransferase (GT) module of class A penicillin-binding proteins (PBPs) and monofunctional GTs (MGTs) belong to the GT51 family in the sequence-based classification of GTs. They both possess ... [more ▼]

The glycosyltransferase (GT) module of class A penicillin-binding proteins (PBPs) and monofunctional GTs (MGTs) belong to the GT51 family in the sequence-based classification of GTs. They both possess five conserved motifs and use lipid II precursor (undecaprenyl-pyrophosphate-N-acetylglucosaminyl-N-acetylmuramoyl- pentapeptide) to synthesize the glycan chain of the bacterial wall peptidoglycan. MGTs appear to be dispensable for growth of some bacteria in vitro. However, new evidence shows that they may be essential for the infection process and development of pathogenic bacteria in their hosts. Only a small number of class A PBPs have been characterized so far, and no kinetic data are available on MGTs. In this study, we present the principal enzymatic properties of the Staphylococcus aureus MGT. The enzyme catalyzes glycan chain polymerization with an efficiency of similar to 5,800 M-1 s(-1) and has a pH optimum of 7.5, and its activity requires metal ions with a maximum observed in the presence of Mn2+. The properties of S. aureus MGT are distinct from those of S. aureus PBP2 and Escherichia coli MGT, but they are similar to those of E. coli PBP1b. We examined the role of the conserved Glu100 of S. aureus MGT (equivalent to the proposed catalytic Glu233 of E. coli PBP1b) by site-directed mutagenesis. The Glu100Gln mutation results in a drastic loss of GT activity. This shows that Glu100 is also critical for catalysis in S. aureus MGT and confirms that the conserved glutamate of the first motif EDXXFXX(H/N)X(G/A) is likely the key catalytic residue in the GT51 active site. [less ▲]

Detailed reference viewed: 23 (2 ULg)
Full Text
Peer Reviewed
See detailKinetic Energy Release Distributions for Tropylium and Benzylium Ion Formation from the Toluene Cation.
Fati, D.; Lorquet, Andrée ULg; Locht, Robert ULg et al

in Journal of Physical Chemistry A (2004), 108

Hydrogen loss from the toluene molecular ion generates benzylium (Bz(+)) and tropylium (Tr+) ions via two competitive and independent pathways. The corresponding kinetic energy release distributions ... [more ▼]

Hydrogen loss from the toluene molecular ion generates benzylium (Bz(+)) and tropylium (Tr+) ions via two competitive and independent pathways. The corresponding kinetic energy release distributions (KERDs) have been determined under various conditions in the metastable time window for toluene and perdeuterated toluene and have been analyzed by the maximum entropy method (MEM). The isomeric fraction Tr+/Bz(+) is found to be equal to 0.9 +/- 0.3, in good agreement with the values obtained using photodissociation and charge exchange experiments. It is, however, in disagreement with the value 5 +/- 2 deduced by Moon, Choe, and Kim (J. Phys. Cheln. A 2000, 104, 458) from KERD measurements. The origin of the discrepancy is suggested to be the inadequacy of the orbiting transition state theory (OTST) for the calculation of KERDs in hydrogen loss reactions. For both channels, more translational energy is released in the reaction coordinate than would be expected on statistical grounds because of the presence of a barrier along the reaction path. For the Bz(+) channel, the barrier entirely results from centrifugal effects. Rotational energy is converted into translation as a result of angular momentum conservation. Deuteration is observed to reduce the importance of the rotational energy flow in the reaction coordinate. The Tr+ channel is characterized by the presence of a reverse activation energy barrier of electronic origin. The energy in excess of the dissociation asymptote can be partitioned into two components: the reverse barrier plus a nonfixed energy contribution. About 40% of the reverse barrier is converted into relative translational motion of the fragments. Here again, a lower fraction of the nonfixed energy flows into translation for the deuterated isotopomer. [less ▲]

Detailed reference viewed: 96 (5 ULg)
Full Text
Peer Reviewed
See detailKinetic Energy Release Distributions in the Dissociation of Energy-Selected Fluoroethene and 1,1-Difluoroethene Ions.
Güthe, F.; Locht, Robert ULg; Leyh, Bernard ULg et al

in Journal of Physical Chemistry A (1999), 103

The unimolecular dissociation of energy-selected fluoroethene and 1,1-difluoroethene ions has been investigated by threshold photoelectron photoion coincidence TPEPICO) technique. The breakdown diagrams ... [more ▼]

The unimolecular dissociation of energy-selected fluoroethene and 1,1-difluoroethene ions has been investigated by threshold photoelectron photoion coincidence TPEPICO) technique. The breakdown diagrams of the 1,1-difluorethene and fluoroethene have been recorded between 13-22 eV. From time-of-flight (TOF) spectra, complete distributions of the kinetic energy released (KERD) in the dissociation of these energy-selected ions have been derived. For the HF-loss reaction channel, the KERD peaks at about 200 meV for low excitation energies but becomes thermal at higher excitation energies. For the F-loss channel, the KERD peaks at zero kinetic energy for low excitation energies but at about 200 meV for high excitation energy. The analysis of the KERD provides evidence that consecutive fragmentation takes place for the 1,1-difluoroethene at energies above 19 eV. [less ▲]

Detailed reference viewed: 32 (2 ULg)
Peer Reviewed
See detailThe kinetic growth anisotropy of the 123-(RE)BaCuO compounds
Vandewalle, Nicolas ULg; Ausloos, Marcel ULg

in Philosophical Magazine A (1995), 72(3), 727-736

The kinetic growth anisotropy of the melt-textured 123-(RE)BaCuO compounds, especially along the CuCO2 planes, is discussed here in detail. A computer model which simulates the grain growth of 123 ... [more ▼]

The kinetic growth anisotropy of the melt-textured 123-(RE)BaCuO compounds, especially along the CuCO2 planes, is discussed here in detail. A computer model which simulates the grain growth of 123 materials in the ab plane is presented. This kinetic growth model takes some bond anisotropy along the [100] and [110] directions into account. The model presented herein belongs to a hierarchical set of generalized Eden models as discussed in the Appendix. For different bond anisotropy parameters, the simulated 123-(RE)BaCUO grains exhibit square and octogonal overall shape which have been both optically observed. From simple kinetic arguments, we show that the 'faceting' of the 123-(RE)BaCuO grains finds its origin in a bond anisotropy rather than in a growth-rate anisotropy along some crystallographic directions. This is of general interest and opens new perspectives for developing the Eden model in the crystal-growth field. [less ▲]

Detailed reference viewed: 31 (0 ULg)
Full Text
Peer Reviewed
See detailKinetic mechanism of mitochondria carriers catalysing exchange reactions
Sluse, Francis ULg; Evens, A.; Duyckaerts, Claire ULg et al

in Journal of Biosciences (1990), 15

Detailed reference viewed: 7 (4 ULg)
Full Text
See detailKinetic mechanism of the adenylic and the oxoglutaruc carriers : a comparison
Sluse, Francis ULg; Sluse-goffart, C.; Duyckaerts, Claire ULg

in Azzi, A.; Nalecz, M. J.; Wojtczak, L. (Eds.) Anion carriers of mitochondrial membranes (1989)

Detailed reference viewed: 10 (1 ULg)
Full Text
Peer Reviewed
See detailKinetic mechanism of the exchanges catalysed by the adenine-nucleotide carrier.
Duyckaerts, Claire ULg; Sluse-Goffart, Claudine; Fux, Jean-pierre et al

in European Journal of Biochemistry (1980), 106

Detailed reference viewed: 14 (1 ULg)
Peer Reviewed
See detailA kinetic model of the formation of the hot oxygen geocorona. 1: Quiet geomagnetic conditions
Shematovich, V. I.; Bisikalo, D. V.; Gérard, Jean-Claude ULg

in Journal of Geophysical Research (1994), 99

A model of the hot oxygen geocorona in the transition region near the exobase is described. It is based on a Monte Carlo solution of the nonlinear Boltzmann equation for hot oxygen atoms produced by ... [more ▼]

A model of the hot oxygen geocorona in the transition region near the exobase is described. It is based on a Monte Carlo solution of the nonlinear Boltzmann equation for hot oxygen atoms produced by chemical processes usually considered as a source of hot oxygen (photodissociation of O2 and dissociative recombination of O2(+) and NO(+) ions). The evolution of the system is described stochastically as a series of random Markovian processes. The energy distribution function of the thermal and non-thermal O(3P) atoms and of the nonthermal O(1D) atoms is calculated from the thermospheric collision-dominated region to the exosphere where the gas flow is virtually collisionless. The model is applied to equatorial latitudes for conditions of low solar and geomagnetic activity. Numerical simulations show that the distribution function of thermal oxygen is increasingly perturbed by collisions with the hot oxygen population at high altitudes and departs significantly from a Maxwellian distribution at all altitudues. The number density and temperature of the nonthermal oxygen atoms are derived from their microscopic distribution function and found tobe in qualitative agreement with previous theoretical and experimental estimates. [less ▲]

Detailed reference viewed: 11 (0 ULg)
Peer Reviewed
See detailA kinetic model of the formation of the hot oxygen geocorona. 2: Influence of O(+) ion precipitation
Bisikalo, D. V.; Shematovich, V. I.; Gérard, Jean-Claude ULg

in Journal of Geophysical Research (1995), 100

A model for the oxygen geocorona near the exobase solving the nonlinear Boltzmann equation with a Monte Carlo method is used to calculate the distribution of the hot oxygen atoms during geomagnetically ... [more ▼]

A model for the oxygen geocorona near the exobase solving the nonlinear Boltzmann equation with a Monte Carlo method is used to calculate the distribution of the hot oxygen atoms during geomagnetically disturbed nighttime conditions. The precipitation of energetic O(+) ions and the subsequent enhancement of the hot O corona at high latitudes is simulated for the September 17, 1971, storm conditions. It is found that in such circumstances, the O(+) precipitation is a significant source of superthermal O atoms leading to important perturbations of the velocity distribution of the bulk oxygen population. The effective gas temperature near the exobase is similar to that in the undisturbed atmosphere, but the hot O density rises considerably over the quiet condition values. [less ▲]

Detailed reference viewed: 3 (0 ULg)
Full Text
Peer Reviewed
See detailKinetic of the hydrolysis of pectin galacturonic acid chains and quantification by ionic chromatography
Garna, H.; Mabon, N.; Nott, Katherine ULg et al

in Food Chemistry (2006), 96(3), 477-484

These experiments were designed to develop a rapid, repeatable and accurate analysis method for the quantification of galacturonic acid of pectins. Different pectin hydrolysis procedures (chemical and ... [more ▼]

These experiments were designed to develop a rapid, repeatable and accurate analysis method for the quantification of galacturonic acid of pectins. Different pectin hydrolysis procedures (chemical and enzymatic) were carried out with H2SO4, TFA and HCl at different acid concentrations (0.2, 1 and 2 M) and temperatures (80 and 100 degrees C). Enzymatic and combined chemical and enzymatic hydrolysis of pectin were also studied. A acid hydrolysis under drastic conditions (100 degrees C) is insufficient for complete hydrolysis and results in low recovery of galacturonic acid residues. Mild chemical hydrolysis (0.2, 1 and 2 M H2SO4 72 h at 80 degrees C) is also insufficient for complete depolymerization. Its main advantage is cleavage of the galacturonic acid chains into oligomeric forms without any degradation within 72 h of hydrolysis. However, enzymatic hydrolysis with VL9 for 2 h at 50 degrees C and combined chemical and enzymatic hydrolysis (0.2 M TFA at 80 degrees C for 72 h and VL9) give high recovery of this acid. Analysis of the liberated sugar residue by HPAEC allows us to determine the galacturonic acid composition of this polysaccharide accurately with high selectivity and sensitivity in one assay without the need for derivatization. (c) 2005 Elsevier Ltd. All rights reserved. [less ▲]

Detailed reference viewed: 172 (4 ULg)
Full Text
Peer Reviewed
See detailKinetic properties of the alpha(2) homo-oligomeric glycine receptor impairs a proper synaptic functioning
Mangin, J. A.; Baloul, M.; de Carvalho, L. P. et al

in Journal of Physiology-London (2003), 553(2), 369-386

Ionotropic glycine receptors (GlyRs) are present in the central nervous system well before the establishment of synaptic contacts. Immature nerve cells are known, at least in the spinal cord, to express ... [more ▼]

Ionotropic glycine receptors (GlyRs) are present in the central nervous system well before the establishment of synaptic contacts. Immature nerve cells are known, at least in the spinal cord, to express alpha(2) homomeric GlyRs, the properties of which are relatively unknown compared to those of the adult synaptic form of the GlyR (mainly alpha(1)/beta heteromeres). Here, the kinetics properties of GlyRs at the single-channel level have been recorded in real-time by means of the patch-clamp technique in the outside-out configuration coupled with an ultra-fast flow application system (< 100 µs). Recordings were performed on chinese hamster ovary (CHO) cells stably transfected with the a, GlyR subunit. We show that the onset, the relaxation and the desensitisation of α(2) homomeric GlyR-mediated currents are slower by one or two orders of magnitude compared to synaptic mature GlyRs and to other ligand-gated ionotropic channels involved in fast synaptic transmission. First latency analysis performed on single GlyR channels revealed that their slow activation time course was due to delayed openings. When synaptic release of glycine was mimicked (1 mM glycine; 1 ms pulse duration), the opening probability of α(2) homomeric GlyRs was low (P-o ≈ 0.1) when compared to mature synaptic GlyRs (P-o = 0.9). This low P-o is likely to be a direct consequence of the relatively slow activation kinetics of α(2) homomeric GlyRs when compared to the activation kinetics of mature α(1)/β GlyRs. Such slow kinetics suggest that embryonic α(2) homomeric GlyRs cannot be activated by fast neurotransmitter release at mature synapses but rather could be suited for a non-synaptic paracrine-like release of agonist, which is known to occur in the embryo. [less ▲]

Detailed reference viewed: 14 (0 ULg)
Peer Reviewed
See detailKinetic properties of the Bacillus licheniformis Penicillin-binding proteins
Lepage, Sophie; Galleni, Moreno ULg; Lakaye, Bernard ULg et al

in Biochemical Journal (1995), 309

Detailed reference viewed: 12 (2 ULg)
Full Text
Peer Reviewed
See detailThe kinetic properties of the carboxy terminal domain of the Bacillus licheniformis 749/I BlaR penicillin-receptor shed a new light on the derepression of beta-lactamase synthesis
Duval, Valérie; Swinnen, Marc; Lepage, Sophie et al

in Molecular Microbiology (2003), 48(6), 1553-1564

To study the properties of the BlaR penicillin-receptor involved in the induction of the Bacillus licheniformis beta-lactamase, the water-soluble carboxy terminal domain of the protein (BlaR-CTD) was ... [more ▼]

To study the properties of the BlaR penicillin-receptor involved in the induction of the Bacillus licheniformis beta-lactamase, the water-soluble carboxy terminal domain of the protein (BlaR-CTD) was overproduced in the periplasm of Escherichia coli JM105 and purified to protein homogeneity. Its interactions with various beta-lactam antibiotics were studied. The second-order acylation rate constants k(2)/K' ranged from 0.0017 to more than 1 muM(-1) s(-1) and the deacylation rate constants were lower than 4x10(-5) s(-1) . These values imply a rapid to very rapid formation of a stable acylated adduct. BlaR-CTD is thus one of the most sensitive penicillin-binding proteins presently described. In the light of these results, the kinetics of beta-lactamase induction in Bacillus licheniformis were re-examined. When starting with a rather high cell density, a good beta-lactamase substrate such as benzylpenicillin is too sensitive to beta-lactamase-mediated hydrolysis to allow full induction. By contrast, a poor beta-lactamase substrate (7-aminocephalosporanic acid) can fully derepress beta-lactamase expression under conditions where interference of the antibiotic with cell growth is observed. These results suggest that acylation of the penicillin receptor is a necessary, but not sufficient, condition for full induction. [less ▲]

Detailed reference viewed: 49 (13 ULg)
Peer Reviewed
See detailKinetic study of 1,2-dichloroethane hydrodechlorination with a Pd-Ag/SiO2 sol-gel catalyst
Heinrichs, Benoît ULg; Delhez, P.; Schoebrechts, Jean-Paul et al

in 1st European Congress on Chemical Engineering, ECCE1 (Vol. 4, pp. 2919-2922) (1997, May 04)

Detailed reference viewed: 13 (2 ULg)