Search results for "substrate"
showing 10 items of 1018 documents
Temperature effect on solubility of aroma compounds in various aqueous solutions
2005
International audience; Solubility of nine aroma compounds (methyl ketones, ethyl esters, aldehyde and alcohol) in various aqueous solutions was measured by the mutual solubility method from -10 to +10degreesC. Influence of both, the nature (carbohydrates and polyols) and the substrate concentration (from 0 to 57.5g/100g) on aroma solubility in aqueous solutions was studied. Aroma solubility in water decreased when aroma hydrophobicity increased. Aroma solubility in various aqueous solutions decreased when substrate concentration increased; their solubility was higher in polyols solutions than in polysaccharides ones. Temperature effect on aroma solubility showed a noncontinuous evolution f…
Use of artificial substrates for sampling benthic macroinvertebrates in the assessment of water quality of large lowland rivers
2004
The objective of this investigation was to evaluate the usefulness of the artificial substrate sampler in collecting macroinvertebrates for water quality assessment of Polish lowland rivers. This paper presents the results of a comparative study between two different sampling techniques, i.e. nettings filled with brick as artificial substrates and handnet sampling. The validity of applying the biotic index method is also demonstrated. The Belgian Biotic Index (BBI) method and the lower Nysa Kłodzka river were chosen for study. Macroinvertebrates were collected seasonally at five sampling sites. Although some invertebrate taxa revealed a specific preference for one of the two tested sampling…
Synergistic enhancement via plasmonic nanoplate-bacteria-nanorod supercrystals for highly efficient SERS sensing of food-borne bacteria
2017
Bio-sensing techniques utilizing metallic nanoparticles as a probe have gained more and more attention and play today an important role in the detection of bacteria. To date, although several sensing materials have been tested, there is still a long way to go to achieve a fast, low-cost, ultrasensitive and multifunctional substrate suitable for a universal biosensor for detection of bacterial cells. Here, we report a novel probe design based on anisotropic plasmonic nanoparticles organized to a biocompatible 3D bio-inorganic scaffold, i.e., nanoplate-bacteria-nanorod supercrystals (NBNS) with extremely high surface-enhanced Raman spectroscopic (SERS) activity as a model of synergistic plasm…
The catalytic mechanism of glyceraldehyde 3-phosphate dehydrogenase from Trypanosoma cruzi elucidated via the QM/MM approach
2013
Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has been identified as a key enzyme involved in glycolysis processes for energy production in the Trypanosoma cruzi parasite. This enzyme catalyses the oxidative phosphorylation of glyceraldehyde 3-phosphate (G3P) in the presence of inorganic phosphate (Pi) and nicotinamide adenosine dinucleotide (NAD+). The catalytic mechanism used by GAPDH has been intensively investigated. However, the individual roles of Pi and the C3 phosphate of G3P (Ps) sites, as well as some residues such as His194 in the catalytic mechanism, remain unclear. In this study, we have employed Molecular Dynamics (MD) simulations within hybrid quantum mechanical/molecular …
The L-tartrate/succinate antiporter TtdT (YgjE) of L-tartrate fermentation in Escherichia coli.
2007
ABSTRACT Escherichia coli ferments l -tartrate under anaerobic conditions in the presence of an additional electron donor to succinate. The carrier for l -tartrate uptake and succinate export and its relation to the general C 4 -dicarboxylate carriers DcuA, DcuB, and DcuC were studied. The secondary carrier TtdT, encoded by the ttdT (previously called ygjE ) gene, is required for the uptake of l -tartrate. The ttdT gene is located downstream of the ttdA and ttdB genes, encoding the l -tartrate dehydratase TtdAB. Analysis of mRNA by reverse transcription-PCR showed that ttdA , ttdB , and ttdT are cotranscribed. Deletion of ttdT abolished growth by l -tartrate and degradation of l -tartrate c…
Preorganization and reorganization as related factors in enzyme catalysis: the chorismate mutase case.
2003
In this paper a deeper insight into the chorismate-to prephenate-rearrangement, catalyzed by Bacillus subtilis chorismate mutase, is provided by means of a combination of statistical quantum mechanics/molecular mechanics simulation methods and hybrid potential energy surface exploration techniques. The main aim of this work is to present an estimation of the preorganization and reorganization terms of the enzyme catalytic rate enhancement. To analyze the first of these, we have studied different conformational equilibria of chorismate in aqueous solution and in the enzyme active site. Our conclusion is that chorismate mutase preferentially binds the reactive conformer of the substrate--that…
Propanediol-1,2-dehydratase and metabolism of glycerol of Lactobacillus brevis
1984
While most strains of heterofermentative lactobacilli and strains of Leuconostoc species contained only traces of a dehydratase reacting with glycerol or propanediol-1,2, three strains of Lactobacillus brevis and one strain of L. buchneri that metabolized glycerol readily in the presence of glucose, contained propanediol-1,2 dehydratase (EC 4.2.1.28). This cobamide requiring enzyme from L. brevis B 18 was partially purified. It reacts with the substrates propanediol-1,2, glycerol and ethanediol-1,2 with the relative activities of about 3:2:1. This ratio remained unchanged throughout the purification procedure. The substrate affinities were measured: propanediol-1,2 K m=0.6 mM, glycerol K m=…
Modeling for the active site nitrate reductase. Oxidation of the complex [MovO(O2CC(S) CH3Ph)2]− by nitrate and nitrite in methanol
1998
Abstract Under acid conditions the [MoVIO2(O2CC(S)CH1Ph)2]2 reacts with thiols to yield the monomeric [MoVO(O2CC(S)CH3Ph)2] and disulfide. The reduced complex [MoVO(O2CC(S)CH3Ph)2]− can react with NO3− and NO2− in a one-electron step yeilding respectively NO2 and NO and the original molybdenum (VI)-dioxo complex. The experimental pseudo-first-order rate constant with respect to the Mo(V) complex at 25°C was found to be kobs=2.3×10−4s−1 for NO3− and kobs=1.0×10−2 for NO2−. Oxo transfers to and from the substrate have been coupled to produce a catalytic system which turns over the reaction RSH+(No3− or NO2−)+H+a 1 2 [ RS ] 2 +( NO ] 2 or NO )+ H 2 O , in which thiols, NO1− and NO2− serve as a…
Kinetics of citrate uptake in growing cells ofLeuconostocspp.
1996
Citrate uptake was studied in growing cells of Leuconostoc mesenteroides subsp. mesenteroides. A Michaelis-Menten pattern with the dianionic form of citrate as the limiting substrate has been proposed. It was validated for different fermentations varying the initial citrate concentrations and the pH medium. This latter did not modify the rate of the process which was clearly confirmed using experiments with resting cells. The model was used to compare the kinetics of citrate consumption between several strains of Leuconostoc mesenteroides subsp. mesenteroides, Leuconostoc mesenteroides subsp. cremoris and Leuconostoc lactis.