1,720,969 research outputs found
Models for enzyme superactivity in aqueous solutions of surfactants
No full textTheoretical models are developed here for enzymic activity in the presence of direct micellar aggregates. An approach similar to that of Bru et al. [Bru, Sánchez-Ferrer and Garcia-Carmona (1989) Biochem. J. 259, 355–361] for reverse micelles has been adopted. The system is considered to consist of three pseudo-phases: free water, bound water and surfactant tails. The substrate concentration in each pseudo-phase is related to the total substrate concentration in the reaction medium. In the absence of interactions between the enzyme and the micelles, the model predicts either monotonically increasing or monotonically decreasing trends in the calculated reaction rate as a function of surfactant concentration. With enzyme–micelle interactions included in the formulation (by introducing an equilibrium relation between the enzyme confined in the free water and in the bound water pseudo-phases, and by allowing for different catalytic behaviours for the two forms), the calculated reaction rate can exhibit a bell-shaped dependence on surfactant concentration. The effect of the partition of enzyme and substrate is described, as is that of enzyme efficiency in the various pseudo-phases
Studying enzyme-catalyzed depolymerizations in continuous reactors
No full textThe models of Ohmine et al. and Sendra and Carbonell for the enzymatic breakdown of polymers in batch reactors were modified to describe the depolymerization in continuous reactors. The model equations give the time course of the product concentration in the reactor permeate and that of the total product. The model predictions were compared with the experimental results for the hydrolysis of polygalacturonic acid in ultrafiltration membrane reactors. The amount of enzyme in the reactor varied from 0.18 to 1.80 mg. The residence time (100 min), temperature (25 degreesC), and membrane molecular cutoff (30 kDa) were maintained constant in the experiments. The system response was sensitive to the kinetic pattern of the enzymatic attack and was in reasonable agreement only with the predictions of the model based on the kinetic assumption made by Sendra and Carbonell. An induction period and an asymptotic amount of product were detected, which cannot be explained by the model of Ohmine et al
Effect of cationic and non-ionic surfactants on the hydrolysis of N-glutaril –L-phenylalanine catalysed by chymotrypsin iso-enzymes
No full textThe hydrolysis of N-glutaryl-l-phenylalanine p-nitroanilide catalysed by various chymotrypsin (CT) iso-enzymes (α-CT, β-CT, δ-CT, and γ-CT) has been studied in the presence of cationic and non-ionic surfactants at concentration higher than the critical micellar concentration. The enzyme activity was tested in the presence of the following surfactants: cetyltrimethylammonium bromide (CTABr), cetyldimethylethylammonium bromide (CDMEABr), cetyltripropylammonium bromide (CTPABr), Triton X100 (TX100) and polyoxyethylene 9 lauryl ether (PO9). The activity of the iso-enzymes depends on the surfactant concentration and it varies with the surfactant head group dimensions (CTPABr>CDMEABr>CTABr). For all the iso-enzymes, superactivity has been detected only in the presence of CTPABr and CDMEABr. The extent of superactivity depends on the enzyme used (δ-CT>β-CT>γ-CT>α-CT). The observed reaction rate has been compared with the prediction of a theoretical model for enzymatic activity in the presence of surfactant aggregates in aqueous media developed in a previous paper. The results can be explained by introducing an equilibrium relation between the enzyme confined in the free bulk water and in the bound water pseudo-phase, and by allowing for different catalytic behaviours of the two forms of enzyme.
The theoretical model enables the initial reaction rate to be related to the substrate concentration with an overall Michaelis–Menten equation. Good agreement has been found between experimental and model predicted values of the kinetic parameters.
© 2002 Elsevier Science B.V. All rights reserved
Use of cationic additives to enhance a-chymotrypsin activity in the hydrolysis of N-glutaryl-L-phenylalanine: kinetic and modelling study
No full textA comparative study on free and poly-HEMA immobilized lipase in a transesterification reaction
No full textStudying enzyme-catalized depolymerizations in continuous reactors
No full textThe models of Ohmine et al. and Sendra and Carbonell for the enzymatic breakdown of polymers in batch reactors were modified to describe the depolymerization in continuous reactors. The model equations give the time course of the product concentration in the reactor permeate and that of the total product. The model predictions were compared with the experimental results for the hydrolysis of polygalacturonic acid in ultrafiltration membrane reactors. The amount of enzyme in the reactor varied from 0.18 to 1.80 mg. The residence time (100 min), temperature (25 °C), and membrane molecular cutoff (30 kDa) were maintained constant in the experiments. The system response was sensitive to the kinetic pattern of the enzymatic attack and was in reasonable agreement only with the predictions of the model based on the kinetic assumption made by Sendra and Carbonell. An induction period and an asymptotic amount of product were detected, which cannot be explained by the model of Ohmine et al. Copyright © 2001 American Chemical Societ
Polygalacturonic Acid/endo-Polygalacturonase System: A Kinetic Study in Batch Reactors
No full textThe enzymatic depolymerization of the pectic substance polygalacturonic acid (PGA) is studied in batch reactor. The number-average molecular weight of native substrate is estimated, using a simple and quick technique, to be approximately 11.1 kDa, the polymeric chains consisting on average of 63 galacturonic acid units. The effect of enzyme concentration was studied varying biocatalyst loading from 6 to 242 mg/L. The experiments were repeated at substrate concentrations ranging from 0.5 to 5 g/L. Data obtained at both short reaction time (20 min) and prolonged enzyme action (up to 350 min) are correlated using different kinetic equations, and the parameter values are discussed
Operational stability of Brevibacterium imperialis CBS 489-74 nitrile hydratase
No full textBrevibacterium imperialis CBS 489-74 was grown in broths prepared with yeast and malt extract, bacteriological peptone and 2% glucose or differently modified with the addition of Na-phosphate buffer, FeSO4, MgSO4 and CoCl2. The peak production of nitrile hydratase (NHase) did not change significantly. At the stationary growth phase, the units per milliliter of broth (60 units ml−1) were more important than those at the exponential growth phase.
The NHase operational stability of whole resting cells was monitored following the bioconversion of acrylonitrile to acrylamide in continuous and stirred UF-membrane reactors. The rate of inactivation was independent on buffer molarity from 25 to 75 mM and on pH from 5.8 to 7.4. Enzyme stability and activity remained unchanged in distilled water. The initial reaction rate increased from 12.8 to 23.8 g acrylamide/g dry cell/h, but NHase half-life dropped from 33 to roughly 7 h when temperature was varied from 4°C to 10°C. The addition of butyric acid up to 20 mM did not improve enzyme operational stability, and largely reduced (94%) enzyme activity. Acrylonitrile caused an irreversible damage to NHase activity. High acrylonitrile conversion (86%) was attained using 0.23 mg cells/ml in a continuously operating reactor
New experimental procedure for monitoring molecular weight breakdown during enzymatic degradation of polygalacturonic acid in continuous membrane reactors
No full textThe enzymatic depolymerization of polygalacturonic acid was studied in a continuous stirred UF membrane reactor. Experimental data were obtained in different runs with varying amounts of biocatalyst from 0.25 to 1.35 mg. The residence time (1.7 h), temperature (25 °C), and membrane molecular weight cutoff (30 kDa) were kept constant. The time course of the oligomeric product concentration in the output solution was correlated with a model equation, that was originally developed for batch reactions and modified for the continuous system. A new experimental method was used to detect the instantaneous mean molecular weight. Evidence was obtained that the enzymatic breakdown was almost complete within 2−3 h from the startup of the bioreaction. The proposed method proved to be sufficiently accurate and easy to employ for rapid on-line control of the industrial bioprocess. Copyright © 2003 American Chemical Societ
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