scholarly journals The effect of substrate partitioning on the kinetics of enzymes acting in reverse micelles

1990 ◽  
Vol 268 (3) ◽  
pp. 679-684 ◽  
Author(s):  
R Bru ◽  
A Sánchez-Ferrer ◽  
F García-Carmona
Keyword(s):  
Reverse Micelle ◽  
Substrate Concentration ◽  
Reverse Micelles ◽  
Bound Water ◽  
Free Water ◽  
Enzymic Activity ◽  
Molar Ratio ◽  
Biphasic Model ◽  
Catalytic Constant ◽  
Kinetics Of

A theoretical model for the expression of enzymic activity in reverse micelles previously developed [Bru. Sánchez-Ferrer & García-Carmona (1989) Biochem. J. 259, 355-361] was extended in the present work. The substrate concentration in each reverse-micelle phase (free water, bound water and surfactant apolar tails) and the organic solvent was expressed as a function of the total substrate concentration, taking into account its partition coefficients, that is, partitioning of the substrate in a multiphasic system. In each phase the enzyme expresses a catalytic constant and a Km. Thus the whole reaction rate is the addition of the particular rates expressed in each domain. This model was compared with that developed for a biphasic system [Levashov, Klyachko, Pantin, Khmelnitski & Martinek (1980) Bioorg. Khim. 6, 929-943] by fitting the experimental results obtained with mushroom tyrosinase (working on both 4-t-butylcatechol and 4-methylcatechol) to the two models. The parameters which characterize reverse micelles, omega 0 (water/surfactant molar ratio) and theta (fraction of water) were investigated. The omega 0 profile was shown to be hyperbolic for both substrates. Activity towards 4-t-butylcatechol decreases as theta increases, this observation being attributable to a dilution of the substrate. A Km of 7.8 M for 4-t-butylcatechol could be calculated on the basis of the biphasic model, whereas it was 13.5 mM when calculating on the basis of our model. A new parameter, rho (= [substrate]/theta), was defined to characterize those substrates that mainly solubilize in the reverse micelle (‘micellar substrates’).

scholarly journals A theoretical study on the expression of enzymic activity in reverse micelles

1989 ◽  
Vol 259 (2) ◽  
pp. 355-361 ◽  
Author(s):  
R Bru ◽  
A Sánchez-Ferrer ◽  
F Garcia-Carmona
Keyword(s):  
Reverse Micelle ◽  
Reverse Micelles ◽  
Structural Model ◽  
Dynamic Equilibrium ◽  
Free Water ◽  
Continuous Phase ◽  
Enzymic Activity ◽  
Water Dynamics ◽  
Polar Phase ◽  
Catalytic Constant

The present work deals with a theoretical model of catalysis by enzymes entrapped in reverse micelles. Three aspects of the enzyme-reverse-micelle system have been considered: structure, dynamics and enzyme distribution and catalysis in reverse micelles. A proposed structural model of reverse micelles [El Seoud (1984) in Reverse Micelles (Luisi, P. L. & Straub, B. E., eds.), p. 81, Plenum Press, New York] consists of three domains: surfactant apolar tails, bound water and free water. Dynamics are based on a dynamic equilibrium of association-dissociation that lead one to consider the dispersed polar phase as a pseudo-continuous phase [Luisi, Giomini, Pileni & Robinson (1988) Biochim. Biophys. Acta 947, 207-246]. Enzyme is distributed among the reverse-micelle domains and it expresses a catalytic constant for each one of them. The overall activity is calculated taking into account the volume in which enzyme is solubilized, and expressed as a function of the whole volume (V). The characteristic parameters of reverse micelles, omega 0 (= [H2O]/[surfactant]) and theta (= % water, v/v), were investigated as modulators of enzymic activity. Three basic patterns of modulation by omega 0 were found depending on which domain the enzyme expressed the highest catalytic constant. Combinations of those basic patterns lead to other modulation types that can be found experimentally, such as superactivation. Other combinations predict behaviour patterns not described to date, such as superinhibition. Dependence of catalytic activity on theta was only stated at omega 0 values around a critical value, which coincides with the appearance of free water.

scholarly journals Models for enzyme superactivity in aqueous solutions of surfactants

1999 ◽  
Vol 344 (3) ◽  
pp. 765-773 ◽  
Author(s):  
Paolo VIPARELLI ◽  
Francesco ALFANI ◽  
Maria CANTARELLA
Keyword(s):  
Substrate Concentration ◽  
Surfactant Concentration ◽  
Reaction Rate ◽  
Reaction Medium ◽  
Bound Water ◽  
Free Water ◽  
Theoretical Models ◽  
Enzymic Activity ◽  
Equilibrium Relation ◽  
Micellar Aggregates

Theoretical 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.

Preparation and Properties of a Water-Swelling Rubber by in situ Formed Lithium Acrylate in Nitrile Rubber

2005 ◽  
Vol 13 (2) ◽  
pp. 181-190 ◽  
Author(s):  
Wentan Ren ◽  
Zonglin Peng ◽  
Yong Zhang ◽  
Yinxi Zhang
Keyword(s):  
Mechanical Properties ◽  
Bound Water ◽  
Free Water ◽  
High Water ◽  
Nitrile Rubber ◽  
Molar Ratio ◽  
Scanning Calorimetry ◽  
Swelling Properties ◽  
Water Swelling

Lithium acrylate (LiAA) was in situ prepared in nitrile rubber (NBR) through neutralization of lithium hydroxide (LiOH) and acrylic acid (AA) during mixing. The NBR/LiAA compounds were vulcanized with dicumyl peroxide (DCP). The in situ preparation and polymerization of LiAA were characterized using Fourier transform infrared (FTIR) spectrometer. The micrographs of the compounds and vulcanizates were explored using a scanning electron microscope (SEM). The effects of DCP and LiAA contents on the water-swelling and mechanical properties of the vulcanizates were studied. The relationship between the LiOH/AA molar ratio and the properties of the vulcanizates was investigated. The results showed that the in situ formed LiAA could improve the mechanical properties and water–swelling properties of the NBR/LiAA vulcanizates. The vulcanizates properly compounded had high water-swelling ratio over 800% and tensile strength more than 12MPa. The differential scanning calorimetry (DSC) measurements indicated that the water absorbed in the vulcanizate existed in PLiAA and NBR networks in three different physical states, namely, free water, freezable bound water and non-freezable bound water.

scholarly journals Application of active-phase plot to the kinetic analysis of lipoxygenase in reverse micelles

1992 ◽  
Vol 288 (3) ◽  
pp. 1011-1015 ◽  
Author(s):  
M Perez-Gilabert ◽  
A Sanchez-Ferrer ◽  
F Garcia-Carmona
Keyword(s):  
Reverse Micelles ◽  
Octadecadienoic Acid ◽  
Active Phase ◽  
Enzyme Concentration ◽  
Enzymic Activity ◽  
Relative Volume ◽  
Soya Bean ◽  
Molar Ratio ◽  
Complex Activity ◽  
Micelle Size

A new plot for explaining the complex expression of the enzymic activity in reverse micelles has been developed as an extension of the theoretical model described by our group [Bru, Sánchez-Ferrer & García-Carmona (1990) Biochem. J. 268, 679-684]. The plot describes the changes in the relative volume, amount of enzyme (mumoles), enzyme concentration (microM) and substrate concentration (microM) in the phase where the enzyme is active. To illustrate the usefulness of this plot, the complex activity of soya bean lipoxygenase in reverse micelles acting on its interfacial substrate, octadecadienoic acid, was studied. It showed the key parameters ruling the activity profiles of lipoxygenase with respect to micelle size (omega 0), micelle concentration (theta) and the substrate/surfactant molar ratio (rho), which have never been described before.

scholarly journals Kinetics of ascorbic acid loss during thermal treatment in different pH buffer solutions and the presence of oxygen

Food Research ◽  
2020 ◽  
Vol 4 (5) ◽  
pp. 1513-1519
Author(s):  
N.M. Thuy ◽  
H.T.N. Ha ◽  
N.V. Tai
Keyword(s):  
Ascorbic Acid ◽  
Thermal Treatment ◽  
Oxygen Concentration ◽  
Degradation Kinetics ◽  
Thermal Degradation Kinetics ◽  
Molar Ratio ◽  
Aerobic Degradation ◽  
Prolonged Heating ◽  
Biphasic Model ◽  
Kinetics Of

Ascorbic acid stability is greatly influenced by temperature, oxygen content. Both exposures to oxygen and prolonged heating in the presence of oxygen destroy ascorbic acid. Thermal degradation kinetics of ascorbic acid in sodium acetate buffer (0.2 M, pH 5.0) and sodium phosphate buffer (0.1 M, pH 7.0) were studied at the temperature range of 80 to 100°C and the different molar ratio between oxygen and ascorbic acid. The obtained results showed that the decrease in AA concentration as a function of time at constant temperature occurred in two phases. The biphasic model was used to describe the loss of AA in aqueous solution due to thermal treatment. The AA degradation had occurred during thermal processing probably due to oxidation (aerobic degradation). When the oxygen was totally used up, the anaerobic degradation dominated and took place much more slowly than aerobic degradation. At low AA concentration (≈0.28 mM) and an oxygen concentration of 0.25 mM, most of the degradation of AA occurred under aerobic conditions, however, AA was further degraded through an anaerobic pathway at a higher ratio of AA to oxygen concentration [0.57:0.25 (mM:mM) and 1.42:0.25 (mM:mM)]. The estimated activated energy Ea values, the temperature sensitivity of the kvalues was lower at pH 7.0 than at pH 5.0. Studying the degradation of ascorbic in a model system is essential in order to fully understood and applied effectively in food products processing.

Carbon tetrachloride biodegradation in a fixed-biofilm reactor and its kinetic study

1998 ◽  
Vol 38 (8-9) ◽  
pp. 155-162 ◽  
Author(s):  
G. Jin ◽  
A. J. Englande
Keyword(s):  
Carbon Tetrachloride ◽  
Continuous Flow ◽  
Model Comparison ◽  
Biofilm Reactor ◽  
Pseudomonas Cepacia ◽  
Initial Concentration ◽  
Biphasic Model ◽  
Providencia Stuartii ◽  
Kinetics Of ◽  
Fixed Biofilm

Kinetics of Carbon Tetrachloride biodegradation are evaluated in a continuous-flow fixed-biofilm reactor with controlled initial redox potential. The column was seeded with a mixed culture of indigenous microorganisms Pseudomonas cepacia and Providencia stuartii. The fixed biofilm reactor exhibited 98%–99.9% biodegradation of CT introduced into the reactor at an initial concentration of about 200 μg/l for retention times of 1 to 4 days respectively. Four models were employed to evaluate the kinetics of CT biodegradation. These included: Eckenfelder (1989), Arvin (1991), Bouwer and McCarty (1985) and a biphasic model. Comparison of calculated results with observed results between these models agreed very closely to each other (0.968 < R2 < 0.999). Predicted performance was best described by the model of Bouwer and McCarty (1985). However, the biphasic and Eckenfelder models provided excellent correlations and were much simpler to apply. The biphasic model yielded very good correlations of the data for all detention times evaluated; whereas, the Eckenfelder model effected comparable results only at the longer retention times studied.

Determine the Moisture Distribution in Sewage Sludge by Drying Differential

2014 ◽  
Vol 665 ◽  
pp. 404-407 ◽  
Author(s):  
Wan Yu ◽  
Pei Sheng Li
Keyword(s):  
Sewage Sludge ◽  
Interstitial Water ◽  
Bound Water ◽  
Free Water ◽  
High Accuracy ◽  
Moisture Distribution ◽  
Municipal Sewage ◽  
Municipal Sewage Sludge ◽  
Hot Air ◽  
Critical Water Content

Moisture distribution in sewage sludge was considered as the essential of thermal drying. Some methods were given in literatures to test the moisture distribution, but there was no standard method to determine the critical water content between different kinds of water. The municipal sewage sludge was dried by hot air in this work. Based on the drying curve, the derivative of drying rate with respect to dry basis moisture content was brought out to analyze the moisture distribution in sewage sludge. Results show that this method can easily determine the free water, interstitial water, surface water and bound water with a high accuracy. The present work can provide new insight to determine the moisture distribution in sewage sludge, which was still lacking in the literatures.

scholarly journals Initiation and propagation kinetics of inhibited lipid peroxidation

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Reza Farhoosh
Keyword(s):  
Lipid Peroxidation ◽  
Reverse Micelles ◽  
Fish Oils ◽  
Lipid Hydroperoxides ◽  
Critical Concentrations ◽  
Initial Values ◽  
Initiation And Propagation ◽  
Kinetics Of

AbstractEffect of hydroxytyrosol (HT) and tert-butylhydroquinone (TBHQ) on the kinetics of lipid hydroperoxides (LOOH) accumulation during the initiation and propagation peroxidations of canola and fish oils at 60 °C was studied. The initiation kinetics of the inhibited peroxidation indicated considerable relative activities, A, for HT and TBHQ in the canola (> 3200 and > 27,000, respectively) and fish (> 120 and > 5000, respectively) oils. The critical concentrations of LOOH reverse micelles (CMCL = 33 mM and 57 mM in the canola and fish, respectively, oils) significantly decreased, on average, to about one-third and 8% of the initial values for HT and TBHQ, respectively. Interestingly, the propagation kinetics of the inhibited peroxidation demonstrated that the antioxidants were still able to inhibit peroxidation, so that the relative propagation oxidizability parameter Rn′ was significantly improved to < 0.5 for HT and to < 0.2 for TBHQ in the canola and fish, respectively, oils.

scholarly journals The apparent Km is a misleading kinetic indicator

1986 ◽  
Vol 239 (1) ◽  
pp. 175-178 ◽  
Author(s):  
I W Plesner
Keyword(s):  
Substrate Concentration ◽  
Kinetic Data ◽  
Substrate Binding ◽  
Enzymic Activity ◽  
Free Enzyme ◽  
Ligand Concentration ◽  
Double Reciprocal Plot ◽  
Michaelis Constant ◽  
Formal Framework ◽  
Enzyme Species

When information concerning whether or not a ligand interacts with the same enzyme species as do the substrates, the variation of the Michaelis constant Km (for each substrate) with ligand concentration is sometimes used as a diagnostic. It is shown that the Michaelis constant is of no particular value in this respect and may be misleading. Thus, depending on the mechanism, Km may vary with ligand concentration even though the ligand interacts with species far removed in the mechanism from the substrate-binding steps, and it may stay constant in cases where the ligand competes directly for the free enzyme. In contrast, the slope of a double-reciprocal plot of the kinetic data (= Km/Vmax.) (or, equivalently, the ordinate intercept of a Hanes plot A/v versus A, where A is the substrate concentration) independently of the particular mechanism involved uniquely signifies whether or not such interaction occurs. The results clearly indicate that, for purposes other than communicating the substrate concentration yielding control of the enzymic activity, usage of Km and its variation with ligand concentration should be avoided and interest instead focused on the slope, in accordance with the long-established rules of Cleland [Biochim. Biophys. Acta (1963) 67, 188-196], for which the present analysis provides the formal framework.

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