Kinetic Behavior (kinetic + behavior)

Distribution by Scientific Domains
Distribution within Chemistry


Selected Abstracts


KINETIC BEHAVIOR OF SOYBEAN LIPOXYGENASE: A COMPARATIVE STUDY OF THE FREE ENZYME AND THE ENZYME IMMOBILIZED IN AN ALGINATE SILICA SOL-GEL MATRIX,

JOURNAL OF FOOD BIOCHEMISTRY, Issue 1 2000
AN-FEI HSU
Lipoxygenase (LOX) is an enzyme that regioselectively introduces a hydroperoxide into polyunsaturated fatty acids (PUFA). We recently reported a procedure that immobilizes soybean LOX within an alginate sol-gel matrix. In this study, the kinetic profile of free LOX was compared with that of the sol-gel immobilized LOX. The temperature dependent activity profile of free LOX was optimal at 25C whereas immobilized LOX had optimal activity over the temperature range of 25,35C. Enzyme activity, measured in aqueous buffer, for both the free and immobilized LOX preparations had Km values of 2.5 and 1.40 mmoles/L, respectively, and Vmax values of 0.056 and 0.02 ,mol/min, respectively. The relative rates of oxidation of linoleic acid and acylgfycerols containing linoleoyl residues catalyzed by free and immobilized LOX also were determined The results showed that both free and immobilized LOX favor linoleic acid as a substrate. Relative substrate preference for free LOX was linoleic acid >1-monolinolein > 1,3-dilinolein >trilinolein, and for immobilized LOX was linoleic acid >l, 3-dilinolein >1-monolinolein >trilinolein. In general, LOX immobilized in alginate silica sol-gel matrix retained the physical and chemical characteristics of free LOX. [source]


Kinetic behavior of ethylene/1-hexene copolymerization in slurry and solution reactors

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2005
Long Wu
Abstract The copolymerization of ethylene and 1-hexene over a spherical polymer/MgCl2 -supported TiCl4 catalyst was studied as a function of the polymerization temperature from 40 to 100 °C in a slurry reactor and from 120 to 200 °C in a solution reactor with triethylaluminum (TEA) as a cocatalyst (1.0,6.8 mmol). The activities increased from 40 to 80 °C and then declined monotonically with increases in the temperature during the slurry and solution polymerizations. The kinetic behavior in the slurry and solution operations was described by the same rate expression. The modeling results indicated that the catalyst had at least two different types of catalytic sites; one site was responsible for the acceleration,decay nature of the activity profiles, whereas the second site resulted in long-term activity. The apparent activation energy for site activation in the slurry operation was 69.9 kJ/mol; no activation energies for site activation could be estimated for the solution operation because the activation process was essentially instantaneous at the higher temperatures. The activation energies for deactivation were 100.3 kJ/mol for the slurry operation and 31.2 kJ/mol for the solution operation. The responses to TEA were similar for the slurry and solution operations; the rates increased with increasing amounts of TEA between 1.0 and 3.4 mmol and then decreased with larger amounts of TEA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2248,2257, 2005 [source]


Substrate-dependent hysteretic behavior in StEH1-catalyzed hydrolysis of styrene oxide derivatives

FEBS JOURNAL, Issue 24 2008
Diana Lindberg
The substrate selectivity and enantioselectivity of Solanum tuberosum epoxide hydrolase 1 (StEH1) have been explored by steady-state and pre-steady-state measurements on a series of styrene oxide derivatives. A preference for the (S)- or (S,S)-enantiomers of styrene oxide, 2-methylstyrene oxide and trans -stilbene oxide was established, with E -values of 43, 160 and 2.9, respectively. Monitoring of the pre-steady-state phase of the reaction with (S,S)-2-methylstyrene oxide revealed two observed rates for alkylenzyme formation. The slower of these rates showed a negative substrate concentration dependence, as did the rate of alkylenzyme formation in the reaction with the (R,R)-enantiomer. Such kinetic behavior is indicative of an additional, off-pathway step in the mechanism, referred to as hysteresis. On the basis of these data, a kinetic mechanism that explains the kinetic behavior with all tested substrates transformed by this enzyme is proposed. Regioselectivity of StEH1 in the catalyzed hydrolysis of 2-methylstyrene oxide was determined by 13C-NMR spectroscopy of 18O-labeled diol products. The (S,S)-enantiomer is attacked exclusively at the C-1 epoxide carbon, whereas the (R,R)-enantiomer is attacked at either position at a ratio of 65 : 35 in favor of the C-1 carbon. On the basis of the results, we conclude that differences in efficiency in stabilization of the alkylenzyme intermediates by StEH1 are important for enantioselectivity with styrene oxide or trans -stilbene oxide as substrate. With 2-methylstyrene oxide, slow conformational changes in the enzyme also influence the catalytic efficiency. [source]


Identification of catalytically important residues in the active site of Escherichia coli transaldolase

FEBS JOURNAL, Issue 8 2001
Ulrich Schörken
The roles of invariant residues at the active site of transaldolase B from Escherichia coli have been probed by site-directed mutagenesis. The mutant enzymes D17A, N35A, E96A, T156A, and S176A were purified from a talB -deficient host and analyzed with respect to their 3D structure and kinetic behavior. X-ray analysis showed that side chain replacement did not induce unanticipated structural changes in the mutant enzymes. Three mutations, N35A, E96A, and T156A resulted mainly in an effect on apparent kcat, with little changes in apparent Km values for the substrates. Residues N35 and T156 are involved in the positioning of a catalytic water molecule at the active site and the side chain of E96 participates in concert with this water molecule in proton transfer during catalysis. Substitution of Ser176 by alanine resulted in a mutant enzyme with 2.5% residual activity. The apparent Km value for the donor substrate, fructose 6-phosphate, was increased nearly fivefold while the apparent Km value for the acceptor substrate, erythrose 4-phosphate remained unchanged, consistent with a function for S176 in the binding of the C1 hydroxyl group of the donor substrate. The mutant D17A showed a 300-fold decrease in kcat, and a fivefold increase in the apparent Km value for the acceptor substrate erythrose 4-phosphate, suggesting a role of this residue in carbon,carbon bond cleavage and stabilization of the carbanion/enamine intermediate. [source]


Thermal decomposition of cyclic organic peroxides in pure solvents and binary solvent mixtures

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2010
Mariángeles Iglesias
The thermal decomposition reaction of acetone cyclic triperoxide, acetone cyclic diperoxide, 4-heptanone cyclic diperoxide, and pinacolone cyclic diperoxide ca. 0.02 M was studied in pure solvents (acetone and 1-propanol) and in binary mixtures of acetone/1-propanol at 150°C. The kinetics of each system was explored by gas chromatography (GC) at different solvent compositions. The reactions showed a behavior accordingly with a pseudo-first-order kinetic law up to at least 90% peroxide decomposition. The main organic products derived from these thermolysis reactions were detected by GC analysis. Among them, the corresponding ketones, methane, ethane, and propane were the main identified products. The rates of decomposition of pinacolone diperoxide in the pure solvents were practically independent of the solvent characteristics, so it was of no interest to analyze its kinetic behavior in binary solvent mixtures. In acetone/1-propanol mixtures, the solvation effect on the cyclic peroxides derived from 4-heptanone and acetone molecules was slightly dominated by specific interactions between 1-propanol and a diradical-activated complex initially formed. This species was preferentially solvated by 1-propanol instead of acetone. Specific interactions between the O atoms from the peroxidic bond and the H from the OH in 1-propanol can be taken into account. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 347,353, 2010 [source]


Effect of surfactant micelles on the kinetics of oxidation of D -fructose by cerium(IV) in sulfuric acid medium

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2006
Kabir-ud-Din
Kinetics of the oxidation of D -fructose by cerium(IV) has been investigated both in the absence and presence of surfactants (cetyltrimethylammonium bromide, CTAB, and sodium dodecyl sulfate, SDS) in sulfuric acid medium. The reaction exhibits first-order kinetics each in [cerium(IV)] and [D -fructose] and inverse first order in [H2SO4]. The Arrhenius equation is found to be valid for the reaction between 30,50°C. A detailed mechanism with the associated reaction kinetics is presented and discussed. While SDS has no effect, CTAB increases the reaction rate with the same kinetic behavior in its presence. The catalytic role of CTAB micelles is discussed in terms of the pseudophase model proposed by Menger and Portnoy. The association constant Ks that equals to 286 mol,1 dm3 is found for the association of cerium(IV) with the positive head group of CTAB micelles. The effect of inorganic electrolytes (Na2SO4, NaNO3, NaCl) has also been studied and discussed. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 18,25, 2006 [source]


First-order stochastic cellular automata simulations of the lindemann mechanism

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2004
Chad A. Hollingsworth
The Lindemann mechanism explains how apparent unimolecular chemical reactions arise from bimolecular collisions. In this mechanism an ingredient M activates reactants A through collisions, and the resulting activated species A* can either decay to products P or be deactivated back to A, again via collisions with M. A first-order stochastic cellular automata model described previously [Seybold, Kier, and Cheng, J Chem Inf Comput Sci 1997, 37, 386] has been modified to simulate this mechanism. It is demonstrated that this model accurately reflects the salient features of the Lindemann mechanism, including the normal second-order kinetic behavior at low [M] and apparent first-order kinetics at high [M]. At low [M] the mechanism is equivalent to a rate-limited sequential process, whereas at high [M] it becomes a preequilibrium with leakage to products. The model also allows an examination of the validity of the steady-state approximation normally employed in a deterministic analysis of this mechanism, and it is seen that this approximation is not well justified under reasonable conditions. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 230,237 2004 [source]


Mannich-Type Reactions Catalyzed by Neutral Salts in Water

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11 2003
Catherine Loncaric
Abstract Mannich-type reactions of imines with silicon enolates were found to be catalyzed by neutral salts such as sodium triflate in water as a suspension medium. Unusual kinetic behavior indicates that the presence of the Mannich adduct facilitates the rate of its formation. [source]


Abnormal kinetic behavior of uroporphyrinogen decarboxylase obtained from rats with hexachlorobenzene-induced porphyria

JOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 1 2005
Gabriela Chaufan
Abstract Uroporphyrinogen decarboxylase is an essential enzyme in all organisms and functions in the heme biosynthetic pathway, catalyzing the decarboxylation of the four acetate groups of uroporphyrinogen to form coproporphyrinogen. This work examines whether the four sequential decarboxylations occur at the same active site, and explores whether hexachlorobenzene-induced porphyria affects the behavior of the enzyme. For this purpose, kinetic competition studies were done with mixtures of uroporphyrinogen III and pentacarboxyporphyrinogen III. With the enzyme from normal rats, a constant velocity was obtained with all the mixtures, indicating that uroporphyrinogen and pentacarboxy-porphyrinogen react at the same active site, i.e. the first and fourth decarboxylations occur at the same site. In contrast, in experiments with enzyme from rats with hexachlorobenzene-induced porphyria, the total rate for mixtures was always lower than the reference rate; and a curve with a deep minimum was obtained, indicating that the two reactions occur at functionally different sites, but with cross-inhibition. This suggests that the modifications induced in the enzyme by hexachlorobenzene cause the two active sites to become nonequivalent and functionally different. The question is discussed how the hexachlorobenzene treatment may produce this abnormal kinetic behavior, and alternative hypotheses are considered. © 2005 Wiley Periodicals, Inc. J Biochem Mol Toxicol 19:19,24, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20055 [source]


Temperature dependency of granule characteristics and kinetic behavior in UASB reactors

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 8 2004
Hsin-Hsien Chou
Abstract When an inhibitory substrate, phenol, was treated under mesophilic conditions (25, 30, 35, and 40 °C), the upflow anaerobic sludge bed (UASB) reactors at 30 °C resulted in the greatest amount of biomass and the largest granule size, while the UASB reactors at 25 °C resulted in the smallest granule size and the greatest amount of wash-out of sludge. The granule size tended to be negatively correlated with the amount of wash-out of sludge. With an increase in temperature, the kinetic constant k for anaerobic phenol degradation increased and the half saturation constant (Ks) decreased. The mass fraction of methanogens (f) increased with increasing operational temperature in the UASB reactors and the activation energy (Ea) for acetate methanogenesis was larger than that for phenol acidogenesis in the batch reactors, indicating that the operational temperature imposes a more influential effect on methanogens than on acidogens. From the results of the activity of acidogens and methanogens (expressed in specific COD utilization rate), the rate-limiting step is phenol acidogenesis. Copyright © 2004 Society of Chemical Industry [source]


Reduction of Acrylamide and Its Kinetics by Addition of Antioxidant of Bamboo Leaves (AOB) and Extract of Green Tea (EGT) in Asparagine,Glucose Microwave Heating System

JOURNAL OF FOOD SCIENCE, Issue 2 2008
Yu Zhang
ABSTRACT:, This study investigated the effect of antioxidant of bamboo leaves (AOB) and extract of green tea (EGT) on the formation and kinetics of acrylamide in an equimolar asparagine,glucose model system. The substrates spiked with AOB and EGT were microwave-heated at 180 °C and the acrylamide content in final reaction products was quantified by ultra-performance liquid chromatography,tandem mass spectrometry (UPLC-MS/MS). The results showed that both AOB and EGT could effectively reduce the formation of acrylamide in an asparagine,glucose microwave heating model system and achieved a maximum reduction rate when the addition levels of AOB and EGT were both 10,6 mg/mL reaction solution. To describe the kinetic behavior of acrylamide, a simplified kinetic model was optimized and relative kinetic rate constants were evaluated under isothermal conditions. The results indicated that the reduction effect of AOB and EGT on the acrylamide formation may partly be ascribed to the decrease of the formation rate constant (kF) in both AOB and EGT-spiked systems (43.4% and 32.3% of decrease, respectively, P < 0.05). The kinetic parameter kE, which represents the elimination rate of acrylamide in both AOB and EGT-spiked systems, was not significantly different (6.9% of increase and 10.9% of decrease, respectively, P > 0.05). The results of the kinetic study indicated that addition of AOB and EGT could significantly reduce the formation rate constant (kF) of acrylamide, but could not significantly affect the elimination rate constant (kE) of acrylamide. [source]


Kinetics of styrene emulsion polymerization above the critical micelle concentration: Effect of the initial monomer concentration on the molecular weight

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2005
Jorge Herrera-Ordonez
Abstract The emulsion polymerization of styrene above the critical micelle concentration has been experimentally studied from a low final polymer content up to a high polymer content (,50%). A maximum in the molecular weight (M) evolution has been observed in all cases. The presence or absence of such a maximum depends on the relative values of the rate of free-radical entry (,) and the rate of chain transfer to the monomer (KtrCMp, where Ktr is the chain transfer to monomer rate coefficient and CMp is the monomer concentration in particles). If , , KtrCMp, M is constant and equal to Kp/Ktr (where Kp is the propagation rate coefficient), except at very low particles sizes typical of the early stages of the reaction, in which the chain length is limited by the particle size. On the other hand, if , , KtrCMp, M is determined by both CMp and ,. It is proposed that , is determined by the sum of the entry of the oligomeric radicals formed in the aqueous phase and those contained in particles that undergo limited coagulation. This coagulative entry can become very significant; therefore, reactor hydrodynamics can play a major role in the kinetic behavior observed. Disagreement between Clay and Gilbert's model and molecular weight distribution data can be ascribed, to a lesser or greater extent, to the degree of correctness of the quasi-steady-state and instantaneous-termination approaches. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1963,1972, 2005 [source]


Study on the Kinetics for Enzymatic Degradation of a Natural Polysaccharide, Konjac Glucomannan

MACROMOLECULAR SYMPOSIA, Issue 1 2004
Guangji Li
Abstract The enzymatic degradation of konjac glucomannan (KGM) was conducted using ,-mannanase from an alkalophilic Bacillus sp. in the aqueous medium (pH 9.0) at 30°C. The intrinsic viscosity ([,]), molecular weight (Mw) and molecular weight distribution (MWD) of the degraded KGM were measured. The mathematical relation between [,] and Mw, [,] = 5.06 × 10,4Mw0.754, was established. The kinetic analysis reveals a dependence of the rate constant (k) on the period of reaction and the initial substrate concentration (c0) over the range of substrate concentration (1.0,2.0%) used in this work. The results indicate that the enzymatic degradation of KGM is a complex reaction combining two reaction processes with different orders. In the initial phase of degradation k is inversely proportional to c0, which is characteristic of a zeroth-order reaction; while in the following phase k is independent of c0, implying the degradation follows a first-order reaction. The reactivity difference in breakable linkages of KGM, the action mechanism of an enzyme on KGM macromolecules, and the theory concerning the formation of an enzyme-substrate complex and ,substrate saturation' can be used to explain such a kinetic behavior. In addition, the enzymatic degradation of KGM was also carried out using the other enzymes like ,-mannanase from a Norcardioform actinomycetes, ,-glucanase Finizym and a compound enzyme Hemicell as a biocatalyst. By comparing and analyzing the degradation processes of KGM catalyzed by four different enzymes, it can be observed that there is a two-stage reaction with two distinct kinetic regimes over a certain range of degradation time for each of the degradation processes. These results are useful to realize controllable degradation of polysaccharides via an environmental benign process. [source]


Comparative analysis of gene expression on mRNA and protein level during development of Streptomyces cultures by using singular value decomposition

PROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 21 2007
Jiri Vohradsky Dr.
Abstract This paper describes a comparative systems level analysis of the developmental proteome and transcriptome in the model antibiotic-producing eubacterium Streptomyces coelicolor, cultured on different media. The analysis formulates expression as the superposition of effects of regulatory networks and biological processes which can be identified using singular value decomposition (SVD) of a data matrix formed by time series measurements of expression of individual genes throughout the cell cycle of the bacterium. SVD produces linearly orthogonal factors, each of which can represent an independent system behavior defined by a linear combination of the genes/proteins highly correlated with the corresponding factor. By using SVD of the developmental time series of gene expression, as measured by both protein and RNA levels, we show that on the highest level of control (representing the basic kinetic behavior of the population), the results are identical, regardless of the type of experiment or cultivation method. The results show that this approach is capable of identifying basic regulatory processes independent of the environment in which the organism lives. It also shows that these processes are manifested equally on protein and RNA levels. Biological interpretation of the correlation of the genes and proteins with significant eigenprofiles (representing the highest level kinetic behavior of protein and/or RNA synthesis) revealed their association with metabolic processes, stress responses, starvation, and secondary metabolite production. [source]


Influence of nonspecific brain and plasma binding on CNS exposure: implications for rational drug discovery

BIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 8 2002
J. Cory Kalvass
Abstract Relative plasma, brain and cerebrospinal fluid (CSF) exposures and unbound fractions in plasma and brain were examined for 18 proprietary compounds in rats. The relationship between in vivo brain-to-plasma ratio and in vitro plasma-to-brain unbound fraction (fu) was examined. In addition, plasma fu and brain fu were examined for their relationship to in vivo CSF-to-plasma and CSF-to-brain ratios, respectively. Findings were delineated based on the presence or absence of active efflux. Finally, the same comparisons were examined in FVB vs. MDR 1a/1b knockout mice for a selected P-glycoprotein (Pgp) substrate. For the nine compounds without indications of active efflux, predictive correlations were observed between ratios of brain-to-plasma exposure and plasma-to-brain fu (r2 = 0.98), CSF-to-brain exposure vs. brain fu (r2 = 0.72), and CSF-to-plasma exposure vs. plasma fu (r2 = 0.82). For the nine compounds with indications of active efflux, nonspecific binding data tended to over predict the brain-to-plasma and CSF-to-plasma exposure ratios. Interestingly, CSF-to-brain exposure ratio was consistently under predicted by brain fu for this set. Using a select Pgp substrate, it was demonstrated that the brain-to-plasma exposure ratio was identical to that predicted by plasma-to-brain fu ratio in MDR 1a/1b knockout mice. In FVB mice, plasma-to-brain fu over predicted brain-to-plasma exposure ratio to the same degree as the difference in brain-to-plasma exposure ratio between MDR 1a/1b and FVB mice. Consistent results were obtained in rats, suggesting a similar kinetic behavior between species. These data illustrate how an understanding of relative tissue binding (plasma, brain) can allow for a quantitative examination of active processes that determine CNS exposure. The general applicability of this approach offers advantages over species- and mechanism-specific approaches. Copyright © 2002 John Wiley & Sons, Ltd. [source]


Comparison of nitrophenylethyl and hydroxyphenacyl caging groups

BIOPOLYMERS, Issue 3 2001
Xinlin Du
Abstract Nitrophenylethyl (NPE)- and hydroxyphenacyl (HPA)-caged nucleotides were employed in a time-resolved Fourier transform IR spectroscopy study on Ras-catalyzed guanosine triphosphate (GTP) hydrolysis. A fast kinetic component was observed following the photolysis of NPE-caged nucleotides in the NPE-GTP-Ras complex. However, this kinetic component was not observed in the HPA-GTP-Ras experiment. This fast kinetic component was likely due to a chemical reaction between Ras and the detached caging group, nitrosoacetophenone. This communication serves as a note of caution in interpreting spectral changes and kinetic behavior of the enzymatic systems employing NPE-caged compounds. © 2001 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 62: 147,149, 2001 [source]


Kinetic responses of Dunaliella in moving fluids

BIOTECHNOLOGY & BIOENGINEERING, Issue 1 2010
Ahammed Anwar Chengala
Abstract The objective of this work was to quantify the kinetic behavior of Dunaliella primolecta (D. primolecta) subjected to controlled fluid flow under laboratory conditions. In situ velocities of D. primolecta were quantified by micron-resolution particle image velocimetry and particle tracking velocimetry. Experiments were performed under a range of velocity gradients and corresponding energy dissipation levels at microscopic scales similar to the energy dissipation levels of natural aquatic ecosystems. An average swimming velocity of D. primolecta in a stagnant fluid was 41,µm/s without a preferential flow direction. In a moving fluid, the sample population velocities of D. primolecta follow a log-normal distribution. The variability of sample population velocities was maximal at the highest fluid flow velocity in the channel. Local fluid velocity gradients inhibited the accrual of D. primolecta by twofold 5 days after the initiation of the experiment in comparison to the non-moving fluid control experiment. Biotechnol. Bioeng. 2010;107: 65,75. © 2010 Wiley Periodicals, Inc. [source]


Investigating pH and Cu (II) effects on lipase activity and enantioselectivity via kinetic and spectroscopic methods

BIOTECHNOLOGY JOURNAL, Issue 11 2006
Tian-Wen Xu
Abstract For Candida rugosa lipase (CRL) catalyzed hydrolysis of racemic 1-phenethyl acetate, both the weakly acidic pH (pH 6.0) and the addition of 1 mM copper (II) ion enhanced the enzyme activity and enantioselectivity (E value) about twofold, as compared with that under neutral pH and noadditive conditions. The decrease of activation free energy (,G) and increase of kcat(R)/kcat(S) at weakly acidic pH and/or in the presence of copper (II) characterized the kinetic behavior of CRL. On the other hand, for providing reasonable insights into the catalytic mechanism and the structural basis for enantioselectivity alteration, spectroscopic techniques were employed to probe conformational changes of the enzyme in each medium assayed. The fluorescence emission spectra revealed that pH and copper (II) might exert different effects on the microenvironment of Trp residue and thereby on the protein conformation, which could be further verified by UV-visible and Raman spectra. The conformational modulation of CRL associated with either pH or copper (II) concentration in the reaction medium could be attributed to the flexible and sensitive conformation of the enzyme, which is responsible for the significant variation of apparent activity and enantioselectivity with the tuning of biocatalyst microenvironment. [source]


Influence of water-miscible organic solvents on kinetics and enantioselectivity of the (R,-specific alcohol dehydrogenase from Lactobacillus brevis

BIOTECHNOLOGY JOURNAL, Issue 5 2006
Jan Schumacher
Abstract Using the organic solvents acetonitrile and 1,4-dioxane as water-miscible additives for the alcohol dehydrogenase (ADH)-catalyzed reduction of butan-2-one, we investigated the influence of the solvents on enzyme reaction behavior and enantioselectivity. The NADP+ -dependent (R,-selective ADH from Lactobacillus brevis (ADH-LB) was chosen as biocatalyst. For cofactor regeneration, the substrate-coupled approach using propan-2-ol as co-substrate was applied. Acetonitrile and 1,4-dioxane were tested from mole fraction 0.015 up to 0.1. Initial rate experiments revealed a complex kinetic behavior with enzyme activation caused by the substrate butan-2-one, and increasing KM values with increasing solvent concentration. Furthermore, these experiments showed an enhancement of the enantioselectivity for (R,-butan-2-ol from 37% enantiomeric excess (ee) in pure phosphate buffer up to 43% ee in the presence of 0.1 mol fraction acetonitrile. Finally, the influence of the co-solvents on water activity of the reaction mixture and on enzyme stability was investigated. [source]


Spectral kinetic modeling and long-term behavior assessment of Arthrospira platensis growth in photobioreactor under red (620 nm) light illumination

BIOTECHNOLOGY PROGRESS, Issue 1 2009
Bérangčre Farges
Abstract The ability to cultivate the cyanobacterium Arhtrospira platensis in artificially lightened photobioreactors using high energetic efficiency (quasi-monochromatic) red LED was investigated. To reach the same maximal productivities as with the polychromatic lightening control conditions (red + blue, P/2e, = 1.275), the need to work with an optimal range of wavelength around 620 nm was first established on batch and continuous cultures. The long-term physiological and kinetic behavior was then verified in a continuous photobioreactor illuminated only with red (620 nm) LED, showing that the maximum productivities can be maintained over 30 residence times with only minor changes in the pigment content of the cells corresponding to a well-known adaptation mechanism of the photosystems, but without any effect on growth and stoichiometry. For both poly and monochromatic incident light inputs, a predictive spectral knowledge model was proposed and validated for the first time, allowing the calculation of the kinetics and stoichiometry observed in any photobioreactor cultivating A. platensis, or other cyanobacteria if the parameters were updated. It is shown that the photon flux (with a specified wavelength) must be used instead of light energy flux as a relevant control variable for the growth. The experimental and theoretical results obtained in this study demonstrate that it is possible to save the energy consumed by the lightening device of photobioreactors using red LED, the spectral range of which is defined according to the action spectrum of photosynthesis. This appears to be crucial information for applications in which the energy must be rationalized, as it is the case for life support systems in closed environments like a permanent spatial base or a submarine. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source]


KINETICS OF SOYBEAN LIPOXYGENASES ARE RELATED TO pH, SUBSTRATE AVAILABILITY AND EXTRACTION PROCEDURES

JOURNAL OF FOOD BIOCHEMISTRY, Issue 2 2008
VERONICA S. CHEDEA
ABSTRACT The kinetic patterns of pure soy lipoxygenase LOX-1 and crude or defatted soybean extracts containing LOX isoenzymes (LOX-1, LOX-2 and LOX-3) were studied by UV spectrometry at 234 and 280 nm, depending on their extraction and measurement conditions. Different pHs (from 6.0 to 9.0), corresponding to specific activation of LOX isoenzymes and the ratios of enzyme protein per substrate were used in order to evaluate the enzyme rates, as indicators of its affinity for substrate in different environments. The crude soy extract contained mainly LOX-1 activity (measured at 234 nm, at pH 9.0) and LOX-3, in an approximate ratio of 3:1. The LOX-2 activity was very low. The defatted extracts buffered at pH 6.8 and 7.1 showed a low LOX-1 and LOX 2 activity, but mostly LOX-3 activity (measured at 280 nm, at pH 7.1), with a mirror-type relation between the enzyme/substrate ratio and their enzymatic specific activity. The results suggest that defatting inhibits specifically the LOX-1 activity and indicate the possibility to modulate LOX activity by modifications of enzyme/substrate ratios and modifications of pH in the enzyme environment. PRACTICAL APPLICATIONS Because of the specific kinetic behaviors of the three different LOXs found in crude soy extracts involved in off-flavor generation, one can modulate the inhibition of these isoenzymes during soybean processing. Our experiments showed that pH variation could be a simple solution to inhibit the LOX isoenzymes, and therefore, the off-flavor generation. From the analytical point of view, the techniques described in this article are designed to be as simple as possible, and easy to use at large-scale level in food industry (food chain control). The idea is to minimize the number of separate chemical manipulations and, thereby, minimize errors. These studies can offer the background of further inhibition experiments in vitro using natural extracts. The LOX inhibition by natural antioxidants is related as well to pH and other factors influencing the enzyme's activity; this idea can be also valorized practically in the future. [source]


THERMAL INACTIVATION KINETICS OF ALKALINE PHOSPHATASE IN BUFFER AND MILK

JOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 3 2006
S. FADILO
ABSTRACT A detailed kinetic study on the thermal inactivation of alkaline phosphatase (ALP) added into buffer and pasteurized milk and for ALP naturally present in raw cow's milk has been performed. Kinetic parameters (rate constant, k; decimal reduction time, D; activation energy, Ea; and z value) were evaluated based on the first-order rate model at 50,80C. The temperature sensitivity of the kinetic parameters was evaluated considering the Arrhenius-type Ea model. All kinetic behaviors were well described by the first-order model (r2 > 0.91). The D values increased with increasing temperature. Higher temperatures resulted in higher rates of enzyme inactivation as indicated by lower D values and higher k values. There are significant differences (P < 0.01) among the D values for ALP in buffer and milk at treated temperatures. The rate of enzyme inactivation was much more rapid in buffer than in pasteurized milk. The evaluated Ea values for ALP added into the buffer and pasteurized milk, and for ALP naturally present in raw milk were 97.2, 149.9 and 207.8 kJ/mol, respectively. The inactivation kinetics of ALP during heat treatment was found to be dependent on the composition of the medium, and the time and temperature of the heat treatment. [source]