Energy Of Deactivation Research Articles

Catalytic properties of the immobilized Aspergillus tamarii xylanase

Xylanase from Aspergillus tamarii was covalently immobilized on Duolite A147 pretreated with the bifunctional agent glutaraldehyde. The bound enzyme retained 54.2% of the original specific activity exhibited by the free enzyme (120 U/mg protein). Compared to the free enzyme, the immobilized enzyme exhibited lower optimum pH, higher optimum reaction temperature, lower energy of activation, higher Km (Michaelis constant), lower Vmax (maximal reaction rate). The half-life for the free enzyme was 186.0, 93.0, and 50.0 min for 40, 50, and 60 degrees C, respectively, whereas the immobilized form at the same temperatures had half-life of 320, 136, and 65 min. The deactivation rate constant at 60 degrees C for the immobilized enzyme is about 6.0 x 10(-3), which is lower than that of the free enzyme (7.77 x 10(-3) min). The energy of thermal deactivation was 15.22 and 20.72 kcal/mol, respectively for the free and immobilized enzyme, confirming stabilization by immobilization. An external mass transfer resistance was identified with the immobilization carrier (Duolite A147). The effect of some metal ions on the activity of the free and immobilized xylanase has been investigated. The immobilized enzyme retained about 73.0% of the initial catalytic activity even after being used 8 cycles.

Characterization of cyclodextrin glycosyltransferase from Bacillus firmus strain no. 37.

The enzyme cyclodextrin glycosyltransferase (CGTase), EC 2.4.1.19, which produces cyclodextrins (CDs) from starch, was obtained from Bacillusfirmus strain no. 37 isolated from Brazilian soil and characterized in the soluble form using as substrate 100 g/L of maltodextrin in 0.05 M Tris-HCl buffer, 5 mM CaCl2, and appropriate buffers. Enzymatic activity and its activation energy were determined as a function of temperature and pH. The activation energy for the production of beta- and gamma-CD was 7.5 and 9.9 kcal/mol, respectively. The energy of deactivation was 39 kcal/mol. The enzyme showed little thermal deactivation in the temperature range of 35-60 degrees C, and Arrhenius-type equations were obtained for calculating the activity, deactivation, and half-life as a function of temperature. The molecular weight of the enzyme was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis, giving 77.6 kDa. Results for CGTase activity as a function of temperature gave maximal activity for the production of beta-CD at 65 degrees C, pH 6.0, and 71.5 mmol of beta-CD/(min x mg of protein), whereas for gamma-CD it was 9.1 mmol of gamma-CD/(min mg of protein) at 70 degrees C and pH 8.0. For long contact times, the best use of the enzymatic activity occurs at 60 degrees C or at a lower temperature, and the reaction pH may be selected to increase the yield of a desired CD.

Thermal stability and energy of deactivation of free and immobilized cellobiase

Commercial cellobiase has been immobilized in controlled pore silica particles by covalent binding with the silane-glutaraldehyde method with protein and activity yields of 67% and 13.7%, respectively. Thermal stability of the free and immobilized enzyme (IE) was determined with 0.2% w/v cellobiose solution, pH 4.8, temperatures from 40 to 70°C for free enzyme and 40 to 75°C for IE. Free cellobiase maintained its activity practically constant for 240 min at temperatures up to 55°C. The IE has shown higher stability retaining its activity in the same test up to 60° C. Half-lives for free enzyme were 14.1, 2.1 and 0.17 h at 60, 65 and 70°C, respectively, whereas the IE at the same temperatures had half-lives of 245, 21.3 and 2.9 h. The energy of thermal deactivation was 80.6 kcal/mol for the free enzyme and 85.2 kcal/mol for the IE, confirming stabilization by immobilization.

Thermal stability and deactivation energy of free and immobilized invertase

The thermal stability and the energy of deactivation of free invertase and the immobilized enzyme (IE) was measured at temperatures in the range of 35 to 65°C for the hydrolysis of a 5% w/v sucrose solution. The free enzyme at pH 5.0 is stable up to 50°C for a period of 4 h. Invertase immobilized in controlled pore silica by the silane-glutaraldehyde covalent method is stable up to 55oC, in pH 4.5 for the same period. For higher temperatures the enzyme deactivation follows the exponential decay model and half-lives are 0.53, 1.80, and 13.9 h for free invertase, at 65, 60, and 55oC, respectively. For the IE half-lives are 0.48, 1.83, and 20.9 h, at 65, 60, and 55oC, respectively. The IE is more stable than the free invertase; the energy of deactivation being 83.1 kcal/mol for the IE and 72.0 kcal/mol for the free enzyme.

Modeling cellobiose hydrolysis with integrated kinetic models.

The enzyme cellobiase Novozym 188, which is used for improving hydrolysis of bagasse with cellulase, was characterized in its commercial available form and integrated kinetic models were applied to the hydrolysis of cellobiose. The specific activity of this enzyme was determined for pH values from 3.0-7.0, and temperatures from 40-75 degrees C, with cellobiose at 2 g/L. Thermal stability was measured at pH 4.8 and temperatures from 40-70 degrees C. Substrate inhibition was studied at the same pH, 50 degrees C, and cellobiose concentrations from 0.4-20 g/L. Product inhibition was determined at 50 degrees C, pH 4.8, cellobiose concentrations of 2 and 20 g/L, and initial glucose concentration nearly zero or 1.8 g/L. The enzyme has shown the greatest specific activity, 17.8 U/mg, at pH 4.5 and 65 degrees C. Thermal activation of the enzyme followed Arrhenius equation with the Energy of Activation being equal to 11 kcal/mol for pH values 4 and 5. Thermal deactivation was adequately modeled by the exponential decay model with Energy of Deactivation giving 81.6 kcal/mol. Kinetics parameters for substrate uncompetitive inhibition were: Km = 2.42 mM, Vmax = 16.31 U/mg, Ks = 54.2 mM. Substrate inhibition was clearly observed above 10 mM cellobiose. Product inhibition at the concentration studied has usually doubled the time necessary to reach the same conversion at the lower temperature tested.

Thermal stability and energy of deactivation of free and immobilized amyloglucosidase in the saccharification of liquefied cassava starch.

Amyloglucosidase from Novo (Copenhagen, Denmark) was immobilized in controlled pore silica particles with the silane-glutaraldehyde covalent method. Thermal stability of the free and immobilized enzyme (IE) was determined with 30% (w/v) alpha-amylase liquefied cassava starch, pH 4.5, temperatures from 35 to 75 degrees C. Free amyloglucosidase maintained its activity practically constant for 240 min and temperatures up to 50 degree C. The IE has shown higher stability retaining its activity for the same period up to 60 degrees C. Half-life for free enzyme was 20.6, 6.44, 2.07, 0.69, and 0.24 h for 55, 60, 65, 70, and 75 degrees C, respectively, whereas the IE at the same temperatures had half-lives of 116.4, 30.88, 8.52, 2.44, and 0.73 h. The energy of thermal deactivation was thus 50.6 and 57.6 kcal/mol, respectively for the free and IE, confirming stabilization by immobilization.

PH and thermal stability studies of chitinase from Trichoderma harzianum: A thermodynamic consideration

The combined effect of pH and temperature on chitinase was investigated using response surface methodology. A central composite design for two variables was employed. The optimal pH and temperature for the least degree of deactivation were found out to be 5.4 and 24°C respectively. The deactivation rate constants and the half life of chitinase were estimated at different pH and temperature combinations. At the optimal pH of 5.4, the rate of the deactivation was found to be the least. Thermodynamic parameters, viz., ΔH*, ΔS*, ΔG* and activation energy of thermal deactivation of chitinase were calculated in the temperature range from 50°C to 60°C.

Relative in Vivo Activity and Simulated Sunlight-uv Stability of Inclusion Bodies od a Wild-Type and an Engineered Polyhedral Envelope-Negative Isolate of the Nucleopolyhedrosis Virus of Autographa californica

Virus stability and infectivity during stressful conditions was assessed to establish guidelines for future virus filtration experiments and to contribute to the body of knowledge on a widely used virus. A recombinant baculovirus of Autographa californica M nucleopolyhedrovirus (AcMNPV), vHSGFP, was incubated at 15–65 °C. A 2-log decrease in virus infectivity occurred after virus incubation above 45 °C. The activation energy of virus deactivation was circa 108 kJ/mol. Dynamic light scattering revealed an increase in apparent virus particle size from 150 ± 19 to 249 ± 13 nm at 55 °C. Protein and DNA concentrations in solution correlated well with virus aggregation as temperature was increased. Infectivity of vHSGFP stored for 5 months at 4 °C or exposed to shear stress from stirring (100 rpm, 1.02 × 10−5 psi) and pumping (50–250 ml/min, 1.45 × 10−5 to 7.25 × 10−5 psi) did not change with time. Unlike temperature variations, cold storage and shear stress appeared to have little impact on infectivity.

Thermal deactivation kinetics of CM-cellulase from a local isolate of Aspergillus niger (RD-2231)

The kinetic of thermal deactivation of CMC-ase activity of A. niger, locally isolated, was studied. The enzyme was found to be more stable in temperatures below 40 degrees C. The rates of activity decay were significant at high temperatures and can be described as a first-order kinetic model. Deactivation rate constants (Kd) were determined at different temperatures (30, 40, 55 and 65 degrees C). Kd value for CMC-ase activity decay at 65 degrees C was 28 times higher than its value at 30 degrees C. An Arrhenius type temperature dependence of Kd was found, and the activation energy (Ea) of the thermal deactivation was calculated to be 8400 cal/mole. Thermodynamic quantities (delta H) and (delta S) for deactivation process were 7700 and 11.9 cal/mole, respectively. The change of two kinetic parameters, i.e. Vmax and Km under deactivation conditions, was discussed.

Graphical determination of mean activation energy and standard deviation in a microheterogeneity model of enzyme deactivation

Traditionally, enzyme populations have been treated as if they were either homogenous, or heterogeneous with distinct and separable subpopulations. The microheterogeneity model, however, assumes that there is a continuous distribution of properties in the population. In the area of enzyme deactivation kinetics, this model describes the heterogeneous population as having a continuous distribution of activation energy of deactivation. This distribution is characterized by mean activation energy, and a standard deviation of activation energy. The microheterogeneity model contains two parameters, (0) and sigma. Parameter (0) is the mean value of for a heterogeneous enzyme population; is the activation energy divided by absolute temperature and the ideal gas constant. Parameter sigma is the standard deviation of the Gaussian distribution of values in the population. If the population is homogeneous, then = (0) for all enzyme molecules and sigma = 0. There are certain ratios which are independent of (0) and dependent upon sigma. Two important ratios are t(1/4)/t(1/2) and t(1/2)/t(1/2) ('), where t(1/2) (') represents t(1/2) for a homogeneous enzyme population with the same mean ((0)), as the heterogeneous population. If there is experimental deactivation data for the heterogeneous population which is well behaved, the first ratio, t(1/4)/t(1/2), can be determined by estimating the time in minutes at which the enzyme has lost 25% of its activity (t(1/4)), and the time in minutes at which the enzyme has lost 50% of its activity (t(1/2)), and then taking the ratio t(1/4)/t(1/2). The corresponding value of sigma can be estimated from a graph. The ratio t(1/2)/t(1/2) (') can be found directly as a function of t(1/4)/t(1/2), and can be estimated from another graph. The value of (0) can then be calculated from the formulas given in the article.

The kinetics of the thermal deactivation of transglutaminase from guinea‐pig liver

By incubating native (N) transglutaminase from guinea-pig liver at various temperatures and assaying it at 25 degrees C, two steps in the irreversible deactivation process to the denatured form (D) have been found. The fitting of the data to the equations of two possible models (the two-steps model and the two-isoenzymes model) is only compatible with the first one (N----X----D). It is shown that the structure of the active intermediate, X, depends on the deactivation temperature and on the thermal history of the enzyme. This may mean that transglutaminase exists in a large number of microstates. Surprisingly, the activation energy of deactivation is lower than that of activity (36.6 +/- 3.4 against 47.2 +/- 2.2 kJ.mol-1). By deactivating transglutaminase at a constant temperature (55 degrees C) and assaying it at variable temperatures, the activation energy of the intermediate, (X55), has been determined to be 40.2 +/- 5 kJ.mol-1, of the same order of magnitude as the native form. Among several agents assayed, only Ca2+ had a positive effect on the thermal stability of this enzyme. At 40 degrees C, transglutaminase was quite stable in the presence of Ca2+ (in its absence, the half-life was 65 min) and at 45 degrees C, its thermostability had been considerably increased, the half-life being raised from 47 min to 275 min.

Variation with time of the mechanism, observable order, and activation energy of catalyst deactivation by coke in the FCC process

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTVariation with time of the mechanism, observable order, and activation energy of catalyst deactivation by coke in the FCC processJose Corella, Rafael Bilbao, Jose A. Molina, and Alfonso ArtigasCite this: Ind. Eng. Chem. Process Des. Dev. 1985, 24, 3, 625–636Publication Date (Print):July 1, 1985Publication History Published online1 May 2002Published inissue 1 July 1985https://doi.org/10.1021/i200030a018RIGHTS & PERMISSIONSArticle Views236Altmetric-Citations42LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts

Metastable Activation in Rapid Thermal Annealed Arsenic Implanted Silicon

ABSTRACTLow temperature (600–800&C) thermal treatment subsequent to high temperature short time anneal of As implanted Si has resulted in significant clustering of As atoms in Si. Si wafers implanted with As at a variety of doses and energies were subjected to single and multiple thermal anneals using incoherent tungsten radiation. Sheet resistance (R▩ ), and Rutherford backscattering (RBS) and channeling measurements were carried out on the wafers. The metastable behavior observed in the activation of As was attributed to electrical deactivation of As atoms caused by clustering. From the temperature dependence of the rate of increase in R▩ we extracted a value of 1.1 eV for the activation energy of electronic deactivation of As atoms in agreement with the value obtained earlier for the activation of As clustering. We also report, for the first time, observation of a structure in the Si RBS spectrum which represents a defective layer in Si caused by the clustering As atoms.

Optimal temperature operation for hydrolysis of sucrose by immobilized invertase.

Taking the hydrolysis of sucrose by invertase as an example, optimal temperature operation (OTO) for the batchwise immobilized enzymatic reaction accompanied by first-order enzyme deactivation was studied. From a comparison with isothermal operation (ITO), the following results were obtained. 1) Both in OTO and in ITO, ξ (=ratio of the activation energy of deactivation to that of reaction) is the most important parameter for operational design concerning the effective use of immobilized enzyme. The larger the value of ξ, the more the enzyme can be utilized repeatedly to result in higher conversion. 2) It was found theoretically and experimentally that OTO gives higher final conversion, Xf, at given βf (final residual enzymatic activity) and tf (total reaction time) than ITO. 3) In OTO, a parameter βf, exp, the advisable minimum enzymatic activity at the final stage of the operation, is a useful measure for the design of optimal temperature operation.

Polar substituents and the luminescence of organic compounds

An hypothesis is presented in which the interaction of inductive effects on the π-electron system of a complex molecule is interpreted as a shift in the potential energy of the ground and excited states. The model allows the effect of polar substituents on various luminescence processes to be described. It is predicted that the rate constant and the activation energy of radiationless deactivation of the first excited singlet state, as well as the energy of the O–O phosphorescence band, will be correlated by Taft σ* substituent constants.