Continuous production of monoacylglycerol via glycerolysis of babassu oil by immobilized Burkholderia cepacia lipase in a packed bed reactor.

This study investigated the glycerolysis of babassu oil by Burkholderia cepacia lipase immobilized on SiO2-PVA particles in a continuous packed bed reactor. Experiments were conducted in a solvent-free system at 273.15 K either in an inert atmosphere or in the presence of cocoa butter to prevent lipid oxidation. The reactor (15 × 55 mm) was run at a fixed space time of 9.8 h using different molar ratios of babassu oil to glycerol (1:3, 1:6, 1:9, 1:12, and 1:15) to assess the effects of reactant molar ratio on monoacylglycerol productivity and selectivity. Nitrogen atmosphere and cocoa butter were equally effective in inhibiting lipid oxidation, indicating that addition of cocoa butter to glycerolysis reactions may be an interesting cost-reduction strategy. An oil/glycerol molar ratio of 1:9 resulted in the highest productivity (52.3 ± 2.9 mg g-1 h-1) and selectivity (31.5 ± 1.8%). Residence time distribution data were fitted to an axial dispersion model for closed-vessel boundary conditions, giving a mass transfer coefficient (kc) of 3.4229 × 10-6 m s-1. A kinetic model based on elementary steps of the studied reaction was written in Scilab and compared with experimental data, providing standard deviations in the range of 5.5-7.5%.

Computational and experimental analysis on the preferential selectivity of lipases for triglycerides in Licuri oil.

In the present study, we demonstrated the use of molecular docking as an efficient in silico screening tool for lipase-triglyceride interactions. Computational simulations using the crystal structures from Burkholderia cepacia lipase (BCL), Thermomyces lanuginosus lipase (TLL), and pancreatic porcine lipase (PPL) were performed to elucidate the catalytic behavior with the majority triglycerides present in Licuri oil, as follows: caprilyl-dilauryl-glycerol (CyLaLa), capryl-dilauryl-glycerol (CaLaLa), capryl-lauryl-myristoyl-glycerol (CaLaM), and dilauryl-myristoyl-glycerol (LaLaM). The computational simulation results showed that BCL has the potential to preferentially catalyze the major triglycerides present in Licuri oil, demonstrating that CyLaLa, (≈25.75% oil composition) interacts directly with two of the three amino acid residues in its catalytic triad (Ser87 and His286) with the lowest energy (-5.9 kcal/mol), while other triglycerides (CaLaLa, CaLaM, and LaLaM) interact with only one amino acid (His286). In one hard, TLL showed a preference for catalyzing the triglyceride CaLaLa also interacting with His286 residue, but, achieving higher binding energies (-5.3 kcal/mol) than found in BCL (-5.7 kcal/mol). On the other hand, PPL prefers to catalyze only with LaLaM triglyceride by His264 residue interaction. When comparing the computational simulations with the experimental results, it was possible to understand how BCL and TLL display more stable binding with the majority triglycerides present in the Licuri oil, achieving conversions of 50.86 and 49.01%, respectively. These results indicate the production of fatty acid concentrates from Licuri oil with high lauric acid content. Meanwhile, this study also demonstrates the application of molecular docking as an important tool for lipase screening to reach a more sustainable production of fatty acid concentrates from vegetable oils.

"Recent advances on support materials for lipase immobilization and applicability as biocatalysts in inhibitors screening methods"-A review.

With a substantial demand for new anti-obesity drugs for the treatment of obesity, screening lipase inhibitors from natural products has become a popular approach toward drug discovery. Due to the significant advantages of excellent reusability, stability and endurance in extreme pH and temperature conditions, lipase immobilization has been employed as a promising strategy to screen lipase inhibitors. Support is a key factor in the process of enzyme immobilization used to provide excellent biocompatibility, stable physical and chemical properties and abundant binding sites for enzymes. Thus, various supports, including nanofibers, polymeric monoliths, mesoporous materials, nanomaterials, membrane and cellulose paper, are systematically introduced and discussed in this review. Considering these supports, the application of the immobilization of lipase in screening compounds from natural products is also comprehensively reviewed, and the outlook for future research directions is described.

Amano Lipase PS-catalyzed Hydrolysis of Pine Nut Oil for the Fatty Acids Production Using Deep Eutectic Solvent as Co-solvent.

Free fatty acids (FFAs) are the important material used in food, personal care, emulsifiers, adhesives and surfactants. In order to enhance the preparation of FFAs, the effects of reaction variables, optimization, thermodynamic property for the Amano lipase PS catalyzed hydrolysis of pine nut oil (PNO) using deep eutectic solvents (DESs) as co-solvents were studied. The results showed that FFAs could be successfully prepared from pine nut oil through Amano lipase PS catalyzed hydrolysis using Choline chloride:Urea (ChCl:U, 1:2, mol/mol) as co-solvent. Under the optimal conditions (reaction temperature 46°C, water amount 38%, DES addition 43%, lipase dosage 7.6%, reaction time 13 h), the maximum content of FFAs in the products and degree of hydrolysis (DH) of oil were up to 89.1 ± 1.9% and 92.7 ± 2.2%, respectively. The effects of reaction variables on the hydrolysis increased in the order of DES addition < reaction temperature < reaction time < lipase dosage < water amount. The thermodynamics (Arrhenius equation) for the triglycerides hydrolysis was V = 4289.39·exp(-22942.09/RT) with the activation energy (Ea) of 22.94 kJ/mol. The Gibbs free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) were 81.50 ± 2.64 kJ/mol, 20.18 ± 0.12 kJ/mol and -184.59 ± 0.36 J/mol/K, respectively. The lipase in the aqueous DES could be directly re-used for 3 times.

Scaled-up biodiesel synthesis from Chinese Tallow Kernel oil catalyzed by Burkholderia cepacia lipase through ultrasonic assisted technology: A non-edible and alternative source of bio energy.

In East Asia, for thousands of years, the fruit of Chinese tallow tree (Sapium sebiferum) has been used for multiple purposes because of its chemical composition; the presence of high amounts of lipids is remarkable, showing potential to be used as substrate for biodiesel synthesis. Previously have been reported the use of alkaline and enzymatic catalysts, microwave technology and the use of ionic liquids as co-solvents with the lipids of this tree species to produce biodiesel. This study shows the results of the use of Burkholderia cepacia lipase as enzymatic catalyst for transesterification of Chinese Tallow Kernel oil (CTK), extracted from the fruit of Chinese tallow tree, into biodiesel, with the use of ultrasonic assisted technology and without the usage of solvents. The optimal operational parameters were determined and the reactions were developed in a batch reactor with the use of ultrasonic irradiation and emulsification to enhance the mass transfer. The scaled-up experiments, in an especially designed 3 L capacity reactor, showed promising results, obtaining 55.20% biodiesel and a kinematic viscosity of 10.31 mm2.s-1 in only 4 h, in comparison with previously published (in vitro) methods. The valorization of this non-edible source of oil represents an opportunity to use as an alternative source for bioenergy and also to tackle the uncontrolled expansion of this oleaginous tree species in some ecologically fragile ecosystems.

Lipase Immobilization on Silica Xerogel Treated with Protic Ionic Liquid and its Application in Biodiesel Production from Different Oils.

Treated silica xerogel with protic ionic liquid (PIL) and bifunctional agents (glutaraldehyde and epichlorohydrin) is a novel support strategy used in the effective immobilization of lipase from Burkholderia cepacia (LBC) by covalent binding. As biocatalysts with the highest activity recovery yields, LBC immobilized by covalent binding with epichlorohydrin without (203%) and with PIL (250%), was assessed by the following the hydrolysis reaction of olive oil and characterized biochemically (Michaelis⁻Menten constant, optimum pH and temperature, and operational stability). Further, the potential transesterification activity for three substrates: sunflower, soybean, and colza oils, was also determined, achieving a conversion of ethyl esters between 70 and 98%. The supports and the immobilized lipase systems were characterized using Fourier transform infrared spectra (FTIR), scanning electron microscopy (SEM), elemental analysis, and thermogravimetric (TG) analysis.

Burkholderia cepacia lipase immobilized on heterofunctional magnetic nanoparticles and its application in biodiesel synthesis.

Biodiesel production using immobilized lipase as a biocatalyst is a promising process. The performance of immobilized lipase is mainly determined by supporting materials and immobilization method. To avoid the shortcomings of adsorption and covalent bonding methods, in this study, we developed a novel heterofunctional carrier of being strengthened anion exchange and weakened covalent binding to avoid activity loss and improve operational stability of the immobilized lipase. 2,3-epoxypropyltrimethylammonium chloride with epoxy and quaternary ammonium group and glutaraldehyde were grafted onto aminated magnetic nanoparticles (AMNPs) to generate a new matrix, named GEAMNP. Then Burkholderia cepacia lipase (BCL) was immobilized on GEAMNP via anion exchange and covalent bonding. The transesterification between soybean oil and methanol was used to test the activities. Activity recovery of the immobilized BCL was up to 147.4% and the corresponding transesterification activity was 1.5-fold than that of BCL powder. The immobilized lipase was further used for biodiesel production to confirm its feasibility. The fatty acid methyl esters conversion yield could reach 96.8% in the first 12 h. Furthermore, the immobilized lipase, BCL-GEAMNP showed markedly improved operational stability, better reusability and higher esters than BCL-GAMNP, where MNPs were only modified with (3-aminopropyl) triethoxysilane and glutaraldehyde.

Enzymatic transesterification of waste vegetable oil to produce biodiesel.

An experimental study on enzymatic transesterification was performed to produce biodiesel from waste vegetable oils. Lipase from Pseudomonas cepacia was covalently immobilized on a epoxy-acrylic resin support. The immobilized enzyme exhibited high catalytic specific surface and allowed an easy recovery, regeneration and reutilisation of biocatalyst. Waste vegetable oils - such as frying oils, considered not competitive with food applications and wastes to be treated - were used as a source of glycerides. Ethanol was used as a short chain alcohol and was added in three steps with the aim to reduce its inhibitory effect on lipase activity. The effect of biocatalyst/substrate feed mass ratios and the waste oil quality have been investigated in order to estimate the process performances. Biocatalyst recovery and reuse have been also studied with the aim to verify the stability of the biocatalyst for its application in industrial scale.

Effect of natural antioxidants on the lipase activity in the course of batch and continuous glycerolysis of babassu oil.

The effects of several natural antioxidants (copaiba oil, buriti oil, cocoa butter, tucuman butter, oregano and white thyme) were assessed in the enzymatic synthesis of monoglycerides (MAG) from the glycerolysis of babassu oil. The reactions were catalyzed by Burkholderia cepacia lipase immobilized on SiO2-PVA and the assays carried out in batch and continuous runs. Results were compared with those attained in the control reactions (without any strategy to avoid oxidation), and the best approach was tested in a continuous packed-bed reactor. The best performance was obtained using N2 in the reaction medium (60 % of MAG) followed by buriti oil (57.6 % of MAG) and cocoa butter (56.6 % of MAG), preventing the oxidation of babassu oil in batch reaction. However, the incorporation of buriti oil in the medium influenced the MAG profile, leading to the largest formation of monoolein, unlike other runs. Similar results were obtained in continuous reactions, using inert atmosphere and cocoa butter (24-25 % of MAG). Thereby, among the tested antioxidant agents, cocoa butter was the most effective in both systems, because it did not interfere in the MAG profile and also reduced the cost of the process.

Biodiesel production from Jatropha oil catalyzed by immobilized Burkholderia cepacia lipase on modified attapulgite.

Lipase from Burkholderia cepacia was immobilized on modified attapulgite by cross-linking reaction for biodiesel production with jatropha oil as feedstock. Effects of various factors on biodiesel production were studied by single-factor experiment. Results indicated that the best conditions for biodiesel preparation were: 10 g jatropha oil, 2.4 g methanol (molar ratio of oil to methanol is 1:6.6) being added at 3h intervals, 7 wt% water, 10 wt% immobilized lipase, temperature 35°C, and time 24h. Under these conditions, the maximum biodiesel yield reached 94%. The immobilized lipase retained 95% of its relative activity during the ten repeated batch reactions. The half-life time of the immobilized lipase is 731 h. Kinetics was studied and the Vmax of the immobilized lipases were 6.823 mmol L(-1). This immobilized lipase catalyzed process has potential industrial use for biodiesel production to replace chemical-catalyzed method.

Incorporation of omega-3 polyunsaturated fatty acids into soybean lecithin: effect of amines and divalent cations on transesterification by lipases.

The transesterification of soybean lecithin with methyl esters of EPA and DHA in an organic solvent (hexane) using various commercially available lipases was studied. Lipases produced by Candida antarctica, Pseudomonas fluorescens, Burkholderia cepacia, Mucor miehei, Thermomyces lanuginosus and Rhizomucor miehei were compared, in the absence or presence of histidine, arginine, urea, Ca²âº, Mg²âº, or a combination of urea and divalent cations (additives at 5 % of the total lipid mass). Transesterification using the R. miehei enzyme reached 11.32 and 12.30 % in the presence of Ca²âº or Mg²âº respectively, and 8.58 and 9.31 % when urea was also added. These were the greatest degrees of transesterification obtained. The results suggest the potential use of this immobilized lipase as a catalyst for interesterification reactions in organic solvent systems with low water content.

Protic ionic liquid as additive on lipase immobilization using silica sol-gel.

Ionic liquids (ILs) have evolved as a new type of non-aqueous solvents for biocatalysis, mainly due to their unique and tunable physical properties. A number of recent review papers have described a variety of enzymatic reactions conducted in IL solutions, on the other hand, to improve the enzyme's activity and stability in ILs; major methods being explored include the enzyme immobilization (on solid support, sol-gel, etc.), protic ionic liquids used as an additive process. The immobilization of the lipase from Burkholderia cepacia by the sol-gel technique using protic ionic liquids (PIL) as additives to protect against inactivation of the lipase due to release of alcohol and shrinkage of the gel during the sol-gel process was investigated in this study. The influence of various factors such as the length of the alkyl chain of protic ionic liquids (monoethanolamine-based) and a concentration range between 0.5 and 3.0% (w/v) were evaluated. The resulting hydrophobic matrices and immobilized lipases were characterised with regard to specific surface area, adsorption-desorption isotherms, pore volume (V(p)) and size (d(p)) according to nitrogen adsorption and scanning electron microscopy (SEM), physico-chemical properties (thermogravimetric - TG, differential scanning calorimetry - DSC and Fourier transform infrared spectroscopy - FTIR) and the potential for ethyl ester and emulsifier production. The total activity yields (Y(a)) for matrices of immobilized lipase employing protic ionic liquids as additives always resulted in higher values compared with the sample absent the protic ionic liquids, which represents 35-fold increase in recovery of enzymatic activity using the more hydrophobic protic ionic liquids. Compared with arrays of the immobilized biocatalyst without additive, in general, the immobilized biocatalyst in the presence of protic ionic liquids showed increased values of surface area (143-245 m(2) g(-1)) and pore size (19-38 Å). Immobilization with protic ionic liquids also favoured reduced mass loss according to TG curves (always less than 42.9%) when compared to the immobilized matrix without protic ionic liquids (45.1%), except for the sample containing 3.0% protic ionic liquids (46.5%), verified by thermogravimetric analysis. Ionic liquids containing a more hydrophobic alkyl group in the cationic moiety were beneficial for recovery of the activity of the immobilized lipase. The physico-chemical characterization confirmed the presence of the enzyme and its immobilized derivatives obtained in this study by identifying the presence of amino groups, and profiling enthalpy changes of mass loss.

Packed-bed reactor running on babassu oil and glycerol to produce monoglycerides by enzymatic route using immobilized Burkholderia cepacia lipase.

The aim of this study was the glycerolysis of babassu oil catalyzed by immobilized lipase from Burkholderia cepacia, in a continuous packed-bed reactor. The best reaction conditions were previously established in batchwise via response surface methodology as a function of glycerol-to-oil molar ratio and reaction temperature. The reactor operated continuously for 22 days at 50 degrees C, and during the first 6 days, no significant decrease on the initial lipase activity was observed. Monoglycerides concentration was in the range from 25 to 33 wt.%. Subsequently, a progressive decrease in the activity was detected, and an inactivation profile described by Arrhenius model estimated values of 50 days and 1.37 x 10(-2) h(-1) the half-life and deactivation coefficient, respectively.

Expanded bed adsorption of an alkaline lipase from Pseudomona cepacia.

An extracellular lipase was isolated from Pseudomona cepacia by expanded bed adsorption on an Amberlite 410 ion-exchange resin. Enzyme characterization and hydrodynamic study of a chromatography column were done. Enzyme purification was done at three condition of expanded bed height (H): at one and half (6cm), at two (8cm) and at three (12cm) times the fixed bed height (H(0)=4cm). The results showed that the experimental data was fitted to the Richardson and Zaki equation, and the comparison between the experimental and calculated terminal velocities showed low relative error. In enzyme purification for better condition, a purification factor of about 80 times was found at 6cm of expanded bed height, or 1.5 times of expansion degree. Purified lipase had an optimal pH and a temperature of 8 and 37 degrees C, respectively.

Small-scale production of Burkholderia cepacia ATCC21808 lipase adapted to high-throughput screening.

The screening of variant libraries of recombinant Burkholderia cepacia ATCC21808 lipase generated in Escherichia coli is limited by expression difficulties that are mainly due to the formation of inclusion bodies. To circumvent these difficulties and provide an efficient small-scale screening protocol, the gene encoding the lipase from B. cepacia was expressed in various expression vectors. With the pFLAG-ATS-Lip-Hp construct, expression of up to 6807 U/L of culture was possible in Erlenmeyer flasks. The production protocol was miniaturized in 96 deep-well plates, yielding 1300 U/L of lipase in fusion with the FLAG tag. With this protocol, the activity was determined in less than 10 min for a full plate, with a coefficient of variance of about 25%. For validation, 18 mutants constructed by site-directed mutagenesis on position Valine 266 were screened. Nice variations of activity were detected and found to be in agreement with those obtained in Erlenmeyer flask cultures. The protocol enabled the identification of 5 mutants showing enhanced activity toward para-nitrophenyl butyrate.

Induction of enzymes of 2,4-dichlorophenoxyacetate degradation in Burkholderia cepacia 2a and toxicity of metabolic intermediates.

Burkholderia cepacia 2a inducibly degraded 2,4-dichlorophenoxyacetate (2,4-D) sequentially via 2,4-dichlorophenol, 3,5-dichlorocatechol, 2,4-dichloromuconate, 2-chloromuconolactone and 2-chloromaleylacetate. Cells grown on nutrient agar or broth grew on 2,4-D-salts only if first passaged on 4-hydroxybenzoate- or succinate-salts agar. Buffered suspensions of 4-hydroxybenzoate-grown cells did not adapt to 2,4-D or 3,5-dichlorocatechol, but responded to 2,4-dichlorophenol at concentrations <0.4 mM. Uptake of 2,4-dichlorophenol by non-induced cells displayed a type S (cooperative uptake) uptake isotherm in which the accelerated uptake of the phenol began before the equivalent of a surface monolayer had been adsorbed, and growth inhibition corresponded with the acquisition of 2.2-fold excess of phenol required for the establishment of the monolayer. No evidence of saturation was seen even at 2 mM 2,4-dichlorophenol, possibly due to absorption by intracellular poly-beta-hydroxybutyrate inclusions. With increasing concentration, 2,4-dichlorophenol caused progressive cell membrane damage and, sequentially, leakage of intracellular K(+), P(i), ribose and material absorbing light at 260 nm (presumed nucleotide cofactors), until at 0.4 mM, protein synthesis and enzyme induction were forestalled. Growth of non-adapted cells was inhibited by 0.35 mM 2,4-dichlorophenol and 0.25 mM 3,5-dichlorocatechol; the corresponding minimum bacteriocidal concentrations were 0.45 and 0.35 mM. Strain 2a grew in chemostat culture on carbon-limited media containing 2,4-D, with an apparent growth yield coefficient of 0.23, and on 2,4-dichlorophenol. Growth on 3,5-dichlorocatechol did not occur without a supplement of succinate, probably due to accumulation of toxic quantities of quinonoid and polymerisation products. Cells grown on these compounds were active towards all three, but not when grown on other substrates. The enzymes of the pathway therefore appeared to be induced by 3,5-dichlorocatechol or some later metabolite. A possible reason is offered for the environmental persistence of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T).

Study of the mode of action of a polygalacturonase from the phytopathogen Burkholderia cepacia.

We have recently isolated and heterologously expressed BcPeh28A, an endopolygalacturonase from the phytopathogenic Gram-negative bacterium Burkholderia cepacia. Endopolygalacturonases belong to glycoside hydrolase family 28 and are responsible for the hydrolysis of the non-esterified regions of pectins. The mode of action of BcPeh28A on different substrates has been investigated and its enzymatic mechanism elucidated. The hydrolysis of polygalacturonate indicates that BcPeh28A is a non-processive enzyme that releases oligomers with chain lengths ranging from two to eight. By inspection of product progression curves, a kinetic model has been generated and extensively tested. It has been used to derive the kinetic parameters that describe the time course of the formation of six predominant products. Moreover, an investigation of the enzymatic activity on shorter substrates that differ in their overall length and methylation patterns sheds light on the architecture of the BcPeh28A active site. Specifically the tolerance of individual sites towards methylated saccharide units was rationalized on the basis of the hydrolysis of hexagalacturonides with different methylation patterns.

Preparation of cross-linked enzyme aggregates by using bovine serum albumin as a proteic feeder.

Addition of bovine serum albumin (BSA) as a proteic feeder facilitates obtaining cross-linked enzyme aggregates (CLEAs) in cases where the protein concentration in the enzyme preparation is low and/or the enzyme activity is vulnerable to the high concentration of glutaraldehyde required to obtain aggregates. CLEAs of Pseudomonas cepacia lipase and penicillin acylase were prepared. CLEA of lipase prepared in the presence of BSA retained 100% activity whereas CLEA prepared without BSA retained only 0.4% activity of the starting enzyme preparation. Lipase CLEA showed 12-fold increase in activity over free enzyme powder when the CLEA was used in transesterification of tributyrin. For the transesterification of Jatropha oil, while free enzyme powder required 8 h and 50 mg lipase to obtain 77% conversion, CLEA required only 6 h and 6.25 mg lipase to obtain 90% conversion. In the case of penicillin acylase, 86% activity could be retained in CLEA prepared with BSA whereas CLEA made without BSA retained only 50% activity. CLEA prepared without BSA lost 20% activity after 8 h at 45 degrees C whereas CLEA with BSA retained full activity. CLEA prepared with BSA showed Vmax/Km of 36.3 min-1 whereas CLEA prepared without BSA had Vmax/Km of 17.4 min-1 only. Scanning electron microscopy analysis showed that CLEAs prepared in the presence of BSA were less amorphous and closer in morphology to CLEAs of other enzymes described in the literature.

Covalent-bonded immobilization of lipase on poly(phenylene sulfide) dendrimers and their hydrolysis ability.

Covalent-bonded immobilization of lipase from burkholderia cepacia onto two poly(phenylene sulfide) (PPS) dendrimers with different generations (two and three) was achieved using carbodiimide as a coupling reagent. The hydrolysis activity of olive oil to fatty acid was studied on enzyme-immobilized PPS dendrimers. Enzyme activity was proportional to the enzyme loading, and highest recovered activity was obtained at the medium enzyme loading for both G2 and G3 dendrimers. The immobilization improved the optimum pH and caused the temperature range to widen. Immobilization of enzyme has enhanced the thermal stability of enzyme activity in comparison with free enzyme. The immobilized enzyme as a biocatalyst for batch hydrolysis of olive oil retained 80 approximately 90% activity even after 20 times of recycling. This retention of activity after recycle is very valuable and powerful in enzyme technology. The present noteworthy and vital availability on enzyme reaction of the covalently bonded immobilized lipase on dendrimer came from the structure of dendrimer with a large number of functional terminal groups, which are easily available for immobilization of many lipases at the situation keeping reactive enzymes on the surface of dendrimer.

Lipase-catalyzed ethanolysis of borage oil: a kinetic study.

Ethanolysis of borage oil catalyzed by two commercial lipases (from Pseudomonas cepacia and Candida antarctica) was studied using two different methodologies. Multiresponse models derived from a generalized Michaelis-Menten mechanism were utilized to describe the rates of formation of ethyl esters of the primary fatty acids present in the precursor oil. The relative rate constants determined for each of the fatty acid residues indicated that both lipases discriminate against release of gamma-linolenic acid residues under the reaction conditions studied. However, both lipases also released some of the residues located at the sn-2 position, indicating that for the experimental conditions studied, both lipases are nonspecific. Moreover, inactivation of Novozym 435 was rapid. Because the half-life of this enzyme (ca. 2.2 h) is comparable to the half-life of the reaction, the intrinsic reaction rate and enzyme deactivation must both be considered in modeling the kinetics.