Michaelis-Menten Kinetic Equation Research Articles

Porphyrin functionalized montmorillonite Loaded Cu2O-Fe3O4 as a sustainable peroxidase nanozyme for colorimetric determination of hydroquinone

Designing sustainable efficient peroxidase nanozymes and elucidating its peroxidase-like mechanism are very important for constructing colorimetric sensing platforms. Herein, a sustainable peroxidase nanozyme, porphyrin functionalized montmorillonite (PorMMT) loaded Cu2O-Fe3O4 nanocomposites, is prepared by the two-step hydrothermal method and can be recycled conveniently by virtue of magnetism of Fe3O4 from the composite (Cu2O-Fe3O4/PorMMT). Cu2O-Fe3O4/PorMMT peroxidase nanozyme can quickly catalyze the oxidation of the colourless substrate 3,3′,5,5′-tetramethylbiphenylamine (TMB) by H2O2 into a blue product (oxTMB) only in 3 min. Compared with pure MMT, Cu2O and Fe3O4 individual, Cu2O-Fe3O4/PorMMT exhibits the higher peroxidase-like activity. The catalytic activity of Cu2O-Fe3O4/PorMMT is reached the maximum at pH = 4 and T = 50 ℃. The catalytic behaviors of Cu2O-Fe3O4/PorMMT follow the Michaelis-Menten kinetic equation. The catalytic mechanism of Cu2O-Fe3O4/PorMMT is from the produced active species including superoxide free radicals (•O2−) and holes (h+). Based on the peroxidase-like activity of Cu2O-Fe3O4/PorMMT, a fast convenient colorimetric sensing platform has been designed to detect H2O2 and hydroquinone (HQ), respectively. H2O2 detection can be realized in the linear range of 510 mM with the limit of detection (LOD) of 2.68 mM, as well as hydroquinone (HQ) in the linear range of 550 μM with a much lower LOD of 4.37 μM. The convenient visual sensing platform has a potential application in monitoring HQ remains in lakes and rivers near dressing plants.

Mitochondrial Sensitivity To Submaximal ADP Concentrations Following Bed Rest: A Double Exponential Model Analysis

We recently demonstrated that a 10-day exposure to inactivity/microgravity (bed rest, BR) determined impairments of peak oxygen uptake (V̇O2), peak cardiac output, peripheral and microvascular function, whereas maximal ADP-stimulated mitochondrial respiration ex vivo in isolated permeabilized fibers and muscle V̇O2 off-kinetics in vivo were unaffected. PURPOSE: To evaluate mitochondrial sensitivity to submaximal [ADP]. METHODS: Isolated permeabilized vastus lateralis fibers were analyzed by high-resolution respirometry, before (PRE) and after (POST) a 10-day BR in 10 young males. 11 submaximal titrations of ADP (from 12.5 to 10,000 μM) were utilized to assess complex I + II-linked ADP sensitivity which was analyzed by both a Michaelis-Menten (MM) kinetics equation, with the calculation of the apparent Km by standard methods, and by applying a double-exponential function, with the calculation of [ADP] corresponding to 50% of the maximal mitochondrial respiration ([ADP] at 50% JO2max). RESULTS: The double-exponential function provided a better fitting of the data according to AIC model selection. The sum of squared residuals was substantially lower with the double-exponential vs. MM fitting (411 ± 419 and 1209 ± 495 [pmol/s/mg]2, respectively). R2 was higher with the double-exponential vs. the MM fitting (0.97 ± 0.04 and 0.90 ± 0.05, respectively). Analysis of residuals showed that the fitting by MM markedly overestimated JO2 from 1000 to 2000 μM, and underestimated JO2 from 6000 to 10,000 μM. The apparent Km for MM was lower than the [ADP] at 50% JO2max, both in PRE (843 ± 706 and 1270 ± 1015 μM, respectively) and in POST (375 ± 173 and 409 ± 398 μM, respectively). Only for the [ADP] at 50% JO2max the difference between POST vs. PRE was statistically significant (P = 0.046). CONCLUSIONS: The double-exponential function provided a better fit of experimental data. It might also give insights into cellular mechanisms regulating mitochondrial respiration, possibly related to the transport of nucleotides and phosphate across external and internal mitochondrial membranes, ATP synthase activity and respiratory chain activity. The enhanced mitochondrial sensitivity to submaximal [ADP] after BR could represent an attempt to maintain metabolic homeostasis in the presence of impairments upstream of mitochondria.

Relaxation effects of Eriobotrya japonica toward tracheal smooth muscle via action mechanism on histamine-1 receptor and phosphodiesterase-5 enzyme.

The Eriobotrya japonica leaves have the activity to relax the smooth muscle in the respiratory tract. However, the mechanism of action due to that activity has never been carried out. This study aims to determine the relaxation effects of E. japonica leaves extract in the isolated trachea of the guinea pigs through the inhibition of the histamine-1 (H-1) receptor and the phosphodiesterase-5 (PDE-5) enzyme. The determination of the relaxation effects was carried out by using histamine to contract smooth muscle within the tracheal tract, followed by adding cumulative concentrations of extract. Michaelis–Menten kinetics equation was used to determine the antagonist type of extract toward H-1 receptor. The understanding of mechanism of action of the extract toward PDE-5 enzyme was performed by incubating the smooth muscle using sildenafil. The percentage value of responses, originated from the relaxation effect of the extract toward the trachea was analyzed by using the t-independent test. The result showed that the extract was able to relax the smooth muscle, which was contracted by histamine, and there was a positive correlation between concentration and relaxation effect (P < 0.05; r = 0.973). The extract also antagonized the histamine as a noncompetitive antagonist. The incubation within the trachea with sildenafil demonstrated equal relaxation effect, produced by the extract. It can be concluded that E. japonica extract had relaxation effect within the isolated trachea as antagonist noncompetitive toward H-1 receptor and inhibitor of the PDE-5 enzyme.

Understanding the kinetics of catalysed reactions in microheterogeneous thin film electrodes

In this paper which is dedicated to Professor Richard Compton for his 65th birthday, we examine the problem of describing the transport and kinetics of catalytic reactions in which the catalyst is immobilized within a support matrix such as for example redox enzymes immobilized in a polymer matrix, to form a chemically modified electrode. We examine a mathematical procedure which enables a full analytical solution to the Michaelis-Menten kinetic rate equation when coupled to Ficksian diffusion in thin bounded film. This governing reaction/diffusion equation is non-linear and a full analytical solution has, up until very recently, not been developed. Analytical solutions valid for low and high substrate concentrations have been previously reported. This solution for the amperometric steady state current is accurate whatever the value of substrate concentration. The analysis is applied to diffusion/reaction in a planar slab. General analytical solutions valid for steady state conditions for both the amperometric and potentiometric sensor response are provided. We then extend this useful analysis to consider the effect of concentration polarization in the solution, and to consider the effect of competitive inhibition on the amperometric current response. Finally, the analysis is extended to a polymer modified electrode when a redox mediator is used in the polymer film. General expressions for the current are obtained which were valid for any value of the substrate concentration. Kinetic case diagrams are developed and nine approximate limiting expressions for the amperometric response at steady state when the catalytic matrix is either conducting or insulating are developed.

An electrochemical hydrogen peroxide sensor for applications in nuclear industry

Hydrogen peroxide is a radiolysis product of water formed under gamma-irradiation; therefore, its reliable detection is crucial in the nuclear industry for spent fuel management and coolant chemistry. This study proposes an electrochemical sensor for hydrogen peroxide detection. Cysteamine (CYST), gold nanoparticles (GNPs), and horseradish peroxidase (HRP) were used in the modification of a gold electrode for fabricating Au/CYST/GNP/HRP sensor. Each modification step of the electrode was investigated through electrochemical and physical methods. The sensor exhibited strong sensitivity and stability for the detection and measurement of hydrogen peroxide with a linear range of 1–9 mM. In addition, the Michaelis–Menten kinetic equation was applied to predict the reaction curve, and a quantitative method to define the dynamic range is suggested. The sensor is highly sensitive to H2O2 and can be applied as an electrochemical H2O2-sensor in the nuclear industry.

增温与氮添加对不同季节杉木幼苗细根不同形态氮吸收动力学的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 增温与氮添加对不同季节杉木幼苗细根不同形态氮吸收动力学的影响 DOI: 10.5846/stxb201905070924 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金重点项目（31830014） Effects of warming and nitrogen addition on nitrogen uptake kinetics of fine roots of Cunninghamia lanceolata seedlings in different seasons Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为了揭示不同季节下杉木人工林不同形态氮吸收速率对全球变暖与氮沉降的地下响应，在福建三明森林生态系统与全球变化研究站陈大观测点开展增温和氮添加双因子试验，包括对照、增温、施氮、增温+施氮4个处理。结果表明：（1）在三个季节中，4个处理的杉木细根对不同浓度下硝态氮的吸收速率基本呈现出春季较高，夏秋季较低的态势，而对不同浓度下铵态氮的吸收速率则相反，为夏秋季较高，春季较低。（2）不同季节四个处理的离体根对不同浓度下铵态氮的吸收均遵循米氏-曼氏动力学方程，而对硝态氮的吸收并不完全遵循米氏方程，表现为双相动力学。（3）春季，与无氮添加相比，氮添加提高了NH4+的最大吸收速率（Vmax-NH4+）。夏季，与无增温相比，增温提高了Vmax-NH4+。秋季，与无增温相比，增温降低了NH4+的半饱和常数（Km-NH4+）；与无氮添加相比，氮添加提高了Km-NH4+。增温与氮添加对不同季节100 μmol时的硝态氮吸收速率（V100-NO3-）都没有显著影响。增温与氮添加对不同季节Vmax-NH4+、Km-NH4+和V100-NO3-都没有显著的交互作用。本研究表明增温会提高杉木幼苗夏秋季的NH4+吸收能力，而氮添加会提高春季的NH4+吸收能力，降低秋季的NH4+吸收能力，但增温与氮添加并不会改变不同季节的NO3-吸收能力。 Abstract:In order to reveal the influence of global warming and nitrogen addition on the ecological process of Chinese fir (Cunninghamia lanceolata) seedlings, we conducted a two-factor experiment of warming and nitrogen addition, which consisted control, warming, nitrogen addition, and warming+nitrogen addition. The study site is located in Forest Ecosystem and Global Change Research Station of Fujian Normal University in Chenda, Sanming, Fujian Province. The results showed that: (1) the absorption rate of nitrate nitrogen by the fine roots of C. lanceolata under different concentrations was higher in spring and lower in summer and autumn, but the absorption rate of ammonium nitrogen was higher in summer and autumn and lower in spring. (2) The absorption of ammonium nitrogen by the four treatments followed the Michaelis-Menten kinetic equation, but the absorption of nitrate nitrogen did not fully followed it, which showed dual-phase kinetics in different seasons. (3) In spring, compared with nitrogen-free addition, nitrogen addition increased the maximum velocity of NH4+ (Vmax-NH4+). In summer, compared with no warming, the warming increased Vmax-NH4+. In autumn, compared with no warming, the warming decreased the Michaelis-Menten constant (Km-NH4+); compared with nitrogen-free addition, nitrogen addition increased Km-NH4+. Warming and nitrogen addition had no significant effect on the absorption rate of nitrate nitrogen at 100 μmol (V100-NO3-) in different seasons, and there was no significant interaction between warming and nitrogen addition on Vmax-NH4+, Km-NH4+ and V100-NO3-in different seasons. The results indicated that warming would improve NH4+ absorption capacity of Chinese fir seedlings in summer and nitrogen addition would improve NH4+ absorption capacity in spring and reduce NH4+ absorption capacity in autumn, but warming and nitrogen addition would not change NO3- absorption capacity in different seasons. 参考文献 相似文献 引证文献

A new gastro-intestinal mathematical model to study drug bioavailability

This work focuses on a new mathematical model which describes the gastro-intestinal absorption of drugs and the effect of food interactions on drugs bioavailability. The model structure consists of five compartments (stomach, duodenum, jejunum feeding, intestine and blood) simulated though different in-series reactors. All the enzymatic reactions taking place in the gastro-intestinal system are described through the Michaelis–Menten kinetic equations. The model has been tested for drug administration (paracetamol and ketoprofen) with and without the meal digestion. The model has been validated through pharmacokinetics curves obtained from in vivo tests (reported in the literature) and used to simulate the drug absorption dynamics in different conditions. The maximum blood concentration were 0.153 mmol L−1 and 0.0243 mmol L−1, respectively for paracetamol and ketoprofen. The time to reach the maximum concentration for the paracetamol and ketoprofen was around 55 min. In case of contemporary meal digestion, the maximum concentration of paracetamol in the blood was 0.100 mmol L−1 and 0.0135 mmol L−1 for ketoprofen; the time to reach the maximum concentration was 3 h and 45 min for paracetamol and 3 h and 35 min for ketoprofen. The drugs showed different pharmacokinetics, in agreement with the literature, during the digestion of food. To show the predictive capacity of the model, the simulations were also compared against additional experimental data (obtained from in vivo tests available in the literature) relative to ketoprofen administration with food.

A label-free immunosensor based on PtPd NCs@MoS2 nanoenzymes for hepatitis B surface antigen detection

Nowadays, nanomaterials with enzymatic properties have aroused wide interest because of their special advantages, such as catalytic activity, simple preparation method and high stability. We introduced new nanoenzymes to a label-free electrochemical immunosensor for Hepatitis B surface antigen (HBs Ag) detection. In this study, PtPd nanocubes@MoS2 nanoenzymes (PtPd NCs@MoS2) were prepared by loading PtPd nanocubes (PtPd NCs) on molybdenum disulfide nano-sheet (MoS2) through in situ redox polymerization. The prepared nanoenzymes exhibited enhanced peroxidase-like activity than separate MoS2 and PtPd NCs. The catalytic process of PtPd NCs@MoS2 is in agreement with the Michaelis-Menten kinetic equation. PtPd NCs@MoS2 were used for sensitive detection of HBs Ag, which is ascribed to their superior peroxidase activity, good conductivity and high specific surface area and synergistic amplification for current signals. Compared with the detection limit of colorimetric method (3.3 pg/mL), the electrochemical method (10.2 fg/mL) shows a lower detection limit and a wider linear range from 32 fg/mL to 100 ng/mL, so it is more suitable for quantitative analysis of Hepatitis B. In summary, the prepared immunosensor provides a better opportunity for early diagnosis of Hepatitis B and also has further applications in biosensing and medical diagnostics.

Prediction of Ethylene Production Rate of Barangan Banana Using Kinetic Enzymatic Michaelis-Menten

MM is a model that describes the rate of reaction of product ethylene towards the substrate concentration and MMC is an enzymatic kinetics model to see the effect of the increase of O2 on the rate of reaction. The objective of the study was to estimate ethylene production rate in bananas by applying the Michaelis-Menten enzymatic kinetics equation. Barangan Banana with harvest age 11 and 10 weeks were measured respiration rate with continuous gas analyzer in temperature 10, 20, and 28 °C with 3 replications along measurement of ethylene production rate using ethylene meter obtained from a closed system method and represented by Michael-Menten equation. The temperature dependence was represented base on Arrhenius law. The model parameters (KmC2H4 dan rC2H4 max) are calculated using Lineweaver-Burk linier graph method. MM and MMC applications can be used to estimate ethylene production rate of Barangan banana. MM equation resulted that 11-week harvest age obtaining R2 was higher than 10 weeks 0.95 while the 10-week harvested R2 0.94. MMC equation, the 11-week harvest age R2 0.95 was higher compared to 10 weeks R2 0.94. It could be predicted that MM and MMC equations can predicted the rate of ethylene production of Barangan banana

On the Evaluation of Quantitative Parameters and Formal Kinetic Features of Nitrification in Natural Waters

Using the laboratory modeling method, it has been shown that the enzymatic Michaelis–Menten kinetics equation provides a reasonable description of nitrification process in natural waters. The reaction has the first rate order with respect to the enzyme and pseudo zero order with respect to the substrate (ammonium ion) in a large excess of the latter.

Investigation on phenol degradation capability of Scenedesmus regularis: influence of process parameters

ABSTRACTPhenol removal from environmental solutions has attracted much attention due to phenol’s high toxicity, even at low concentrations. This study aims to reveal the phenol biodegradation capacity of Scenedesmus regularis. Batch system parameters (pH, amount of algal cell, phenol concentration) on biodegradation were examined. After 24 h of treatment, 92.16, 94.50, 96.20, 80.53, 65.32, 52 and 40% of phenol were removed by Scenedesmus regularis in aqueous solutions containing 5, 10, 15, 20, 30, 40 and 50 mg/L of phenol, respectively. To describe the correlation between degradation rate and phenol concentration, the Michaelis–Menten kinetic equation was used where Vmax and Km are 0.82 mg phenol g algea−1 h−1 and 24.97 ppm, respectively. Phenol remediation ability of S.regularis can enable the usage of the spent biomass as biofuel feedstock and animal feed makes it a ‘green’ environmental sustainable process.

Simulating microbial denitrification with EPIC: Model description and evaluation

Microbial denitrification occurs in anaerobic soil microsites and aquatic environments leading to production of N2O and N2 gases, which eventually escape to the atmosphere. Atmospheric concentrations of N2O have been on the rise since the beginning of the industrial revolution due to large-scale manipulations of the N cycle in managed ecosystems, especially the use of synthetic nitrogenous fertilizer. Here we document and test a microbial denitrification model identified as IMWJ and implemented as a submodel in the EPIC terrestrial ecosystem model. The IMWJ model is resolved on an hourly time step using the concept that C oxidation releases electrons that drive a demand for electron acceptors such as O2 and oxides of N (NO3−, NO2−, and N2O). A spherical diffusion approach is used to describe O2 transport to microbial surfaces while a cylindrical diffusion method is employed to depict O2 transport to root surfaces. Oxygen uptake by microbes and roots is described with Michaelis-Menten kinetic equations. If insufficient O2 is present to accept all electrons generated, the deficit for electron acceptors may be met by oxides of nitrogen, if available. The movement of O2, CO2 and N2O through the soil profile is modeled using the gas transport equation solved on hourly or sub-hourly time steps. Bubbling equations also move N2O and N2 through the liquid phase to the soil surface under highly anaerobic conditions. We used results from a 2-yr field experiment conducted in 2007 and 2008 at a field site in southwest Michigan to test the ability of EPIC, with the IMWJ option, to capture the non-linear response of N2O fluxes as a function of increasing rates of N application to maize [Zea mays L.]. Nitrous oxide flux, soil inorganic N, and ancillary data from 2007 were used for EPIC calibration while 2008 data were used for independent model validation. Overall, EPIC reproduced well the timing and magnitude of N2O fluxes and NO3− mass in surficial soil layers after N fertilization. Although similar in magnitude, daily and cumulative simulated N2O fluxes followed a linear trend instead of the observed exponential trend. Further model testing of EPIC+IMWJ, alone or in ensembles with other models, using data from comprehensive experiments will be essential to discover areas of model improvement and increase the accuracy of N2O predictions under a wide range of environmental conditions.

Modeling of Complex Reductive Biodegradation Kinetics of Recalcitrant Organic Contaminants

AbstractA kinetic model based on the Michaelis-Menten kinetic equations for simulating the complex reductive biodegradation kinetics of groundwater contaminants was developed that incorporates mult...

Characterization and kinetic parameters of endo-1,4-β-d-glucanase of ultraviolet mutated Aspergillus niger and Penicillium citrinum

Mutagenic agents had been used to enhance production of enzymes in microorganisms, but the effects of the agents on the kinetic parameters and catalytic efficiency of the produced enzymes had not been critically evaluated. A study was conducted to assess the effects of ultraviolet (UV) mutagenesis on the kinetic parameters and catalytic efficiency of endo-1,4-β-D-glucanase enzyme obtained from wild and mutated strains of Aspergillus niger and Penicillium citrinum obtained from decaying wood wastes modified by ultraviolet radiation. The endo-1, 4-β-Dglucanase from both wild and mutant strains of the fungi were purified by centrifugation, ammonium sulfa-te precipitation and anion exchange chromatography using Sephadex A25-120 and Whatman DE-52 resins. The kinetic parameters determined from Lineweaver-Burk plot, using the velocity or reaction rates at varying concentrations of carboxymethyl cellulose substrate ranging from 0 - 20 mg/mL were validated by Hanes-Woolf plots for convergence, as the Michaelis-Menten kinetic equation is non-linear. The Michaelis-Menten constant (Km) and maximum velocity (Vmax) for the wild A. niger were 15.31 g/L and 4.67 g/L respectively, while values for corresponding mutated strain were 7.9 g/L and 3.39 g/L respectively. The Km and Vmax for wild P. citrinum were 7.94g/L and 6.81g/L respectively, while the values for the mutated strain were 6.60 g/L and 6.84 g/L respectively. Catalytic efficiency of endoglucanase of wild and mutated strains of A. niger were 0.305 and 0.42 M-1s-1 respectively, while the values for endoglucanase of wild and mutated strains of P. citrinum were 0.858 and 1.036 M-1s-1 respectively. Mutagenesis using ultraviolet radiation therefore enhanced the catalytic efficiency of endoglucanase enzyme.Keywords: Endo-1,4-β-D-glucanase, Aspergillus niger, Penicillium citrinum, UV Mutagenesis, Michaelis-Menten Kinetic Equation, Lineweaver-Burk Plot, Hanes Woolf Plot, Catalytic Efficiency

Kinetic modeling of fermentative hydrogen production by Thermotoga neapolitana

A kinetic model of fermentative hydrogen (H2) production was developed for the hyperthermophilic marine bacterium Thermotoga neapolitana DSMZ 4359T using glucose as the substrate. The model was built based on anaerobic digestion model no.1 (ADM1) by IWA using Monod-like kinetic equations. Several series of pH controlled batch fermentation tests were performed under pure CO2 or N2 atmosphere in serum bottles to evaluate the growth kinetic parameters. The kinetic parameters were estimated by applying the non-linear least square method to Monod and Michaelis–Menten kinetic equations. The experimentally estimated value of k, kS, Y and kd were 0.839 h−1, 1.42 g/L, 0.1204 and 0.0043 h−1, respectively. The kinetic parameters were analyzed for sensitivities and subsequently calibrated and validated by a separate set of experimental results. The model was particularly effective in estimating the biomass growth, substrate consumption, and H2 production except for acetate and lactate production, due to capnophilic condition (under CO2 atmosphere).

Exploring the Altered Dynamics of Mammalian Central Carbon Metabolic Pathway in Cancer Cells: A Classical Control Theoretic Approach

BackgroundIn contrast with normal cells, most of the cancer cells depend on aerobic glycolysis for energy production in the form of adenosine triphosphate (ATP) bypassing mitochondrial oxidative phosphorylation. Moreover, compared to normal cells, cancer cells exhibit higher consumption of glucose with higher production of lactate. Again, higher rate of glycolysis provides the necessary glycolytic intermediary precursors for DNA, protein and lipid synthesis to maintain high active proliferation of the tumor cells. In this scenario, classical control theory based approach may be useful to explore the altered dynamics of the cancer cells. Since the dynamics of the cancer cells is different from that of the normal cells, understanding their dynamics may lead to development of novel therapeutic strategies.MethodWe have developed a model based on the state space equations of classical control theory along with an order reduction technique to mimic the actual dynamic behavior of mammalian central carbon metabolic (CCM) pathway in normal cells. Here, we have modified Michaelis Menten kinetic equation to incorporate feedback mechanism along with perturbations and cross talks associated with a metabolic pathway. Furthermore, we have perturbed the proposed model to reduce the mitochondrial oxidative phosphorylation. Thereafter, we have connected proportional-integral (PI) controller(s) with the model for tuning it to behave like the CCM pathway of a cancer cell. This methodology allows one to track the altered dynamics mediated by different enzymes.Results and DiscussionsThe proposed model successfully mimics all the probable dynamics of the CCM pathway in normal cells. Moreover, experimental results demonstrate that in cancer cells, a coordination among enzymes catalyzing pentose phosphate pathway and intermediate glycolytic enzymes along with switching of pyruvate kinase (M2 isoform) plays an important role to maintain their altered dynamics.

A simple model to predict mass transfer rates and kinetics of biochemical and biomedical Michaelis–Menten surface reactions

In this paper we propose a simple algebraic equation to compute the steady and laminar mass transfer rate produced by a surface chemical reaction that follows the Michaelis–Menten kinetic equation. This kinetic model characterizes the chemical rates of many catalytic biochemical reactions and many enzymatic reactions and, consequently, the equation can be used in experiments to predict the mass transfer rate or to determine the kinetics of reactions occurring on functionalized surfaces. The proposed correlation has been obtained by fitting results of numerical simulations and it relates the surface averaged Sherwood number, or the non-dimensional mass transfer rate, with the Péclet number based on the shear rate, the Damkhöler number ( Da ) based on the maximal velocity and the non-dimensional Michaelis constant ( K M ∗ ). The validity of the correlation has been analyzed in the range of the non-dimensional parameters that can be found in physically realizable conditions. A procedure to determine experimentally the kinetic constants of the surface reaction is outlined and applied to experimental data.

2'-O-methyl nucleotide modified DNA substrates influence the cleavage efficiencies of BamHI and BglII.

Induction of endonucleolytic DNA cleavage is an essential event that links the initiating stimuli to the final effects of cells. The cleavage efficiency and thus the final yield could be affected by many factors, including structures of DNA substrates, composite structures of enzymes-substrates or enzymes-nucleic analogs and so on. However, it is not clear whether a nucleotide derivative-substituted in DNA substrates can influence the efficiency of enzymatic cleavage. To investigate the effect of sugar pucker conformation on DNA-protein interactions, we used 2'-O-methyl modified nucleotides (OMeN) to modify DNA substrates of isocaudemers BamHI and BglII in this study, and used FRET assay as an efficient method for analysis of enzyme cleavage. Experimental results demonstrated that OMeN-substituted recognition sequences influenced the cleavage rates significantly in a position-dependent manner. OMeN substitutions can reduce the cleavage as expected. Surprisingly, OMeN substitutions can also enhance the cleavage rates. The kinetics parameters of Vmax and Km have been obtained by fitting the Michaelis-Menten kinetic equation. These 2'- OMe nucleotides could behave as a regulatory element to modulate the enzymatic activity in vitro, and this property could enrich our understanding about the endonuclease cleavage mechanism and enhance our ability to regulate the enzymatic cleavage efficiency for applications in synthetic biology.

Interaction and biodegradation evaluate of m-cresol and quinoline in co-exist system

Environmentally hazardous and toxic chemicals are commonly generated in actual wastewater that the complex compositions in wastewater treatment system need different types of strains to be degraded. The main objective of this research was to understand the effect of extra substrates, phenolic and N-heterocyclic compounds, on the performance of pure cultural and mixed strains under single and dual substrates conditions. Two bacteria, Lysinibacillus sp. SC03 and Achromobacter sp. DN-06, were acclimated to degrade different concentrations of m-cresol and quinoline. The results indicated that Lysinibacillus sp. SC03 could completely degrade 100 mg l−1m-cresol with no delay time, however, little removal of quinoline was observed; Achromobacter sp. DN-06 could degrade 100 mg l−1 quinoline in 32 h, but could not remove m-cresol, which means m-cresol and quinoline is the specific substrate. The degradation rate of m-cresol fitted well to the zero-order kinetic equation although the degrading ability of Lysinibacillus sp. SC03 was inhibited when less than 100 mg l−1 quinoline was added, and the inhibitive effect was confirmed to be a noncompetitive pattern which could be interpreted by the Michaelis–Menten kinetics equation with corresponding parameters Vmax, Km, K1 and K2 were 13.16 mg l−1 h−1, 35.84 mg l−1, 200.0 mg l−1 and 285.7 mg l−1, respectively. Moreover, the addition of m-cresol-degrading strain (Lysinibacillus sp. SC03) could accelerate the removal of quinoline because the metabolites of quinoline could be degraded by Lysinibacillus sp. SC03 and the chemical equilibrium moved to more biodegradation of quinoline. Also, this process attributed to less the delay time during the quinoline removal.

Insights on How the Activity of an Endoglucanase Is Affected by Physical Properties of Insoluble Celluloses

Cellulose physical properties like crystallinity, porosity, and particle size are known to influence cellulase activity, but knowledge is still insufficient for activity prediction from such measurable substrate characteristics. With the aim of illuminating enzyme-substrate relationships, this work evaluates a purified hyperthermophilic endo-1,4-beta-glucanase (from Pyrococcus furiosus) acting on 13 celluloses characterized for crystallinity and crystal width (by X-ray diffraction), wet porosity (by thermoporometry), and particle size (by light scattering). Activities are analyzed by the Michaelis-Menten kinetic equation, which is justified by low enzyme-substrate affinity. Michaelis-Menten coefficients K(m) and k(cat) are reinterpreted in the context of heterogeneous cellulose hydrolysis. For a set of as-received and milled microcrystalline celluloses, activity is successfully described as a function of accessible substrate concentration, with accessibility proportional to K(m)(-1). Accessibility contribution from external particle areas, pore areas, and crystalline packing are discriminated to have comparable magnitudes, implying that activity prediction demands all these substrate properties to be considered. Results additionally suggest that looser crystalline packing increases the lengths of released cello-oligomers as well as the maximum endoglucanase specific activity (k(cat)).