Analysis of peroxidase activity of rice (Oryza sativa) recombinant hemoglobin 1: Implications for in vivo function of hexacoordinate non-symbiotic hemoglobins in plants

In plants, it has been proposed that hexacoordinate (class 1) non-symbiotic Hbs (nsHb-1) function in vivo as peroxidases. However, little is known about peroxidase activity of nsHb-1. We evaluated the peroxidase activity of rice recombinant Hb1 (a nsHb-1) by using the guaiacol/H₂O₂ system at pH 6.0 and compared it to that from horseradish peroxidase (HRP). Results showed that the affinity of rice Hb1 for H₂O₂ was 86-times lower than that of HRP (K_m = 23.3 and 0.27 mM, respectively) and that the catalytic efficiency of rice Hb1 for the oxidation of guaiacol using H₂O₂ as electron donor was 2838-times lower than that of HRP (k_cat/K_m = 15.8 and 44 833 mM⁻¹ min⁻¹, respectively). Also, results from this work showed that rice Hb1 is not chemically modified and binds CO after incubation with high H₂O₂ concentration, and that it poorly protects recombinant Escherichia coli from H₂O₂ stress. These observations indicate that rice Hb1 inefficiently scavenges H₂O₂ as compared to a typical plant peroxidase, thus indicating that non-symbiotic Hbs are unlikely to function as peroxidases in planta.     

Chemiluminescent determination of H2O2 using 4-(1,2,4-triazol-1-yl)phenol as an enhancer based on the immobilization of horseradish peroxidase onto magnetic beads

This article describes the employment of a novel p-phenol derivative, 4-(1,2,4-triazol-1-yl)phenol (TRP), as a highly potent signal enhancer of the luminol-hydrogen peroxide (H₂O₂)-horseradish peroxidase (HRP) chemiluminescence (CL) system. The CL reaction conditions were optimized, and the enhancement characteristics of TRP were compared with those of p-iodophenol (PIP). TRP produced a strong enhancement of the CL with the effect of prolonging the light emission. The developed system was then applied to the determination of H₂O₂ with immobilized HRP using magnetic beads as a solid support. The linear range for H₂O₂ was 2.0 × 10⁻⁶ to 1.0 × 10⁻³ M. The detection limit for H₂O₂ was 2.0 × 10⁻⁶ M. The proposed sensor was applied successfully to the determination of H₂O₂ in rainwater.     

Interaction between lanthanum ion and horseradish peroxidase in vitro

The interaction between lanthanum ion (La³⁺) and horseradish peroxidase (HRP) in vitro was investigated using a combination of biophysical and biochemical methods. When the molar ratio of La³⁺ and HRP is low, it was found that the interaction between La³⁺ and HRP mainly depends on the electrostatic attraction, van der waals force and hydrogen bond etc. Thus, the interaction is weak and the La–HRP complex cannot be formed in vitro. As expected, the interaction can change the conformation of HRP molecule, leading to the increase in the non-planarity of the porphyrin ring in the heme group of HRP molecule, and then in the exposure degree of the active center, Fe(III) of the porphyrin ring of HRP molecule. Therefore, the catalytic activity of HRP for the H₂O₂ reduction is improved. When the molar ratio of La³⁺ and HRP is high, La³⁺ can strongly coordinate with O and/or N in the amide group of the polypeptide chain of HRP molecule, forming the La–HRP complex. The formation of the La–HRP complex causes the change in the conformation of HRP molecule, leading to the decrease in the non-planarity of the porphyrin ring in the heme group of HRP molecule, and then in the exposure degree of the active center, Fe(III) of the porphyrin ring of HRP molecule. Thus, the catalytic activity of HRP for the H₂O₂ reduction is decreased comparing with that of HRP in the absence of La³⁺. The results can provide some references for understanding the interaction mechanism between trace elements ions and peroxidase in living organisms.     

Polymerization of guaiacol by lignin-degrading manganese peroxidase from Bjerkandera adusta in aqueous organic solvents

 Lignin-degrading manganese (II) peroxidase (MnP) purified from the culture of a wood-rotting basidiomycete, Bjerkandera adusta, was used in the polymerization of guaiacol. MnP was found to catalyze polymerization of guaiacol in 50% aqueous acetone, dimethyl formamide, methanol, ethanol, dioxane, acetonitrile, ethylene glycol and methylcellosolve. Maximum yield of polyguaiacol was achieved in 50% aqueous acetone. The weight average molecular weight (M _w) of the polymer was estimated to be 30 300 by gel permeation chromatography. However, matrix-assisted laser desorption ionization time of flight mass spectroscopy (MALDI-TOF-MS) analysis gave a more reliable M _w of 1690. IR, ¹³C-NMR, MALDI-TOF-MS and pyrolysis GC-MS analyses showed the presence of C–C and C–O linkages and quinone structure in polyguaiacol. It was also indicated that polyguaiacol has a methoxy-phenyl group as the terminal moiety. This suggests that polyguaiacol is a branched polymer in which guaiacol units are cross-linked at the phenolic group. Thermal gravimetric and differential scanning calorimetric analyses were also carried out. MnP also catalyzed the polymerization of o-cresol, 2,6-dimethoxyphenol and other phenolic compounds and aromatic amines. M _w of these polymers ranged from around 1000 to 1500. Received: 2 August 1999 / Received revision: 10 December 1999 / Accepted: 4 January 2000     

Polymerization of Horseradish Peroxidase by a Laccase‐Catalyzed Tyrosine Coupling Reaction

The polymerization of proteins can create newly active and large bio‐macromolecular assemblies that exhibit unique functionalities depending on the properties of the building block proteins and the protein units in polymers. Herein, the first enzymatic polymerization of horseradish peroxidase (HRP) is reported. Recombinant HRPs fused with a tyrosine‐tag (Y‐tag) through a flexible linker at the N‐ and/or C‐termini are expressed in silkworm, Bombyx mori. Trametes sp. laccase (TL) is used to activate the tyrosine of Y‐tagged HRPs with molecular O₂ to form a tyrosyl‐free radical, which initiates the tyrosine coupling reaction between the HRP units. A covalent dityrosine linkage is also formed through a HRP‐catalyzed self‐crosslinking reaction in the presence of H₂O₂. The addition of H₂O₂ in the self‐polymerization of Y‐tagged HRPs results in lower activity of the HRP polymers, whereas TL provides site‐selectivity, mild reaction conditions and maintains the activity of the polymeric products. The cocrosslinking of Y‐tagged HRPs and HRP‐protein G (Y‐HRP‐pG) units catalyzed by TL shows a higher signal in enzyme‐linked immunosorbent assay (ELISA) than the genetically pG‐fused HRP, Y‐HRP‐pG, and its polymers. This new enzymatic polymerization of HRP promises to provide highly active and functionalized polymers for biomedical applications and diagnostics probes.     

A carbon nanotube/silica sol–gel architecture for immobilization of horseradish peroxidase for electrochemical biosensor

A novel third-generation biosensor for hydrogen peroxide (H₂O₂) has been constructed based on horseradish peroxidase (HRP) immobilized by the sol–gel (SG) technology on carbon nanotube (CNT)-modified electrode. CNT has good promotion effects on the direct electron transfer between HRP and the electrode surface and the SG network provides a biocompatible microenvironment for enzyme. The immobilized HRP retained its bioelectrocatalytic activity for the reduction of hydrogen peroxide and can respond to the change of concentration of H₂O₂ rapidly. The heterogeneous electron transfer rate constant was evaluated to be 2.8 ± 0.4 s⁻¹. The amperometric response to H₂O₂ shows a linear relation in the range from 0.5 to 300 μmol l⁻¹ and a detection limit of 0.1 μmol l⁻¹ (S/N = 3). The K _M^app value of HRP immobilized on the electrode surface was found to be 1.35 mmol l⁻¹. The biosensor exhibited high sensitivity, rapid response and excellent long-term stability.     

Activation of indole-3-acetic acid oxidase from horseradish and Prunus by phenols and H2O2

The enzyme-catalysed oxidation of indole-3-acetic acid (IAA) was sytematically investigated with respect to enzyme source and cofactor influence using differential spectrophotometry and oxygen uptake measurement. Commercially-available horseradish peroxidase (HRP) and a peroxidase preparation from Prunus phloem showed identical catalytic properties in degrading IAA. There was no lag phase of IAA oxidation with any of the reaction mixtures tested. Monophenols exhibited a much stronger stimulatory effect than inorganic cofactors, but during the incubation of IAA the phenols were also gradually oxidised. Hydrogen peroxide (H₂O₂) in combination with monophenols accelerated peroxidation of the monophenol and IAA oxidation simutaneously. Since photometric determination of IAA was affected by oxidation products of dichlorophenol or phenol contamination of the enzyme preparation used, the standard IAA absorption measurements appear to be susceptible to methodological errors. Under certain incubation conditions a catalase-like activity of HRP during the course of IAA oxidation was noted and substrate inhibition was observed above 1.5 × 10^\s-4 M IAA. Some concepts concerning the mode of activation of the enzyme-catalysed IAA oxidation are deduced from the experimental results.     

Preparation and characterization of the layered borophosphates M(H2O)2[B2P2O8(OH)2]·H2O (M = Fe, Co, Ni)

The isotypic layered transition metal borophosphates M^II(H₂O)₂[B₂P₂O₈(OH)₂]·H₂O (M^II = Fe, Co, Ni) were prepared under hydrothermal conditions. Their crystal structures were determined by single-crystal X-ray diffraction data and revealed an isotypic relationship to Mg(H₂O)₂[B₂P₂O₈(OH)₂]·H₂O, a structure containing wavy 6³ nets formed by tetrahedral phosphate and hydrogenborate groups interconnected in an alternating fashion by sharing common apices. The crystalline compounds were also characterized by chemical analyses, scanning electron microscopy, energy dispersive X-ray analyses, thermal analyses, IR-spectroscopy and magnetic susceptibility measurements.     

Competing two enzymatic reactions realizing one‐step preparation of cell‐enclosing duplex microcapsules

The usefulness of cell‐enclosing microcapsules in biomedical and biopharmaceutical fields is widely recognized. In this study, we developed a method enabling the preparation of microcapsules with a liquid core in one step using two enzymatic reactions, both of which consume H₂O₂ competitively. The microcapsule membrane prepared in this study is composed of the hydrogel obtained from an alginate derivative possessing phenolic hydroxyl moieties (Alg‐Ph). The cell‐enclosing microcapsules with a hollow core were obtained by extruding an aqueous solution of Alg‐Ph containing horseradish peroxidase (HRP), catalase, and cells into a co‐flowing stream of liquid paraffin containing H₂O₂. Formation of the microcapsule membrane progressed from the surface of the droplets through HRP‐catalyzed cross‐linking of Ph moieties by consuming H₂O₂ supplied from the ambient liquid paraffin. A hollow core structure was induced by catalase‐catalyzed decomposition of H₂O₂ resulting in the center region being at an insufficient level of H₂O₂. The viability of HeLa cells was 93.1% immediately after encapsulation in the microcapsules with about 250 µm diameter obtained from an aqueous solution of 2.5% (w/v) Alg‐Ph, 100 units mL^?1 HRP, 9.1 × 10⁴ units mL^?1 catalase. The enclosed cells grew much faster than those in the microparticles with a solid core. In addition, the thickness of microcapsule membrane could be controlled by changing the concentrations of HRP and catalase in the range of 13–48 µm. The proposed method could be versatile for preparing the microcapsules from the other polymer derivatives of carboxymetylcellulose and gelatin. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:1528–1534, 2013     

Effects of H2O2 on the growth, secretion, and metabolism of hybridoma cells in culture

Summary The effect of low concentrations of hydrogen peroxide (H₂O₂) (5 × 10⁻⁷−9.5 × 10⁻⁷ M) on cell growth and antibody production was investigated with murine hybridoma cells (Mark 3 and anti-hPL) in culture. Cell growth, measured by flow cytometry with morphological parameters, was significantly stimulated by H₂O₂ (8 × 10⁻⁷ M) but H₂O₂ concentration of 7 × 10⁻⁶ M and above increased cell death. H₂O₂ stimulation of antibody production was nonsignificant. The metabolism of cells treated with 8 × 10⁻⁷ or 1 × 10⁻⁵ M H₂O₂ was similar to that of the control in terms of glucose and glutamine consumption, lactate and ammonia production, and amino acid concentrations in the medium. The concentrations of lactate dehydrogenase, a marker of cell death, in test and control cells were similar. However, concentrations of intracellular free radicals measured by flow cytometry with dihydrorhodamine 123 (DHR 123) and dichlorofluorescein diacetate (DCFH-DA) as fluorochromes were different. The reactive oxygen species content of cells in 8 × 10⁻⁷ M H₂O₂ was similar to that of the controls, but there was a sudden, marked production of superoxide anions (detected with DHR 123) and H₂O₂ or peroxides (detected with DCFH-DA) by cells incubated with 1 × 10⁻⁵ M H₂O₂ which increased with increasing H₂O₂ until cell death.     

Enhanced detection of H2O2 in cells expressing Horseradish Peroxidase

A new procedure for fluorescent detection of intracellular H₂O₂ in cells transiently expressing the catalyst Horseradish Peroxidase (HRP) is setup and validated. More specific reaction with HRP largely amplifies oxidation of the redox probes used (2′,7′-dichlorodihydrofluorescein and dihydrorhodamine). Expression of HRP does not affect cell viability. The procedure reveals MAO activity, a primary intracellular H₂O₂ source, in monolayers of intact transfected cells. The probes oxidation rate responds specifically to the MAO activation/inhibition. Their oxidation by MAO-derived H₂O₂ is sensitive to intracellular H₂O₂ competitors: it decreases when H₂O₂ is removed by pyruvate and it increases when the GSH-dependent removal systems are impaired. Specific response was also measured after addition of extracellular H₂O₂. Oxidation of the fluorescent probes following reaction of H₂O₂ with endogenous HRP overcomes most criticisms in their use for intracellular H₂O₂ detection. The method can be applied for direct determination in plate reader and is proposed to detect H₂O₂ generation in physio-pathological cell models.     

Kinetic study of peroxidase-catalyzed oxidation of 1-hydroxypyrene. Development of a nanomolar hydrogen peroxide detection system

Kinetics of 1-hydroxypyrene (1-HP) oxidation catalyzed with recombinant Coprinus cinereus (rCiP) and horseradish (HRP) peroxidases was investigated with a special emphasis for developing a nanomolar hydrogen peroxide (H₂O₂) detection system. At pH 8.0 the bimolecular constants of 1-HP oxidation with the ferryl compounds of rCiP and HRP were equal to (1.0 ± 0.3) × 10⁸ M⁻¹ s⁻¹ and (0.6 ± 0.2) × 10⁸ M⁻¹ s⁻¹, respectively. High bimolecular constants and fluorescence quantum yield of 1-HP (0.66) permitted detection as low as 21 nM of H₂O₂. To optimize the detection system 1-HP oxidation was modeled at steady-state conditions in the range pH 5.0 to pH 8.0. The 1-HP based detection system was compared with the Amplex Red system. The peroxidase-catalyzed 1-HP oxidation system was used for determination of ozone in the air.     

Hymenolepis diminuta: Chloride fluxes and membrane potentials associated with sodium-coupled glucose transport

Glucose transport by Hymenolepis diminuta was inhibited when Cl^? in the bathing medium was replaced with acetate (C₂H₃O₂^Post?), but was unaffected when Cl^? was replaced with SCN^?. The relative effectiveness of the anions to inhibit influx of 7.4 mM Cl^? in the presence of 1 mM glucose was SCN^? > Cl^? > C₂H₃O₂^Post?. Glucose stimulated the influxes of 120 mM Cl^? and SCN^?, but had little effect on 120 mM C₂H₃O₂^Post? influx. While the diffusion rates of the anions were C₂H₃O₂^Post? > SCN^? = Cl^?, the preference of the glucose transport system for the anions was SCN^? > Cl^? > C₂H₃O₂^Post?. Efflux of Cl^? was not affected by the rate of glucose influx. Finally, microelectrode recordings of worms anesthetized with 2 mM arecoline revealed a transmembrane potential (TMP) of ?45 ± 3.6 mV (inside negative). Three to four minutes after addition of glucose (5 mM) there was a progressive hyperpolarization of the TMP to ?58 mV. A revised model of the glucose transport system that is consistent with previous observations on this organism is proposed.     

Characterization of lecithin:Cholesterol acyltransferase from human plasma: II. Physical properties of the enzyme

The physical properties of purified human plasma lecithin:cholesterol acyltransferase (LCAT) were investigated by techniques including analytical ultracentrifugation, ultraviolet spectroscopy, electrofocusing, and circular dichroism. The partial specific volume of LCAT was determined by sedimentation equilibrium ultracentrifugation experiments in H₂O and D₂O solutions (0.702 ml/g). The M_r was 67,000 by sodium dodecyl sulfate (SDS)-gel electrophoresis and 60,000 by sedimentation equilibrium ultracentrifugation. The discrepancy between the two sets of data presumably arose from the glycoprotein nature of the enzyme. Studies of the ultraviolet spectrum indicated that LCAT contained 6.5% ($\text{w}\text{w}$) tyrosine which corresponds to approximately 18 tyrosine residues/mol of LCAT (polypeptide M_r 45,000). Spectrophotometric titration of the ionizable phenolic side chains indicated that nearly all the tyrosine residues were buried at neutral pH while they became gradually exposed at higher pH. The apparent pK of this transition was about 12.0 contrasted with 9.8, the apparent pK of ionization of the free tyrosyl groups.     

Nitroxides protect horseradish peroxidase from H2O2-induced inactivation and modulate its catalase-like activity

BackgroundHorseradish peroxidase (HRP) catalyzes H₂O₂ dismutation while undergoing heme inactivation. The mechanism underlying this process has not been fully elucidated. The effects of nitroxides, which protect metmyoglobin and methemoglobin against H₂O₂-induced inactivation, have been investigated.MethodsHRP reaction with H₂O₂ was studied by following H₂O₂ depletion, O₂ evolution and heme spectral changes. Nitroxide concentration was followed by EPR spectroscopy, and its reactions with the oxidized heme species were studied using stopped-flow.ResultsNitroxide protects HRP against H₂O₂-induced inactivation. The rate of H₂O₂ dismutation in the presence of nitroxide obeys zero-order kinetics and increases as [nitroxide] increases. Nitroxide acts catalytically since its oxidized form is readily reduced to the nitroxide mainly by H₂O₂. The nitroxide efficacy follows the order 2,2,6,6-tetramethyl-piperidine-N-oxyl (TPO) > 4-OH-TPO > 3-carbamoyl proxyl > 4-oxo-TPO, which correlates with the order of the rate constants of nitroxide reactions with compounds I, II, and III.ConclusionsNitroxide catalytically protects HRP against inactivation induced by H₂O₂ while modulating its catalase-like activity. The protective role of nitroxide at μM concentrations is attributed to its efficient oxidation by P940, which is the precursor of the inactivated form P670. Modeling the dismutation kinetics in the presence of nitroxide adequately fits the experimental data. In the absence of nitroxide the simulation fits the observed kinetics only if it does not include the formation of a Michaelis-Menten complex.General SignificanceNitroxides catalytically protect heme proteins against inactivation induced by H₂O₂ revealing an additional role played by nitroxide antioxidants in vivo.     

Preparation and solution properties of pullulan fractions as standard samples for water-soluble polymers

A series of pullulan fractions with molecular weights in the range 5 × 10³ to 8 × 10⁵ were prepared. The weight-average molecular weight (M_w) of all the samples was determined by sedimentation equilibrium. The hydrodynamic properties of pullulan in aqueous solution were investigated by viscometry and ultracentrifugation. The experimental results indicate that pullulan molecules in water are fairly stable and behave as expanded random coils when M_w is above 2 × 10⁴. The molecular weight distributions of the fractions were measured by gel filtration. The ratio M_w/M_n was close to 1·1, except for a sample with the highest M_w.It is concluded that the pullulan fractions prepared by the present work are well characterized and have a narrow molecular weight distribution. They may be useful as standard samples for studies of water-soluble polymers.     

Synergetic effects of Ca2+ and Cu2+ on phase transition in phosphatidylserine membranes

In complexes of divalent metals with large exchange rate constant (K_H2O) of the coordinated H₂O, such as Ca²⁺ and Cu²⁺, the cubic structure in the ligand field is usually unstable and conformation changes are easily induced. We observed the molecular motion of phosphatidylserine (PS) in an amphipathic solvent (water / methanol / chloroform) by ¹H-NMR and ESR using Ca²⁺ and / or Cu²⁺, which has a similar K_H2O to that of Ca²⁺. We found that Ca²⁺ did not hinder the molecular movements of PS. However, Cu²⁺ reduced the movements of both headgroups and the double bonds in the fatty acids of PS. By addition of both Ca²⁺ and Cu²⁺, phase transition to a soft solid phase in the PS membrane was observed at room temperature. The results indicate that the headgroups are clustered in two-dimensional network with each ligand field displaced from the aqueous phase to the water / oil interface. The structure changes of the polar headgroups after the binding of divalent cations are considered to trigger the phase transition of this acidic phospholipid membrane.     

Synthesis and properties of horseradish peroxidase copolymers

Conditions for copolymerization of native and sodium periodate-oxidized horseradish peroxidase (HTP; EC 1.11.1.7) have been optimized. Copolymerization products have been characterized electrophoretically, spectrally, and kinetically. Copolymers containing 2–3, 4, 5–7, and 9–10 molecules of the enzyme were found among the products of polymerization. The copolymers had lower values of D ₄₀₃/D ₂₈₀ than HRP. The copolymers had more ordered structures than the original HRP. Comparison of the thermal stability and kinetic characteristics of the fractions differing in the ratio of copolymers to the monomeric enzyme demonstrated that the polymeric products were more stable than HRP (in terms of resistance to high temperature or inhibitory effects of H₂O₂), but their kinetic activity was, on the whole, lower than that of the original enzyme.     

Cooxidation of phenol and 4-aminoantipyrin, catalyzed by polymers and copolymers of horseradish root peroxidase and Penicillium funiculosum 46.1 glucose oxidase

Polymers and copolymers of horseradish root peroxidase (HRP) and Penicillium funiculosum 46.1 glucose oxidase (GO) have been synthesized and their catalytic properties have been characterized (free and immobilized forms of each enzyme were studied). The cooxidation reaction of phenol and 4-aminoantipyrin (4-AAP), performed in an aqueous medium in the presence of equimolar amounts of GO and HRP, was characterized by effective K _M and k _cat of 0.58 mM and 20.9 s^?1 (for phenol), and 14.6 mM and 18.4 s^?1 (glucose), respectively. The catalytic efficiency of polymerization products (PPs) of GO (GO-PPs) depended on the extent of their aggregation. The combinations GO + HRP-PP and HRP + GO-PP, as well as the copolymer HRP*-GO-PP, proved promising as reagents for enzyme-based analytical systems. When adsorbed on aluminum hydroxide gels, GO-PPs exhibited higher catalytic activity than the non-polymeric enzyme. Maximum retention of GO-PP activity on the inorganic carrier was observed in the case of GO-PP copolymers with an activated HRP. Polymerization of HRP in the presence of a zinc hydroxide gel, paralleled by HRP-PP immobilization onto the gel, increased both the activity of the enzyme and its operational stability.     

Inactivation of cholinesterase induced by non-steroidal anti-inflammatory drugs with horseradish peroxidase: Implication for Alzheimer's disease

AimsTo clarify the mechanism of the protective effect of non-steroidal anti-inflammatory drugs (NSAIDs) on Alzheimer's disease, inactivation of cholinesterase (ChE) induced by NSAIDs was examined.Main methodsEquine ChE and rat brain homogenate were incubated with NSAIDs and horseradish peroxidase (HRP) and H₂O₂ (HRP–H₂O₂). ChE activity was measured by using 5,5'-dithiobis(nitrobenzoic acid). By using electron spin resonance, NSAID radicals induced by reaction with HRP–H₂O₂ were detected in the presence of spin trap agents.Key findingsEquine ChE was inactivated by mefenamic acid with HRP–H₂O₂. ChE activity in rat brain homogenate decreased dependent on the concentration of mefenamic acid in the presence of HRP–H₂O₂. NSAIDs diclofenac, indomethacin, phenylbutazone, piroxicam and salicylic acid inactivated ChE. Oxygen radical scavengers did not prevent inactivation of ChE induced by mefenamic acid with HRP–H₂O₂. However, spin trap agents 5,5-dimethyl-1-pyrroline-l-oxide and N-methyl-nitrosopropane, reduced glutathione and ascorbic acid strongly inhibited inactivation of ChE, indicating participation of mefenamic acid radicals. Fluorescent emission of ChE peaked at 400 nm, and the Vmax value of ChE changed during interaction of mefenamic acid with HRP–H₂O₂, indicating that ChE may be inactivated through modification of tyrosine residues by mefenamic radicals.SignificanceThe protective effect of NSAIDs on Alzheimer's disease seems to occur through inactivation of ChE induced by NSAIDs radicals.