Steady-state oxidation model by horseradish peroxidase for the estimation of the non-inactivation zone in the enzymatic removal of pentachlorophenol

Integrated Experimental and Theoretical Studies on an Electrochemical Immunosensor

Electrochemical immunosensors (EIs) integrate biorecognition molecules (e.g., antibodies) with redox enzymes (e.g., horseradish peroxidase) to combine the advantages of immunoassays (high sensitivity and selectivity) with those of electrochemical biosensors (quantitative electrical signal). However, the complex network of mass-transfer, catalysis, and electrochemical reaction steps that produce the electrical signal makes the design and optimization of EI systems challenging. This paper presents an integrated experimental and modeling framework to address this challenge. The framework includes (1) a mechanistic mathematical model that describes the rate of key mass-transfer and reaction steps; (2) a statistical-design-of-experiments study to optimize operating conditions and validate the mechanistic model; and (3) a novel dimensional analysis to assess the degree to which individual mass-transfer and reaction steps limit the EI's signal amplitude and sensitivity. The validated mechanistic model was able to predict the effect of four independent variables (working electrode overpotential, pH, and concentrations of catechol and hydrogen peroxide) on the EI's signal magnitude. The model was then used to calculate dimensionless groups, including Damkohler numbers, novel current-control coefficients, and sensitivity-control coefficients that indicated the extent to which the individual mass-transfer or reaction steps limited the EI's signal amplitude and sensitivity.

Influence of natural organic matter on horseradish peroxidase-mediated removal of 17α-ethinylestradiol: Role of molecular weight

Ubiquitous natural organic matter (NOM) plays a crucial role in the peroxidase-mediated transformation of phenolic pollutants in aquatic environment. As a poorly defined polydispersed mixture of assorted organic substances with wide molecular weight (MW) distribution, NOM has far prevented researchers from finding out the primarily responsible components for the specific effect. In this work, MW fractionated NOMs (Mf-NOMs) were used to investigate their roles on horseradish peroxidase (HRP)-mediated transformation of 17α-ethinylestradiol (EE2). The removal rate of EE2 was restrained in the presence of pristine or Mf-NOMs, and the inhibitory mechanism was MW-dependent. Low Mf-NOMs restrained the enzymatic reaction by acting as competitive substrates, while high Mf-NOMs retained freely dissolved EE2 which reduced its availability for enzymatic reaction. The contribution of these two processes to the inhibition induced by pristine NOM was further quantified and found to be relevant to the reaction conditions, especially EE2 concentration. The findings of this work reveal more complex influences of NOM on the enzymatic reaction than ever demonstrated, which aids in understanding the fate of EE2 and other congener contaminants in natural and municipal water.

Soybean peroxidase immobilized onto silica-coated superparamagnetic iron oxide nanoparticles: Effect of silica layer on the enzymatic activity

Peroxidase immobilization onto magnetic supports is considered an innovative strategy for the development of technologies that involves enzymes in wastewater treatment. In this work, magnetic biocatalysts were prepared by immobilization of soybean peroxidase (SBP) onto different silica-coated superparamagnetic iron oxide nanoparticles. The obtained magnetic biocatalysts were tested for the degradation of malachite green (MG), a pollutant often found in industrial wastewaters and with significant drawbacks for the human and environmental health. A deep physicochemical characterization of the materials was performed by means of X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), High Resolution-Transmission Electron Microscope (HR-TEM) and magnetization measurements among others techniques. Results showed high immobilization yield of SBP onto nanomaterials with excellent properties for magnetic recoverability. A partial loss of activity with respect to free SBP was observed, compatible with the modification of the conformational structure of the enzyme after immobilization. The structural modification depended on the amount (and thickness) of silica present in the hybrid materials and the activity yield of 43% was obtained for the best biocatalyst. Thermal stability and reusability capacity were also evaluated.

Enhanced bio-catalytic performance and dye degradation potential of chitosan-encapsulated horseradish peroxidase in a packed bed reactor system

In this study, horseradish peroxidase (HRP) was immobilized onto chitosan beads by entrapment method and employed for the degradation of textile dyes. Stable and firm quality chitosan beads developed with 2.5% chitosan concentration exhibited maximum immobilization yield (~92.54±2.53%). The pH optimum of chitosan-immobilized HRP (CTS-HRP) was marginally displaced towards alkaline region (pH7.5) than that of F-HRP which displayed its optimum activity at pH7.0. The free HRP (F-HRP) and CTS-HRP enzyme presented their maximum catalytic activities at 30°C and 70°C, respectively. Relative activities of F-HRP and CTS-HRP were decreased following pre-incubation above 30°C and 50°C, respectively and after 120min at 70°C, the F-HRP, and CTS-HRP retained 19.3±1.3 and 48.3±2.4% activities, accordingly. The CTS-HRP exhibited remarkably better resistance towards heavy metal induced activity inhibition. The effect of potential inhibitors on the activity of F-HRP and CTS-HRP was investigated and found that CTS-HRP was significantly less vulnerable to the denaturation caused by urea, ethylenediaminetetraacetic acid (EDTA), cysteine, 1, 4-dithiothreitol and Triton X-100. Moreover, the CTS-assisted entrapped-HRP was also employed for the decolorization of four different textile dyes i.e. Remazol Brilliant Blue R (RBBR), Reactive Black 5 (RB5), Congo Red (CR) and Crystal Violet (CV). The CTS-HRP showed considerable decolorization efficacy in six consecutive batch operations. Results suggest that CTS-HRP is an attractive choice for use as industrial biocatalyst in larger scale bioremediation of textile dyes and effluents.

Horseradish peroxidase inactivation: heme destruction and influence of polyethylene glycol

Horseradish peroxidase (HRP) mediates efficient conversion of many phenolic contaminants and thus has potential applications for pollution control. Such potentially important applications suffer however from the fact that the enzyme becomes quickly inactivated during phenol oxidation and polymerization. The work here provides the first experimental data of heme consumption and iron releases to support the hypothesis that HRP is inactivated by heme destruction. Product of heme destruction is identified using liquid chromatography with mass spectrometry. The heme macrocycle destruction involving deprivation of the heme iron and oxidation of the 4-vinyl group in heme occurs as a result of the reaction. We also demonstrated that heme consumption and iron releases resulting from HRP destruction are largely reduced in the presence of polyethylene glycol (PEG), providing the first evidence to indicate that heme destruction is effectively suppressed by co-dissolved PEG. These findings advance a better understanding of the mechanisms of HRP inactivation.

Immobilization of horseradish peroxidase by electrospun fibrous membranes for adsorption and degradation of pentachlorophenol in water

Horseradish peroxidase (HRP) is successfully in situ encapsulated into the poly(D,L-lactide-co-glycolide) (PLGA)/PEO-PPO-PEO (F108) electrospun fibrous membranes (EFMs) by emulsion electrospinning. The adsorption and degradation of pentachlorophenol (PCP) by HRP-EFMs are investigated. The experimental results show that the sorption kinetic of PCP on EFMs follows the pseudo-second-order model, and the sorption capacity is as high as 44.69 mg g(-1). The sorption mechanisms of EFMs for PCP can be explained by hydrogen bonding interactions, hydrophobic interactions and π-π bonding interactions. Profiting from the strong adsorption, the removal of PCP can be dramatically enhanced by the interaction of adsorbed PCP and HRP on the surface of EFMs. For PCP degradation, the optimal pH values for free HRP and immobilized HRP are 4 and 2-4, respectively. As pH>4.7, no adsorption and degradation are observed due to the deprotonation of PCP. The removal percentages reach 83% and 47% for immobilized HRP and free HRP, respectively, at 25 ± 1°C. The presence of humic acid can inhibit the activity of HRP and decreases the adsorption capacity of PCP because of competitive adsorption. The operational and storage stability of immobilized HRP are highly improved through emulsion electrospinning.

Degradation of pentachlorophenol by a novel peroxidase-catalyzed process in the presence of reduced nicotinamide adenine dinucleotide

A novel horseradish peroxidase (HRP)-catalyzed H₂O₂ process in the presence of reduced nicotinamide adenine dinucleotide (NADH) was applied to remove aqueous pentachlorophenol (PCP). Parameters (pH, H₂O₂ concentration, HRP activity and NADH dosage) on PCP removal were investigated. It was found that initial 0.05mM PCP was removed by 98% in HRP-NADH-H₂O₂ system at pH 5.0 and 30°C for 1h. Addition of O₂ in HRP-NADH-H₂O₂ system enhanced the removal rate of PCP due to promoting hydroxyl radicals (.OH) and superoxide anion radical (.O₂⁻) generation, which were confirmed by electron paramagnetic resonance (EPR)-spin trapping method. PCP removal efficiency decreased when .O₂⁻ and H₂O₂ were scavenged by superoxide dismutase and catalase in HRP-NADH-O₂ system, indicating that .OH/.O₂⁻ played a great role in the degradation of PCP. Gas chromatography-mass spectrometry (GC-MS) analysis revealed that octachlorinated dibenzodioxin (OCDD) in residual solution was reduced after treated by the HRP-NADH-O₂ process, resulting in lower toxicity of treated solution than conventional enzymatic process. Two enzymatic-catalysis pathways were proposed for PCP removal in HRP-NADH-H₂O₂/O₂ system: (i) OH/.O₂⁻ free radical oxidation (ii) conventional phenoxy polymerization.

Catalase-like activity of bovine met-hemoglobin: interaction with the pseudo-catalytic peroxidation of anthracene traces in aqueous medium

Hemoglobin is a member of the hemoprotein superfamily whose main role is to transport O(2) in vertebrate organisms. It has two known promiscuous enzymatic activities, peroxidase and oxygenase. Here we show for the first time that bovine hemoglobin also presents a catalase-like activity characterized by a V(max )of 344 microM/min, a K(M )of 24 mM and a k(cat) equal to 115/min. For high anthracene and hemoglobin concentrations and low hydrogen peroxide concentrations, this activity inhibits the expected oxidation of anthracene, which occurs through a peroxidase-like mechanism. Anthracene belongs to the polycyclic aromatic hydrocarbon (PAH) family whose members are carcinogenic and persistent pollutants found in industrial waste waters. Our results show that anthracene oxidation by hemoglobin and hydrogen peroxide follows a typical bi-bi ping-pong mechanism with a V(max) equal to 0.250 microM/min, K(M(H2O2) )of 80 microM, K(M(ANT)) of 1.1 microM and k(cat) of 0.17/min. The oxidation of anthracene is shown to be pseudo-catalytic because an excess of hemoglobin and hydrogen peroxide is required to make PAH completely disappear. Thus, bovine hemoglobin presents, in different degrees, all the catalytic activities of the hemoprotein group, which makes it a very interesting protein for biotechnological processes and one with which structure-activity relationships can be studied.

Chloroperoxidase-mediated transformation of highly halogenated monoaromatic compounds

Peroxidase transformations of widely distributed pollutants, tetra- and penta-chlorinated phenols and anilines, were studied using different peroxidases. Chloroperoxidase from Caldariomyces fumago was able to transform tetra- and penta-chlorinated phenols and anilines, while horseradish peroxidase, lignin peroxidase from Phanerochaete chrysosporium and versatile peroxidase from Bjerkandera adusta were able only to transform the halogenated phenols. Chloroperoxidase showed a specific activity on pentachlorophenol two orders of magnitude higher than lignin peroxidase and horseradish peroxidase, and one order of magnitude higher than versatile peroxidase. The main product from peroxidase oxidation in all cases was a polymeric and insoluble material. The insolubilization of halogenated phenols and anilines permits their removal, reduces their bioavailability, and thus reduces their environmental impact. The other minor products from the enzymatic transformation of highly chlorinated compounds were determined by mass spectrometry. Tetrachloroquinone, dimers and trimers of halogenated compounds were also identified. Chloroperoxidase was able to halogenate tetrachloroaniline to form pentachloroaniline.

Kinetic modelling of phenol co-oxidation using horseradish peroxidase

Phenol is an industrial pollutant and its removal from industrial wastewaters is of great importance. In order to design optimised phenol removal procedures by using horseradish peroxidase-based systems, there are some points that have to be dealt with. One of the most important issues is the need for reliable kinetics as this is one of the difficulties found during process scale-up. Although simplified kinetics can be used for limited ranges of operating conditions, they are not usually reliable for the description of varying process conditions. The present work describes the implementation of a kinetic model, based on a mechanism, for the co-oxidation of phenol and 4-aminoantipyrine (Am-NH2), which is used as a chromogen agent, with hydrogen peroxide as the oxidant. The model covers not only the variation of the concentrations of all the species involved, but also the effect of temperature in the reaction. The estimation of kinetic rate constants and activation energies for the various steps in the mechanism is performed with a single optimisation procedure, and all the experimental results are described using a unique set of parameters, which, thus, is valid over an extended range of operating conditions. The mechanism allowed the determination of a reliable kinetic model which is appropriate for the range of experimental conditions used. The computational model was also tested with an independent set of experiments with different conditions from the ones for which the parameters were estimated.