Thermally induced conformational changes in horseradish peroxidase

Assessing the Influence of Betaine-Based Natural Deep Eutectic Systems on Horseradish Peroxidase

To validate the use of horseradish peroxidase (HRP) in natural deep eutectic systems (NADES), five different betaine-based NADES were characterized in terms of water content, water activity, density, and viscosity experimentally and by thermodynamic modeling. The results show that the NADES under study have a water activity of about 0.4 at 37 °C for water contents between 14 and 22 wt %. The densities of the studied NADES had values between 1.2 and 1.3 g^.cm^-3 at 20 °C. The density was modeled with a state-of-the-art equation of state; an excellent agreement with the experimental density data was achieved, allowing reasonable predictions for water activities. The system betaine:glycerol (1:2) was found to be the most viscous with a dynamic viscosity of ∼600 mPa^.s at 40 °C, while all the other systems had viscosities <350 mPa^.s at 40 °C. The impact of the NADES on the enzymatic activity, as well as on, conformational and thermal stability was assessed. The system betaine/sorbitol:water (1:1:3) showed the highest benefit for enzymatic activity, increasing it by two-folds. Moreover, upon NADES addition, thermal stability was increased followed by an increment in a-helix secondary structure content.

CRISPR/Cas12a-based fluorescence immunoassay: combination of efficient signal generation with specific molecule recognition

The sensing strategy ingeniously combines the efficient signal generation of the CRISPR/Cas12a system with antigen–antibody-specific recognition.

Immobilizing Enzymes on Noble Metal Hydrogel Nanozymes with Synergistically Enhanced Peroxidase Activity for Ultrasensitive Immunoassays by Cascade Signal Amplification

Enzyme immobilization plays an essential role in solving the problems of the inherently fragile nature of enzymes. Although prominent stability and reuse of enzymes can be achieved by enzyme immobilization, their bioactivity and catalytic efficiency will be adversely affected. Herein, PdCu hydrogel nanozymes with a hierarchically porous structure were used to immobilize horseradish peroxidase (HRP) to obtain PdCu@HRP. In addition to the improvement of stability and reusability, PdCu@HRP displayed synergistically enhanced activities than native HRP and PdCu hydrogels. Not only the specific interactions between PdCu hydrogel nanozymes and enzymes but also the enrichment of substrates around enzymes by electrostatic adsorption of hydrogels was proposed to expound the enhanced catalytic activity. Accordingly, by taking advantage of the excellent catalytic performance of the PdCu@HRP and the glucose oxidase encapsulated in zeolitic imidazolate framework-8, colorimetric biosensing of the carcinoembryonic antigen via catalytic cascade reactions for achieving signal amplification was performed. The obtained biosensor enhanced the detection sensitivity by approximately 6.1-fold as compared to the conventional HRP-based enzyme-linked immunosorbent assay, demonstrating the promising potential in clinical diagnosis.

Adsorption of Horseradish Peroxidase on Metallic Nanoparticles: Effects on Reactive Oxygen Species Detection Using 2',7'-Dichlorofluorescin Diacetate

The fluorescent probe 2',7'-dichlorofluorescein diacetate (DCFH-DA) together with the enzyme horseradish peroxidase (HRP) is widely used in nanotoxicology to study acellular reactive oxygen species (ROS) production from nanoparticles (NPs). This study examined whether HRP adsorbs onto NPs of Mn, Ni, and Cu and if this surface process influences the extent of metal release and hence the ROS production measurements using the DCFH assay in phosphate buffered saline (PBS), saline, or Dulbecco's modified Eagle's medium (DMEM). Adsorption of HRP was evident onto all NPs and conditions, except for Mn NPs in PBS. The presence of HRP resulted in an increased release of copper from the Cu NPs in PBS and reduced levels of nickel from the Ni NPs in saline. Both metal ions in solution and the adsorption of HRP onto the NPs can change the activity of HRP and thus influence the ROS results. The effect of HRP on the NP reactivity was shown to be solution chemistry dependent. Most notable was the evident affinity/adsorption of phosphate toward the metal NPs, followed by a reduced adsorption of HRP, the concomitant reduction in released manganese from the Mn NPs, and increased levels of released metals from the Cu NPs in PBS. Minor effects were observed for the Ni NPs. The solution pH should be monitored since the release of metals can change the solution pH and the activity of HRP is known to be pH-dependent. It is furthermore essential that solution pH adjustments are made following the addition of NaOH during diacetyl removal of DCFH-DA. Even though not observed for the given exposure conditions of this study, released metal ions could possibly induce agglomeration or partial denaturation of HRP, which in turn could result in steric hindrance for H2O2 to reach the active site of HRP. This study further emphasizes the influence of HRP on the background kinetics, its solution dependence, and effects on measured ROS signals. Different ways of correcting for the background are highlighted, as this can result in different interpretations of generated results. The results show that adsorption of HRP onto the metal NPs influenced the extent of metal release and may, depending on the investigated system, result in either under- or overestimated ROS signals if used together with the DCFH assay. HRP should hence be used with caution when measuring ROS in the presence of reactive metallic NPs.

Computational Investigation of Protein Photoinactivation by Molecular Hyperthermia

To precisely control protein activity in a living system is a challenging yet long-pursued objective in biomedical sciences. Recently, we have developed a new approach named molecular hyperthermia (MH) to photoinactivate protein activity of interest without genetic modification. MH utilizes nanosecond laser pulse to create nanoscale heating around plasmonic nanoparticles to inactivate adjacent protein in live cells. Here we use a numerical model to study important parameters and conditions for MH to efficiently inactivate proteins in nanoscale. To quantify the protein inactivation process, the impact zone is defined as the range where proteins are inactivated by the nanoparticle localized heating. Factors that reduce the MH impact zone include the laser pulse duration, temperature-dependent thermal conductivity (versus constant properties), and nonspherical nanoparticle geometry. In contrast, the impact zone is insensitive to temperature-dependent material density and specific heat, as well as thermal interface resistance based on reported data in the literature. The low thermal conductivity of cytoplasm increases the impact zone. Different proteins with various Arrhenius kinetic parameters have significantly different impact zones. This study provides guidelines to design the protein inactivation process by MH.

Studies on peroxidase from Moringa oleifera Lam leaves

Kinetic and physicochemical properties of Moringa oleifera peroxidase purified using a novel and cost efficient protocol was investigated with a view to providing information on its possible biotechnological potentials. Moringa oleifera peroxidase was purified to homogeneity in two steps, involving ATPS and size exclusion chromatography on Sephadex G-100 with a yield of 84.12 %. In-gel activity staining revealed the presence of one isoform of peroxidase. The purified peroxidase is monomeric with native and subunits molecular weight of 38.9 and 43.5 kDa respectively. Kinetic parameters - V _max, K _m(app) ^{o-dianisidine}, K _m(app) ^H ₂ ^O ₂ of the purified enzyme were 2.5 units/mg protein, 0.020 ± 0.04 mM and 1.37 ± 0.18 mM respectively. Its optimum pH and temperature were 5 and 30 °C respectively. The purified enzyme cross-linked BSA into an insoluble matrix with the aid of caffeic acid. The study concluded that the purification scheme adopted is rapid and efficient, the purified enzyme exhibited some physiochemical properties that make it suitable for various biotechnological applications.

Antibody-Electroactive Probe Conjugates Based Electrochemical Immunosensors

Suitable immobilization of a biorecognition element, such as an antigen or antibody, on a transducer surface is essential for development of sensitive and analytically reliable immunosensors. In this review, we report on (1) methods of antibody prefunctionalization using electroactive probes, (2) methods for immobilization of such conjugates on the surfaces of electrodes in electrochemical immunosensor construction and (3) the use of antibody-electroactive probe conjugates as bioreceptors and sensor signal generators. We focus on different strategies of antibody functionalization using the redox active probes ferrocene (Fc), anthraquinone (AQ), thionine (Thi), cobalt(III) bipyridine (Co(bpy)33+), Ru(bpy)32+ and horseradish peroxidase (HRP). In addition, new possibilities for antibody functionalization based on bioconjugation techniques are presented. We discuss strategies of specific, quantitative antigen detection based on (i) a sandwich format and (ii) a direct signal generation scheme. Further, the integration of different nanomaterials in the construction of these immunosensors is presented. Lastly, we report the use of a redox probe strategy in multiplexed analyte detection.

Non-Arrhenius Reaction-Diffusion Kinetics for Protein Inactivation over a Large Temperature Range

Understanding protein folding and unfolding has been a long-standing fundamental question and has important applications in manipulating protein activity in biological systems. Experimental investigations of protein unfolding have been predominately conducted by small temperature perturbations (e.g., temperature jump), while molecular simulations are limited to small time scales (microseconds) and high temperatures to observe unfolding. Thus, it remains unclear how fast a protein unfolds irreversibly and loses function (i.e., inactivation) across a large temperature range. In this work, using nanosecond pulsed heating of individual plasmonic nanoparticles to create precise localized heating, we examine the protein inactivation kinetics at extremely high temperatures. Connecting this with protein inactivation measurements at low temperatures, we observe that the kinetics of protein unfolding is less sensitive to temperature change at the higher temperatures, which significantly departs from the Arrhenius behavior extrapolated from low temperatures. To account for this effect, we propose a reaction-diffusion model that modifies the temperature-dependence of protein inactivation by introducing a diffusion limit. Analysis of the reaction-diffusion model provides general guidelines in the behavior of protein inactivation (reaction-limited, transition, diffusion-limited) across a large temperature range from physiological temperature to extremely high temperatures. We further demonstrate that the reaction-diffusion model is particularly useful for designing optimal operating conditions for protein photoinactivation. The experimentally validated reaction-diffusion kinetics of protein unfolding is an important step toward understanding protein-inactivation kinetics over a large temperature range. It has important applications including molecular hyperthermia and calls for future studies to examine this model for other protein molecules.

Optimization of Horseradish Peroxidase Catalytic Degradation for 2-Methyl-6-Ethylaniline Removal Using Response Surface Methodology

For optimizing the reaction conditions of 2-methyl-6-ethylaniline (MEA) degradation catalyzed by horseradish peroxidase (HRP), a response surface methodology with three factors and three levels was used in this research to establish a regression model, a ternary quadratic polynomial, in order to analyze temperature, H2O2 concentration and pH effects on MEA removal efficiency. The results showed that the regression model was significant (p < 0.0001), fitted well with experimental data and had a high degree of reliability and accuracy, and the data were reasonable with low errors. By analyzing interactions and solving the regression model, the maximum MEA removal efficiency was 97.90%, and the optimal conditions were defined as follows: pH 5.02, H2O2 concentration 13.41mM, and temperature 30.95 °C. Under the optimal conditions, the average MEA removal efficiency obtained from the experiments was 97.56%. This research can provide reference for the treatment of actual acetochlor industrial wastewater.

An efficient methodology for the purification of date palm peroxidase: Stability comparison with horseradish peroxidase (HRP)

In the present study, Peroxidase from date palm (Phoenix dactylifera) leaves was purified to homogeneity by three-step procedure including aqueous two-phase system, hydrophobic and Ion-exchange chromatography. The enzyme migrated as single band on SDS-PAGE giving molecular weight of 68 ± 3 kDa. The purification factor for purified date palm peroxidase was 68 with high 41% yield. Enzymatic assays together with far-UV circular dichroism (CD), intrinsic and extrinsic fluorescence studies were carried out to monitor the structural stability of date palm and horseradish peroxidase (HRP) against various pH and temperatures. Activity measurements illustrated different pH stability for date palm and HRP. Both peroxidases are more susceptible to extreme acidic conditions as suggested by 4 & 15 nm red shift in date palm and HRP, respectively. Secondary structure analysis using far UV-CD exhibited predominance of α-helical (43.8%) structure. Also, pH induces loss in the secondary structure of date palm peroxidase. Thermal stability analysis revealed date palm peroxidase is more stable in comparison to HRP. In summary, date palm peroxidases could be promising enzymes for various applications where extreme pH and temperature is required.

Improving the thermal stability of azoreductase from Halomonas elongata by introducing a disulfide bond via site-directed mutagenesis

Azoreductases mainly reduce azo dyes, the largest class of colorants, to colorless aromatic amines. AzoH, a new azoreductase from the halophilic bacterium, Halomonas elongata, has been recently cloned and expressed in Escherichia coli. The aim of this study was to improve thermal stability of this enzyme by introducing new disulfide bonds. Since X-ray crystallography was not available, homology modeling and molecular dynamics was used to construct the enzyme three-dimensional structure. Potential disulfide bonds for increasing thermal stability were found using DIScover online software. Appropriate mutations (L49C/D108C) to form a disulfide bond were introduced by the Quik-Change method. Mutant protein expressed in E. coli showed increased thermal stability at 50 °C (increased half-life from 12.6 Min in AzoH to 26.66 Min in a mutated enzyme). The mutated enzyme could also tolerate 5% (w/v) NaCl and retained 30% of original activity after 24 H incubation, whereas the wild-type enzyme was completely inactivated. According to circular dichroism studies, the secondary structure was not altered by this mutation; however, a blue shift in intrinsic florescent graph revealed changes in the tertiary structure. This is the first study to improve thermal stability and salt tolerance of a halophilic azoreductase.

Influence of Surface Charge of the Nanostructures on the Biocatalytic Activity

The physicochemical properties of abiotic nanostructures determine the structure and function of biological counterparts in biotic-abiotic nanohybrids. A comprehensive understanding of the interfacial interactions and the predictive capability of their structure and function is paramount for virtually all fields of bionanotechnology. In this study, using plasmonic nanostructures as a model abiotic system, we investigate the effect of the surface charge of nanostructures on the biocatalytic reaction kinetics of a bound enzyme. We found that the surface charge of nanostructures profoundly influences the structure, orientation, and activity of the bound enzyme. Furthermore, the interactions of the enzyme with nanoparticles result in stable conjugates that retain their functionality at elevated temperatures, unlike their free counterparts that lose their secondary structure and biocatalytic activity.

Time-resolved fluorescence observation of di-tyrosine formation in horseradish peroxidase upon ultrasound treatment leading to enzyme inactivation

The application of ultrasound to a solution can induce cavitional phenomena and generate high localised temperatures and pressures. These are dependent of the frequency used and have enabled ultrasound application in areas such as synthetic, green and food chemistry. High frequency (100kHz to 1MHz) in particular is promising in food chemistry as a means to inactivate enzymes, replacing the need to use periods of high temperature. A plant enzyme, horseradish peroxidase, was studied using time-resolved fluorescence techniques as a means to assess the effect of high frequency (378kHz and 583kHz) ultrasound treatment at equivalent acoustic powers. This uncovered the fluorescence emission from a newly formed species, attributed to the formation of di-tyrosine within the horseradish peroxidase structure caused by auto-oxidation, and linked to enzyme inactivation.

Peculiarities of thermal denaturation of OmpF porin from Yersinia ruckeri

Irreversible denaturation of membrane proteins in detergent solutions is similar to unfolding of water-soluble multidomain proteins and represents a complex, multistage process.

Irreversible denaturation of maltodextrin glucosidase studied by differential scanning calorimetry, circular dichroism, and turbidity measurements

Thermal denaturation of Escherichia coli maltodextrin glucosidase was studied by differential scanning calorimetry, circular dichroism (230 nm), and UV-absorption measurements (340 nm), which were respectively used to monitor heat absorption, conformational unfolding, and the production of solution turbidity. The denaturation was irreversible, and the thermal transition recorded at scan rates of 0.5–1.5 K/min was significantly scan-rate dependent, indicating that the thermal denaturation was kinetically controlled. The absence of a protein-concentration effect on the thermal transition indicated that the denaturation was rate-limited by a mono-molecular process. From the analysis of the calorimetric thermograms, a one-step irreversible model well represented the thermal denaturation of the protein. The calorimetrically observed thermal transitions showed excellent coincidence with the turbidity transitions monitored by UV-absorption as well as with the unfolding transitions monitored by circular dichroism. The thermal denaturation of the protein was thus rate-limited by conformational unfolding, which was followed by a rapid irreversible formation of aggregates that produced the solution turbidity. It is thus important to note that the absence of the protein-concentration effect on the irreversible thermal denaturation does not necessarily means the absence of protein aggregation itself. The turbidity measurements together with differential scanning calorimetry in the irreversible thermal denaturation of the protein provided a very effective approach for understanding the mechanisms of the irreversible denaturation. The Arrhenius-equation parameters obtained from analysis of the thermal denaturation were compared with those of other proteins that have been reported to show the one-step irreversible thermal denaturation. Maltodextrin glucosidase had sufficiently high kinetic stability with a half-life of 68 days at a physiological temperature (37°C).

Ternary interpolyelectrolyte complexes insulin-poly(methylaminophosphazene)-dextran sulfate for oral delivery of insulin

Ternary interpolyelectrolyte complexes of insulin with biodegradable synthetic cationic polymer, poly(methylaminophosphazene) hydrochloride (PMAP), and dextran sulfate (DS) were investigated by means of turbidimetry, dynamic light scattering, phase analysis, and high-sensitivity differential scanning calorimetry. Formation of ternary insoluble stoichiometric Insulin-PMAP-DS complexes was detected under conditions imitating the human gastric environment (pH 2, 0.15 M NaCl). A complete immobilization of insulin in the complexes was observed in a wide range of the reaction mixture compositions. The ternary complexes were shown to dissolve and dissociate under conditions imitating the human intestinal environment (pH 8.3, 0.15 M NaCl). The products of the complex dissociation were free insulin and soluble binary Insulin-PMAP complexes. The conformational stability of insulin in the soluble complexes of various compositions was investigated by high-sensitivity differential scanning calorimetry. The dependence of the excess denaturation free energy of insulin in these complexes on the PMAP content was obtained. The binding constants of the folded and unfolded forms of insulin to the PMAP polycation were estimated. Proteolysis of insulin involved in the insoluble ternary complexes by pepsin was investigated under physiological conditions. It was found that the complexes ensure an almost 100% protection of insulin against proteolytic degradation. The obtained results provide a perspective basis for development of oral insulin preparations.

Effect of low molecular weight additives on immobilization strength, activity, and conformation of protein immobilized on PVC and UHMWPE

Horseradish peroxidase (HRP) was immobilized onto both plasticized and unplasticized polyvinylchloride (PVC) and ultrahigh molecular weight polyethylene (UHMWPE). Plasma immersion ion implantation (PIII) in a nitrogen plasma with 20 kV bias was used to facilitate covalent immobilization and to improve the wettability of the surfaces. The surfaces and immobilized protein were studied using attenuated total reflection infrared (ATR-IR) spectroscopy and water contact angle measurements. Protein elution on exposure to repeated sodium dodecyl sulfate (SDS) washing was used to assess the strength of HRP immobilization. The presence of low molecular weight components (plasticizer, additives in solvent, unreacted monomers, adsorbed molecules on surface) was found to have a major influence on the strength of immobilization and the conformation of the protein on the samples not exposed to the PIII treatment. A phenomenological model considering interactions between the low molecular weight components, the protein molecule, and the surface is developed to explain these observations.

Investigating the structural and functional effects of mutating Asn glycosylation sites of horseradish peroxidase to Asp

Horseradish peroxidase (HRP) has long attracted intense research interest and is used in many biotechnological fields, including diagnostics, biosensors, and biocatalysis. Enhancement of HRP catalytic activity and/or stability would further increase its applications. One of the problems with heterologus expression of HRP especially in prokaryotic host is lack of glycosylation that affects it's stability toward H(2)O(2) and thermal inactivation. In this study, two asparagine residues which constitute two of the eight glycosylation sites in native HRP (Asn 13 and 268) with respectively 83% and 65% surface accessibility were substituted with aspartic acid in recombinant HRP. Both mutant proteins expressed in Escherichia coli showed increased stabilities against heat (increase in t (1/2) from 20 min in native rHRP to 32 and 67 min in N13D and N268D) and H(2)O(2) (up to threefold). Unexpectedly, despite the distance of the mutated positions from the active site, notable alterations in steady-state k (cat) and K (m) values occurred with phenol/4-aminoantipyrine as reducing substrate which might be due to conformational changes. No significant alteration in flexibility was detected by acrylamide quenching analyses, but ANS binding experiments purposed lesser binding of ANS to hydrophobic patches in mutated HRPs. Double mutation was non-additive and non-synergistic.

Immunosensor based on fluorescence quenching matrix of the conducting polymer polypyrrole

In this study, the combination of autofluorescent proteins and fluorescence quenching polymers was shown to be a design which can increase the selectivity and sensitivity of immunosensors. With this objective, the conducting polymer polypyrrole (Ppy) was used as a matrix for immobilization of proteins, which enables biological recognition of the analyte, and as a fluorescence quencher, which increases the selectivity of fluorescence-based detection. In this study, bovine leukemia virus proteins gp51 were immobilized within the Ppy matrix and formed a polymeric layer with affinity for antibodies against protein gp51 (anti-gp51). The anti-gp51 antibodies are present at high levels in the blood serum of cattle infected by bovine leukemia virus. Secondary antibodies labeled with horseradish peroxidase (HRP) were used as specific fluorescent probes for detection of a particular target, because the fluorescence of HRP was readily detectable at the required sensitivity. The Ppy was used as fluorescent background, because its fluorescence was almost undetectable when excited by near UV light at 325 nm. Moreover the Ppy quenched the fluorescence of some fluorescent agents including fluorescein-5(6)-isothiocyanate (fluorescein), rhodamine B, and HRP by almost 100% when these fluorescent agents were adsorbed on the surface of Ppy. It is predicted that Ppy-induced fluorescence quenching could be used in the design of immunosensors to increase selectivity and sensitivity.

Differential scanning calorimetry and fluorescence study of lactoperoxidase as a function of guanidinium-HCl, urea, and pH

The stability of bovine lactoperoxidase to denaturation by guanidinium-HCl, urea, or high temperature was examined by differential scanning calorimetry (DSC) and tryptophan fluorescence. The calorimetric scans were observed to be dependent on the heating scan rate, indicating that lactoperoxidase stability at temperatures near Tm is controlled by kinetics. The values for the thermal transition, Tm, at slow heating scan rate were 66.8, 61.1, and 47.2 degrees C in the presence of 0.5, 1, and 2 M guanidinium-HCl, respectively. The extrapolated value for Tm in the absence of guanidinium-HCl is 73.7 degrees C, compared with 70.2 degrees C obtained by experiment; a lower experimental value without a denaturant is consistent with distortion of the thermal profile due to aggregation or other irreversible phenomenon. Values for the heat capacity, Cp, at Tm and Ea for the thermal transition decrease under conditions where Tm is lowered. At a given concentration, urea is less effective than guanidinium-HCl in reducing Tm, but urea reduces Cp relatively more. Both fluorescence and DSC indicate that thermally denatured protein is not random coil. A change in fluorescence around 35 degrees C, which was previously reported for EPR and CD measurements (Boscolo et al. Biochim. Biophys. Acta 1774 (2007) 1164-1172), is not seen by calorimetry, suggesting that a local and not a global change in protein conformation produces this fluorescence change.

Stabilization of horseradish peroxidase by covalent conjugation with dextran aldehyde against temperature and pH changes

Stabilization of Horseradish Peroxidase (HRP; EC 1.11.1.7) against temperature and pH via the formation of the conjugates obtained by multipoint covalent bonding of dextran aldehyde (DA) to the enzyme were studied. Hence, three different molar weighted dextrans (17.5 kD, 75 kD, 188 kD) were covalently bonded to purified enzyme with different molar ratios (nHRP/nDA 20/1, 10/1, 1/1, 1/5, 1/10, 1/15, 1/20). The thermal stabilities of the obtained conjugates were evaluated with the activities determined at different temperatures (25, 30, 35, 40, 50, 60, 70, 80°C) applying 60 minutes incubation time. Conjugates formed were characterized by gel-permeation chromatography (GPC) and fluorescence techniques. The conjugate synthesized using dextran 75 kDa with nHRP/nDA 1/10 molar ratio showed better thermal stability than other conjugates and purified enzyme at pH 7. This conjugate also has wider activity pH range than purified enzyme. In addition, mentioned conjugate at pH 7 had very long storage lifetime compared to purified enzyme at +4°C and room temperature; which is considered a favorable feature for usage in practice.

Detoxification of simulated textile wastewater using a membraneless electrochemical reactor with immobilized peroxidase

Simulated textile wastewater was degraded using a membraneless electrochemical reactor with immobilized peroxidase on the porous Celite. The optimal current density was 10 A m(-2), at which the highest amount of hydrogen (H(2)O(2)) could be generated. The decolorization efficiencies of the simulated wastewater using the electrochemical and electroenzymatic methods were 35% and 92%, respectively. Biodegradability, the ratio of 5-day biochemical oxygen demand to chemical oxygen demand (BOD(5)/COD), was enhanced about 1.88 times when using the electroenzymatic treatment rather than raw wastewater, which could not be achieved by the electrochemical treatment. The toxic unit (TU), calculated using the lethal concentration (LC(50)) of Daphnia magna (D. Magna), of effluent treated by electroenzymatic method was below 1, whereas those of simulated textile wastewater and effluent treated by electrochemical method were 11.4 and 3.9, respectively.

Thermal stability of peroxidase from Chamaerops excelsa palm tree at pH 3

The structural stability of a peroxidase, a dimeric protein from palm tree Chamaerops excelsa leaves (CEP), has been characterized by high-sensitivity differential scanning calorimetry, circular dichroism and steady-state tryptophan fluorescence at pH 3. The thermally induced denaturation of CEP at this pH value is irreversible and strongly dependent upon the scan rate, suggesting that this process is under kinetic control. Moreover, thermally induced transitions at this pH value are dependent on the protein concentration, leading to the conclusion that in solution CEP behaves as dimer, which undergoes thermal denaturation coupled with dissociation. Analysis of the kinetic parameters of CEP denaturation at pH 3 was accomplished on the basis of the simple kinetic scheme N-->kD, where k is a first-order kinetic constant that changes with temperature, as given by the Arrhenius equation; N is the native state, and D is the denatured state, and thermodynamic information was obtained by extrapolation of the kinetic transition parameters to an infinite heating rate.

Effects of mutations in the helix G region of horseradish peroxidase

Horseradish peroxidase (HRP) has long attracted intense research interest and is used in many biotechnological fields, including diagnostics, biosensors and biocatalysis. Enhancement of HRP catalytic activity and/or stability would further increase its usefulness. Based on prior art, we substituted solvent-exposed lysine and glutamic acid residues near the proximal helix G (Lys 232, 241; Glu 238, 239) and between helices F and F' (Lys 174). Three single mutants (K232N, K232F, K241N) demonstrated increased stabilities against heat (up to 2-fold) and solvents (up to 4-fold). Stability gains are likely due to improved hydrogen bonding and space-fill characteristics introduced by the relevant substitution. Two double mutants showed stability gains but most double mutations were non-additive and non-synergistic. Substitutions of Lys 174 or Glu 238 were destabilising. Unexpectedly, notable alterations in steady-state Vm/E values occurred with reducing substrate ABTS (2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid)), despite the distance of the mutated positions from the active site.

Thermostability, solvent tolerance, catalytic activity and conformation of cofactor modified horseradish peroxidase

Artificial prosthetic groups, HeminD1 and HeminD2, were designed and synthesized, which contain one benzene ring and one carboxylic group or two carboxylic groups at the terminal of each propionate side chain of hemin, respectively. HeminD1 and HeminD2 were reconstituted with apo-HRP successfully to produce the two novel HRPs, rHRP1 and rHRP2, respectively. The thermal and solvent tolerances of native and reconstituted HRPs were compared. The cofactor modification increased the thermostability both in aqueous buffer and some organic solvents, and also enhanced the tolerance of some organic solvents. To determine the conformation stability, the unfolding of native and reconstituted HRPs by heat was investigated. Tm was increased from 70.0 degrees C of nHRP to 75.4 degrees C of rHRP1 and 76.5 degrees C of rHRP2 after cofactor modification. Kinetic studies indicated that the cofactor modification increased the substrate affinity and catalytic efficiency both in aqueous buffer and some organic solvents. The catalytic efficiency for phenol oxidation was increased by approximately 55% for rHRP1 in aqueous buffer, and it was also increased by approximately 70% for rHRP1 in 10% ACN. Spectroscopic studies proved that the cofactor modification changed the microenvironment of both heme and tryptophan, increased alpha-helix content, and increased the tertiary structure around the aromatic residue in HRP. The improvements of catalytic properties are related to these changes of the conformation. The introduction of the hydrophobic domain as well as the retention of the moderate carboxylic group in active site is an efficient method to improve the thermodynamic and catalytic efficiency of HRP.

Broccoli processing wastes as a source of peroxidase

A peroxidase isozyme (BP) was purified to homogeneity from broccoli stems ( Brassica oleraceae var. maraton) discarded from industrial processing wastes. BP specific activity was 1216 ABTS [2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid)] units/mg, representing 466-fold that of crude extract. BP is a monomeric glycoprotein containing 16% carbohydrates, with a molecular mass of 49 kDa and an isoelectric point close to 4.2. From kinetic data it showed a two-substrate ping-pong mechanism, and the catalytic efficiency measured as the rate-limiting step of free BP regeneration was 3.4 x 10(6) M(-1) s(-1). The ABTS K m value was 0.2 mM, which was about 20 times lower than that reported for acidic commercial horseradish peroxidase (HRP). Assessment of BP secondary structure showed 30% helical character, similar to HRP and cytochrome c peroxidase. BP lost only 25% activity after 10 min of heating at 55 degrees C and pH 6; it was stable in the pH range from 4 to 9 and showed an optimum pH of 4.6 using ABTS as substrate. BP was active on substrates normally involved in lignin biosynthesis, such as caffeic and ferulic acids, and also displayed good catechol oxidation activity in the presence of hydrogen peroxide. Reverse micellar extraction was successfully used as potential large-scale prepurification of broccoli peroxidase, achieving a purification factor of 7, with 60% activity yield. Stems from the broccoli processing industry have a high potential as an alternative for peroxidase purification.

Application of zero-length cross-linking to form lysozyme, horseradish peroxidase and lysozyme–peroxidase dimers: Activity and stability

A facile method for the formation of covalent bonds between protein molecules is zero-length cross-linking. This method enables the formation of cross-links without use of any chemical reagents. Here, the cross-linking is performed for lysozyme, peroxidase (a glycoprotein) and between lysozyme-peroxidase by the method of Simons et al. [B.L. Simons, M.C. King, T. Cyr, M.A. Hefford, H. Kaplan, Covalent cross-linking of protein without chemical reagents, Protein Sci. 2002, 11, 1558-1564]. Approximately one-third of the total lysozyme becomes cross-linked and the dimer form was the major product for both enzymes. This modification induced some changes in the kinetic properties of the dimer peroxidase, as evident by two-fold increasing of V(max) compared to the monomer but the enzymatic activity of cross-linked lysozyme dimer was the same as monomer. The activity of lysozyme dimer remained constant up to 10min at 80 degrees C, while peroxidase activity of both monomer and dimer began to decrease after heating. The structural changes of the enzymes were investigated by circular dichroism and intrinsic fluorescence techniques. Near UV result showed lysozyme possess a compact structure in the dimer form but disruption of tertiary structure of peroxidase dimer was observed. Also conformational changes were detected and discussed by intrinsic fluorescence experiments. Effect of several metals in the formation of lysozyme dimer showed that Co(2+) is the most effective one but its effect was marginal. At the end formation of heterogeneous dimer, peroxidase-lysozyme, was achieved using this method.

Role of copper in thermal stability of human ceruloplasmin

Human ceruloplasmin (CP) is a multicopper oxidase essential for normal iron homeostasis. The protein has six domains with one type-1 copper in each of domains 2, 4, and 6; the remaining coppers form a catalytic trinuclear cluster at the interface between domains 1 and 6. To assess the role of the coppers in CP thermal stability, we have probed the thermal unfolding process as a function of scan rate of holo- and apo-forms using several detection methods (circular dichroism, aromatic and 8-anilino-naphthalene-1-sulfonic acid fluorescence, visible absorption, activity, and differential scanning calorimetry). Both species of CP undergo irreversible thermal reactions to denatured states with significant residual structure. For identical scan rates, the thermal midpoint appears at temperatures 15-20 degrees higher for the holo- as compared with the apo- form. The thermal data for both forms were fit by a mechanistic model involving two consecutive, irreversible steps (N --> I --> D). The holo-intermediate, I, has lost one oxidized type-1 copper and secondary structure in at least one domain; however, the trinuclear copper cluster remains intact as it is functional in oxidase activity. The activation parameters obtained from the fits to the thermal transitions were used to assess the kinetic stability of apo- and holo-CP at physiological temperatures (i.e., at 37 degrees C). It emerges that native CP (i.e., with six coppers) is rather unstable and converts to I in <1 day at 37 degrees C. Nonetheless, this form remains intact for more than 2 weeks and may thus be a biologically relevant state of CP in vivo. In contrast, apo-CP unfolds rapidly: the denatured state is reached in <2 days at 37 degrees C.

The attachment of catalase and poly-l-lysine to plasma immersion ion implantation-treated polyethylene

Plasma immersion ion implantation (PIII) treatment of polyethylene increased the functional attachment of catalase and increased the retention of enzyme activity in comparison to untreated controls. The attached protein was not removed by SDS or NaOH, while that on the untreated surfaces was easily removed. Poly-l-lysine was found to attach in a similar way to the treated surface and could not be removed by NaOH, while it did not attach to the untreated surface. This indicates that a new binding mechanism, covalent in nature, is introduced by the plasma treatment. Surfaces treated with PIII maintained the catalase activity more effectively than surfaces plasma treated without PIII. The PIII-treated surface was hydrophilic compared to the untreated surface and retained its hydrophilic character better than surfaces subjected to a conventional plasma treatment process. The strong modification of a deeper region of the polymer than for conventional plasma treatments is believed to be responsible for both the enhanced hydrophilic character and for the increase in functional lifetime of the attached protein. The results show that PIII treatment of polymers increases their usefulness for protein microarrays.

Conducting polymer based fluorescence quenching as a new approach to increase the selectivity of immunosensors

Polypyrrole (Ppy) has been shown to be a superior matrix for fluorescence detection based immunosensors: (i) the fluorescence of polypyrrole and polypyrrole modified by entrapped proteins was almost not detectable when this polymer was excited by near UV 325 nm light; (ii) polypyrrole quenched the fluorescence of such fluorescence agents as fluoresceine 5(6)-isothiocyanate, rhodamine B and enzyme-horseradish peroxidase (HRP) by almost 100% if they were deposited in the solution as a drop at the Ppy surface followed by evaporation of the solvent. According to our knowledge, this work is first application of Ppy in the design of a fluorescence-based immunosensor, where low Ppy fluorescence background and Ppy induced fluorescence quenching were exploited. These sensors were devoted to the detection of antibodies against bovine leukemia virus (BLV) protein gp51 (anti-gp51-Ab). A biological recognition system of this fluorescence immunosensor model was based on polypyrrole with entrapped BLV proteins gp51 (gp51/Ppy). This gp51/Ppy layer was applied for the detection of anti-gp51-Ab. Secondary antibodies against anti-gp51-Ab labeled with HRP (Ab*) were applied as fluorescence-detectable labels that are able to recognize specifically and interact with the complex of gp51 proteins and anti-gp51-Ab antibodies (gp51/anti-gp51-Ab). It was demonstrated that fluorescence of non-specifically adsorbed Ab* was almost completely quenched by the Ppy substrate. In addition, enzymatic activity of HRP was exploited as a traditional reference method for verification of the formation of the immune complex gp51/anti-gp51-Ab/Ab*.