Enhanced intracellular stability of dextran-horse radish peroxidase conjugate: an approach to enzyme replacement therapy.

Horse radish peroxidase (HRP), a mannose-containing glycoprotein was covalently modified by conjugation with dextran. The rapid uptake of HRP by the liver is markedly inhibited by mannan. The uptake of dextran-HRP conjugate by the liver, though lower compared to that of the free enzyme, is also partially inhibited by mannan. Liposomes were therefore used as carriers for delivering the free and the modified HRP to the liver. The dextran-HRP conjugate showed greater stability intracellularly as compared to the free enzyme. The enhanced stability of enzymes upon their extensive glycosylation with nondegradable sugar polymers would be of importance in extending the catalytic life of therapeutically active enzymes and thereby improve their therapeutic potential for the treatment of certain enzyme deficiency disorders.     

Extracellular PH 2.5 optimum acid phosphatase from Aspergillus ficuum: immobilization on modified fractogel

Aspergillus ficuum pH 2.5 optimum acid phosphatase (orthophosphoric monoesters phosphohydrolase, E.C.3.1.3.2) was covalently immobolized on 2-fluoro-1-methylpyridinium toluene-4-sulfonate (FMP)-activated Fractogel TSK HW-50F. The catalytic parameters and stability of the immobilized enzyme were compared with those of the free enzyme. While the Km and the temperature optima were unchanged, the Ki for orthophosphate was changed from 185 microM to 422 microM and greater stability was observed against heat treatment.     

A bienzyme channeling glucose sensor with a wide concentration range based on co-entrapment of enzymes in SBA-15 mesopores

A novel bienzyme-channeling sensor was constructed by entrapping glucose oxidase (GOD) and horseradish peroxidase (HRP) in the mesopores of well-ordered hexagonal mesoporous silica structures (SBA-15). The SBA-15 mesoporous materials accelerated the electron transfer between the entrapped HRP and electrode. Both HRP and GOD retained their catalytic activities in the bienzyme-entrapped SBA-15 film. In presence of glucose the enzymatic reaction of GOD-glucose-dissolved oxygen system generated hydrogen peroxide in the bienzyme-entrapped mesopores, which was immediately reduced at -0.40 V by an electrocatalytic reaction with the HRP entrapped in the same mesopore to lead to a sensitive and fast amperometric response. Thus the bienzyme channeling could be used for the detection of glucose with excellent performance without the addition of any mediator. Optimization of the experimental parameters was performed with regard to pH, operating potential and temperature. The detection limit was down to 2.7 x 10(-7)M with a very wide linear range from 3.0 x 10(-6) to 3.4 x 10(-2)M. The constructed bienzyme channeling provided a strategy for amperometric detection of oxidase substrates by co-entrapping the corresponding oxidase and HRP in the mesoporous materials.     

Coimobilization of superoxide dismutase, catalase and peroxidase

For preparationing the polyenzyme antioxidant complex, containing superoxide dismutase (SOD), catalase and horseradish peroxidase (HRP), the different successivities of those enzymes co-immobilization were compared. The optimum successivity is provided by simultaneous co-immobilization of covalently bound HRP with the SOD and catalase. The catalytic enzyme activity and the catalase operational stability was kinetically characterized in various samples. For one sample, the influence of ascorbate, glutathione and ethanol on the catalase kinetic parameters was studied. A possible scheme of different processes at the H2O2 decomposition in the presence of co-immobilized SOD, catalase, HRP and the substrates-reductans was discussed.     

Preparation of photo-crosslinkable cinnamate modified hyaluronic acid for immobilization of horseradish peroxidase

In this work, a photo-responsive hydrogel membrane based on cinnamate-modified hyaluronic acid (HA-CM) was developed and safely cross-linked under UV light curing. The obtained material was effectively utilized for immobilization of horseradish peroxidase (HRP) enzyme via encapsulation and entrapment strategy with efficiency above 95%. The prepared HA-CM biopolymer was investigated before the UV curing using instrumental and spectral techniques including Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR). During the UV irradiation, the progress of the cross-linking reaction was monitored by the UV–vis light spectroscopy. In addition, when the photo-induced cross-linking had accomplished, the morphological appearance of the hydrogel membrane was recorded using a scanning electron microscope (SEM). The HRP immobilized in HA-CM membranes displayed remarkable stability against the environmental pH changes especially under alkaline media and shift the optimum pH to 8 compared to the free HRP, which exhibited the highest activity at pH 7. Also, the entrapped enzyme was able to preserve above 85% of its catalytic activity at higher temperature values where the free enzyme had deactivated by approximately 50%. Moreover, HA-CM-HRP maintained 87% of its activity after 10 sequential reuse cycles, which indicate the economic value of the employed immobilization strategy.     

Preparation and application of poly(N,N-dimethylacrylamide-co-acrylamide) and poly(N-isopropylacrylamide-co-acrylamide)/kappa-Carrageenan hydrogels for immobilization of lipase

In the present of this study, two novel polymeric matrixes that are poly(N,N-dimethylacrylamide-co-acrylamide) and poly(N-isopropylacrylamide-co-acrylamide)/kappa-Carrageenan was synthesized and applied for immobilization of lipase. For the immobilization of enzyme, two different immobilization procedures have been carried out via covalently binding and entrapment methods. On the free and immobilized enzymes activities, optimum pH, temperature, storage and thermal stability was investigated. The optimum temperature for free, covalently immobilized and entrapped enzymes was found to be 30, 35 and 30 degrees C, respectively. Optimum pH for both free and immobilized enzymes was also observed at pH 8. Maximum reaction rate (Vmax) and Michaelis-Menten constant (Km) were determined for free and immobilized lipases. Furthermore, the reuse numbers of immobilized enzymes also studied. It was observed that after 40th use in 5 days, the retained activities for covalently immobilized and entrapped lipases were found as 39% and 22%, respectively. Storage and thermal stability of enzyme was also increased by as a result of immobilization procedures.     

Evidence for catalytic cooperativity during ATP hydrolysis by beef heart F1-ATPase. Kinetics and binding studies with the photoaffinity label BzATP

The photoaffinity analog of ATP, 3'-O-(4-benzoyl) benzoyl ATP (BzATP), was used to covalently modify the catalytic sites on the beef heart mitochondrial F1-ATPase. In the absence of actinic illumination, BzATP was a slow substrate for the enzyme (Vmax = 0.19 mumol min-1 mg-1; kcat/Km = 2.2 X 10(6) M-1s-1) and behaved as a classical competitive inhibitor versus ATP (Ki = 0.85 microM). Under photolytic conditions, BzATP inactivated F1 with pseudo first-order kinetics, and the photoinactivation reaction showed rate saturation suggesting specific, reversible binding of BzATP to F1 prior to covalent bond formation. ATP protected against F1 photoinactivation (Kprotect = 0.3 microM) and partially covalently modified F1 yielded the same Km for ATP as unmodified enzyme. These results strongly suggested that BzATP was bound to catalytic sites on the enzyme. In the absence of photolysis, BzATP saturated two binding sites on the F1 (KD = 1.6 microM), and under photolytic conditions, 1 mol of BzATP was shown to be covalently liganded to the beta subunit of the enzyme coincident with 100% loss in ATPase activity. Previous studies with the mitochondrial F1-ATPase have suggested a mechanism involving catalytic cooperativity during ATP hydrolysis. Our demonstration of a molar stoichiometry of 1 for photoinactivation is in accord with this mechanism. It is suggested that either F1 is unable to hydrolyze covalently bound BzATP, or that subsequent to hydrolysis, the BzADP product can not be released from the catalytic site. It is therefore inferred that F1 hydrolytic activity requires cooperativity between multiple, viable catalytic sites and that covalent modification of a single catalytic site is sufficient for complete enzyme inactivation.     

Electrochemical studies on horseradish peroxidase covalently coupled with redox dyes

The present study aims at investigating the use of redox dyes as non-diffusional electron mediators in hydrogen peroxide biosensors using horseradish peroxidase (HRP). We observe that the two redox dyes Safranine O and Neutral Red covalently bound to HRP, efficiently mediate electron transfer from the active site of the enzyme to the electrode surface. Dyes bound to the enzyme using a spacer arm diaminohexane further enhance the electron transfer. The enzyme electrodes show a linear response to the concentration of H2O2 up to 500 microM concentration and with a detection limit of around 50 microM. The dyes can be used as coupled mediators to develop a successful electro-optical biosensor.     

Stability of free and immobilised peroxidase in aqueous–organic solvents mixtures

The activity and stability of horseradish (Amoracia rusticana) peroxidase (HRP) free in solution and immobilised onto silica microparticles was studied in the presence of organic co-solvents.

The effect of several hydrophilic organic solvents, namely dimethyl sulfoxide, dimethylformamide, dioxan, acetonitrile and tetrahydrofuran, in the activity and stability of free HRP was studied. From the solvents tested, DMSO led to the highest activities and stabilities. After 2 h of incubation at 35°C, the remaining activity of the enzyme in the presence of 30% of each solvent was less than 30%, with exception of DMSO for which the enzyme remained fully active.

In order to increase stability, HRP was covalently immobilised onto silica microparticles. The half-life of the enzyme in buffer at 50°C increased from 2 to 52 h when the enzyme was immobilised. The stability of both free and immobilised HRP was also studied at 50°C in aqueous mixtures of 3.5, 20, 35 and 50% (v/v) DMSO. Free HRP stability was not affected by the presence of 3.5 and 20% DMSO, but higher contents lead to a more pronounced deactivation. Immobilised HRP stability increased with DMSO content up to 20%, decreasing for higher contents. The enzyme half-life increased more than 300% when changing from buffer to 20% DMSO.

The deactivation of free HRP was modelled using the simple exponential decay, and the deactivation of immobilised HRP was described by a two-step inactivation model.     

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.     

The potential use of hydrazine as an alternative to peroxidase in a biosensor: comparison between hydrazine and HRP-based glucose sensors

The potential use of hydrazine sulfate was examined for the catalytic reduction of enzymatically generated H2O2 in a biosensor system. The performance of the hydrazine-based sensor was compared with an HRP-based glucose sensor as a model of a biosensor. Hydrazine and HRP were covalently immobilized onto a conducting polymer layer with glucose oxidase. The direct electron transfer reactions of the immobilized hydrazine and HRP onto the poly-5,2':5,2'-terthiophene-3'-carboxylic acid (poly-TTCA) layer were investigated by using cyclic voltammetric method and the electron transfer rate constants were determined. The glucose oxidase- and hydrazine-immobilized sensor efficiently reduced the enzymatically generated H2O2 at -0.15 V versus Ag/AgCl. The surface of this GOx/hydrazine/poly-TTCA-based glucose sensor was characterized by QCM, SEM, and ESCA. Glucose-sensing properties were studied using cyclic voltammetric and chronoamperometric techniques. Various experimental parameters were optimized according to the amount of hydrazine, pH, the temperature, and the applied potential. A linear calibration plot was obtained in the concentration range between 0.1 and 15.0 mM, and the detection limit was determined to be 40.0+/-7.0 microM. Interferences from other biological compounds were studied. The long-term stability of the GOx/hydrazine sensor was better than that of the one based on a GOx/HRP biosensor. The proposed glucose sensor was successfully applied to human whole blood and urine samples for the detection of glucose.     

Structural stabilization and functional improvement of horseradish peroxidase upon modification of accessible lysines: experiments and simulation

Horseradish peroxidase (HRP) is an important heme enzyme with enormous medical diagnostic, biosensing, and biotechnological applications. Thus, any improvement in the applicability and stability of the enzyme is potentially interesting. We previously reported that covalent attachment of an electron relay (anthraquinone 2-carboxylic acid) to the surface-exposed Lys residues successfully improves electron transfer properties of HRP. Here we investigated structural and functional consequences of this modification, which alters three accessible charged lysines (Lys-174, Lys-232, and Lys-241) to the hydrophobic anthraquinolysine residues. Thermal denaturation and thermoinactivation studies demonstrated that this kind of modification enhances the conformational and operational stability of HRP. The melting temperature increased 3 degrees C and the catalytic efficiency enhanced by 80%. Fluorescence and circular dichroism investigations suggest that the modified HRP benefits from enhanced aromatic packing and more buried hydrophobic patches as compared to the native one. Molecular dynamics simulations showed that modification improves the accessibility of His-42 and the heme prosthetic group to the peroxide and aromatic substrates, respectively. Additionally, the hydrophobic patch, which functions as a binding site or trap for reducing aromatic substrates, is more extended in the modified enzyme. In summary, this modification produces a new derivative of HRP with enhanced electron transfer properties, catalytic efficiency, and stability for biotechnological applications.     

Poly(2-hydroxyethyl methacrylate) for enzyme immobilization: impact on activity and stability of horseradish peroxidase

On the basis of their versatile structure and chemistry as well as tunable mechanical properties, polymer brushes are well-suited as supports for enzyme immobilization. However, a robust surface design is hindered by an inadequate understanding of the impact on activity from the coupling motif and enzyme distribution within the brush. Herein, horseradish peroxidase C (HRP C, 44 kDa), chosen as a model enzyme, was immobilized covalently through its lysine residues on a N-hydroxysuccinimidyl carbonate-activated poly(2-hydroxyethyl methacrylate) (PHEMA) brush grafted chemically onto a flat impenetrable surface. Up to a monolayer coverage of HRP C is achieved, where most of the HRP C resides at or near the brush-air interface. Molecular modeling shows that lysines 232 and 241 are the most probable binding sites, leading to an orientation of the immobilized HRP C that does not block the active pocket of the enzyme. Michaelis-Menten kinetics of the immobilized HRP C indicated little change in the K(m) (Michaelis constant) but a large decrease in the V(max) (maximum substrate conversion rate) and a correspondingly large decrease in the k(cat) (overall catalytic rate). This indicates a loss in the percentage of active enzymes. Given the relatively ideal geometry of the HRPC-PHEMA brush, the loss of activity is most likely due to structural changes in the enzyme arising from either secondary constraints imposed by the connectivity of the N-hydroxysuccinimidyl carbonate linking moiety or nonspecific interactions between HRP C and DSC-PHEMA. Therefore, a general enzyme-brush coupling motif must optimize reactive group density to balance binding with neutrality of surroundings.     

Photoimmobilization of organophosphorus hydrolase within a PEG-based hydrogel.

Organophosphorous hydrolase (OPH) was physically and covalently immobilized within photosensitive polyethylene glycol (PEG)-based hydrogels. The hydroxyl ends of branched polyethylene glycol (b-PEG, four arms, MW = 20,000) were modified with cinnamylidene acetate groups to give water-soluble, photosensitive PEG macromers (b-PEG-CA). The b-PEG-CA macromers underwent photocrosslinking reaction and formed gels upon UV irradiation (>300 nm) in the presence of erythrosin B. Native OPH was pegylated with cinnamylidene-terminated PEG chains (MW = 3400) to be covalently linked with the b-PEG-CA macromers during photogelation. The effect of pegylation on the stability of the enzyme was determined. Furthermore, the effect of enzyme concentration, wavelength of irradiation, and photosensitizer on the stability of the entrapped enzyme was also investigated. The pegylated OPH was more stable than the native enzyme, and the OPH-containing gels exhibited superior stability than the soluble enzyme preparations.     

Additional factors influencing sensitivity in the tetramethyl benzidine method for horseradish peroxidase neurohistochemistry

In experiments that use horseradish peroxidase (HRP) and tetramethyl benzidine (TMB) for tracing neural connections, the activity of tissue-bound enzyme as well as the stability of the resultant reaction product are influenced by the duration of storage, the composition of the storage medium, the type of counterstaining and even the details of histological dehydration. Furthermore, the conditions for preserving HRP activity are very different from those necessary for preserving the stability of the tetramethyl benzidine (TMB) reaction product. Thus, tissue-bound HRP activity is stable at a neutral pH, while a much lower pH, around 3.3, is required for preserving the stability of the TMB reaction product. Recent evidence indicates that the stabilization bath in sodium nitroferricyanide that was previously recommended is not necessary. However, gradual dehydration of mounted sections is essential for long-term stability. Excessive counterstaining and excessive dehydration interfere with the detection of reaction product. These considerations are pertinent to experiments using free HRP as well as to those where the enzyme has been conjugated to wheat germ agglutinin.     

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.     

Operational stability of copolymerized enzymes at elevated temperatures

The copolymerization method of immobilization was used to obtain preparations of enzymes covalently incorporated in polyacrylamide gel. They possess properties making them suitable for practical use. First, the preparations are hundreds of times more stable against irreversible thermoinactivation than native enzymes. Second, on immobilization, the reversible conformational changes which also lower enzyme activity at elevated temperatures are completely suppressed. As a result, the temperatures of maximum activity for trypsin and alpha-chymotrypsin covalently entrapped in polyacrylamide gel are 75 and 70 degrees C, respectively-25 and 30 degrees C higher than the corresponding values for the native enzymes. Therefore, the copolymerized enzyme preparations have a high operational stability at elevated temperatures.     

Disposable amperometric immunosensor system for rabbit IgG using a conducting polymer modified screen-printed electrode

A disposable and mediatorless immunosensor based on a conducting polymer (5,2':5'2"-terthiophene-3'-carboxylic acid) coated screen-printed carbon electrode has been developed using a separation-free homogeneous technique for the detection of rabbit IgG as a model analyte. Horseradish peroxidase (HRP) and streptavidin were covalently bonded with the polymer on the electrode and biotinylated antibody was immobilized on the electrode surface using avidin-biotin coupling. This sensor was based on the competitive assay between free and labeled antigen for the available binding sites of antibody. Glucose oxidase was used as a label and in the presence of glucose, H(2)O(2) formed by the analyte-enzyme conjugate was reduced by the enzyme channeling via HRP bonded on the electrode. The catalytic current was monitored amperometrically at -0.35 V vs. Ag/AgCl and this method showed a linear range of RIgG concentrations from 0.5 to 2 microg/ml with standard deviation +/-0.0145 (n=4). Detection limit was determined to be 0.33 microg/ml.     

Immobilization of cellulase from newly isolated strain Bacillus subtilis TD6 using calcium alginate as a support material

Bacillus subtilis TD6 was isolated from Takifugu rubripes, also known as puffer fish. Cellulase from this strain was partially purified by ammonium sulphate precipitation up to 80% saturation, entrapped in calcium alginate beads, and finally characterized using CMC as the substrate. For optimization, various parameters were observed, including pH maximum, temperature maximum, sodium alginate, and calcium chloride concentration. pH maximum of the enzyme showed no changes before and after immobilization and remained stable at 6.0. The temperature maximum showed a slight increase to 60 °C. Two percent sodium alginate and a 0.15 M calcium chloride solution were the optimum conditions for acquisition of enzyme with greater stability. K (m) and V (max) values for the immobilized enzyme were slightly increased, compared with those of free enzyme, 2.9 mg/ml and 32.1 μmol/min/mL, respectively. As the purpose of immobilization, reusability and storage stability of the enzyme were also observed. Immobilized enzyme retained its activity for a longer period of time and can be reused up to four times. The storage stability of entrapped cellulase at 4 °C was found to be up to 12 days, while at 30 °C, the enzyme lost its activity within 3 days.     

Binding of divalent metal ions to calcium-free peroxidase: thermodynamic and kinetic studies

Thermodynamics of binding of divalent metal ions including Ca(2+) , Mg(2+) , Ba(2+) , and Cd(2+) to Ca-free horseradish peroxidase (HRP) enzyme was investigated using UV/VIS spectrophotometry and molecular-mechanic (MM) calculations. According to the obtained binding and thermodynamic parameters, trend of the relative binding affinities of these divalent metal cations was found to be: Ca(2+) >Cd(2+) >Mg(2+) >Ba(2+) . Binding analysis based on Scatchard and Hill models showed positive cooperativity effect between the two distal and proximal binding sites. Furthermore, kinetics of binding and reconstitution process was examined (using relaxation-time method) for binding of Ca(2+) (as the typical metal ion) to Ca-free HRP, which was found a second-order type having a two-step mechanism involving fast formation of Ca-free HRP/1?Ca(2+) as the kinetic intermediate in step 1. Finally, by means of MM calculations, the comparative stability energies were evaluated for binding of M(2+) metal cations to Ca-free HRP. Based on MM calculations, preferential binding of Ca(2+) ion was occurred on distal and proximal binding sites of Ca-free HRP associated with higher stability energies (E(total) ). Indeed, among the divalent metal ions, Ca(2+) with the highest binding affinity (maximum value of K(bin) and minimum value of ΔG$\rm{{_{bin}^{0}}}$), maximum value of exothermic binding enthalpy, and stability energies stabilizes the HRP structure along with an optimized catalytic activity.