Immobilization of horseradish peroxidase on modified chitosan beads

Broad-spectrum pH functional chitosan-phosphatase beads for the generation of plant-available phosphorus: utilizing the insoluble P pool

Utilization of organic phosphates and insoluble phosphates for the gradual generation of plant-available phosphorus (P) is the only sustainable solution for P fertilization. Enzymatic conversions are one of the best sustainable routes for releasing P to soil. Phosphatase enzyme aids in solubilizing organic and insoluble phosphates to plant-available P. We herein report the preparation of highly functional chitosan beads co-immobilized with acid phosphatase and alkaline phosphatase enzymes via a glutaraldehyde linkage. The dual enzyme co-immobilized chitosan beads were characterized using Fourier-transform infrared (FTIR), thermogravimetric (TGA), and scanning electron microscopy-energy dispersive x-ray (SEM-EDX) analyses to confirm the immobilization. The co-immobilized system was found to be active for a broader pH range of ∼4-10 than the individually bound enzymes and mixed soluble enzymes. The bound matrix exhibited pH optima at 6 and 9, respectively, for acid and alkaline phosphatase and a temperature optimum at 50°C. The phosphate-solubilizing abilities of the chitosan-enzyme derivatives were examined using insoluble tri-calcium phosphate (TCP) for wide pH conditions of 5.5, 7, and 8.5 up to 25 days. The liberation of phosphate was highest (27.20 mg/mL) at pH 5.5 after the defined period. The residual soil phosphatase activity was also monitored after 7 days of incubation with CBE for three different soils of pH ∼5.5, 7, and 8.5. The residual phosphatase activity increased for all the soils after applying the CBE. The germination index of the Oryza sativa (rice) plant was studied using different pH buffer media upon the application of the CBE in the presence of tri-calcium phosphate as a phosphate source. Overall, the dual-enzyme co-immobilized chitosan beads were highly effective over a wide pH range for generating plant-available phosphates from insoluble phosphates. The chitosan-enzyme derivative holds the potential to be used for sustainable phosphorus fertilization with different insoluble and organic phosphorus sources.

Immobilization of enzymes on functionalized cellulose nanofibrils for bioremediation of antibiotics: Degradation mechanism, kinetics, and thermodynamic study

The deteriorating environmental conditions due to increasing emerging recalcitrant pollutants raised a severe concern for its remediation. In this study, we have reported antibiotic degradation using free and immobilized HRP. The functionalized cellulose support was utilized for efficient immobilization of HRP. Approximately 13.32 ± 0.52 mg/g enzyme loading was achieved with >99% immobilization efficiency. The higher percentage of immobilization is attributed to the higher surface area and carboxylic groups on the support. The kinetic parameter of immobilized enzymes was Km = 2.99 mM/L for CNF-CA@HRP, which is 3.5-fold more than the Michaelis constant (Km = 0.84794 mM/L) for free HRP. The Vmax of CNF-CA@HRP bioconjugate was 2.36072 mM/min and 0.558254 mM/min for free HRP. The highest degradation of 50, 54.3, and 97% were achieved with enzymatic, sonolysis, and sono-enzymatic with CNF-CA@HRP bioconjugate, respectively. The reaction kinetics analysis revealed that applying ultrasound with an enzymatic process could enhance the reaction rate by 2.7-8.4 times compared to the conventional enzymatic process. Also, ultrasound changes the reaction from diffusion mode to the kinetic regime with a more oriented and fruitful collision between the molecules. The thermodynamic analysis suggested that the system was endothermic and spontaneous. While LC-MS analysis and OTC's degradation mechanism suggest, it mainly involves hydroxylation, secondary alcohol oxidation, dehydration, and decarbonylation. Additionally, the toxicity test confirmed that the sono-enzymatic process helps toward achieving complete mineralization. Further, the reusability of bioconjugate shows that immobilized enzymes are more efficient than the free enzyme.

Enzyme-triggered approach to reduce water bodies' contamination using peroxidase-immobilized ZnO/SnO2/alginate nanocomposite

Enzyme immobilization on solid support offers advantages over free enzymes by overcoming characteristic limitations. To synthesize new stable and hyperactive nano-biocatalysts (co-precipitation method), ginger peroxidase (GP) was surface immobilized (adsorption) on ZnO/SnO2 and ZnO/SnO2/SA nanocomposite with immobilization efficacy of 94 % and 99 %, respectively. Thereafter, catalytic and biochemical characteristics of free and immobilized GP were investigated by deploying various techniques, i.e., FTIR, PXRD, SEM, and PL. Diffraction peaks emerged at 2θ values of 26°, 33°, 37°, 51°, 31°, 34°, 36°, 56°, indicating the formation of SnO2 and ZnO. The OH stretching of the H2O molecules was attributed to broad peaks between 3200 and 3500 cm-1, whereas ZnO/SnO2 spikes occurred in the 1626-1637 cm-1 range. SnO stretching mode and ZnO terminal vibrational patterns have been verified at corresponding wavelengths of 625 cm-1 and 560 cm-1. Enzyme entrapment onto substrate was verified via interactions between GP and ZnO/SnO2/SA as corroborated by signals beneath 1100 cm-1. GP-immobilized fractions were optimally active at pH 5, 50 °C, and retained maximum activity after storage of 4 weeks at -4 °C. Kinetic parameters were determined by using a Lineweaver-Burk plot and Vmax for free GP, ZnO/SnO2/GP and ZnO/SnO2/SA/GP with guaiacol as a substrate, were found to be 322.58, 49.01 and 11.45 (μM/min) respectively. A decrease in values of Vmax and KM indicates strong adsorption of peroxidase on support and maximum affinity between nano support and enzyme, respectively. For environmental remediation, free ginger peroxidase (GP), ZnO/SnO2/GP and ZnO/SnO2/SA/GP fractions effectively eradicated highly intricate dye. Multiple scavengers had a significant impact on the depletion of the dye. In conclusion, ZnO/SnO2 and ZnO/SnO2/SA nanostructures comprise an ecologically acceptable and intriguing carrier for enzyme immobilization.

Nanotechnology-assisted treatment of pharmaceuticals contaminated water

The presence of pharmaceutical compounds in wastewater due to an increase in industrialization and urbanization is a serious health concern. The demand for diverse types of pharmaceutical compounds is expected to grow as there is continuous improvement in the global human health standards. Discharge of domestic pharmaceutical personal care products and hospital waste has aggravated the burden on wastewater management. Further, the pharmaceutical water is toxic not only to the aquatic organism but also to terrestrial animals coming in contact directly or indirectly. The pharmaceutical wastes can be removed by adsorption and/or degradation approach. Nanoparticles (NPs), such as 2D layers materials, metal-organic frameworks (MOFs), and carbonaceous nanomaterials are proven to be more efficient for adsorption and/or degradation of pharmaceutical waste. In addition, inclusion of NPs to form various composites leads to improvement in the waste treatment efficacy to a greater extent. Overall, carbonaceous nanocomposites have advantage in the form of being produced from renewable resources and the nanocomposite material is biodegradable either completely or to a great extent. A comprehensive literature survey on the recent advancement of pharmaceutical wastewater is the focus of the present article.

Application of Immobilized Enzymes in Juice Clarification

Immobilized enzymes are currently being rapidly developed and are widely used in juice clarification. Immobilized enzymes have many advantages, and they show great advantages in juice clarification. The commonly used methods for immobilizing enzymes include adsorption, entrapment, covalent bonding, and cross-linking. Different immobilization methods are adopted for different enzymes to accommodate their different characteristics. This article systematically reviews the methods of enzyme immobilization and the use of immobilized supports in juice clarification. In addition, the mechanisms and effects of clarification with immobilized pectinase, immobilized laccase, and immobilized xylanase in fruit juice are elaborated upon. Furthermore, suggestions and prospects are provided for future studies in this area.

Efficiency Assessment between Entrapment and Covalent Bond Immobilization of Mutant β-Xylosidase onto Chitosan Support

The Y509E mutant of β-xylosidase from Geobacillus stearothermophilus (XynB2Y509E) (which also bears xylanase activity) has been immobilized in chitosan spheres through either entrapment or covalent bond formation methods. The maximum immobilization yield by entrapment was achieved by chitosan beads developed using a 2% chitosan solution after 1 h of maturation time in CFG buffer with ethanol. On the other hand, the highest value in covalent bond immobilization was observed when employing chitosan beads that were prepared from a 2% chitosan solution after 4 h of activation in 1% glutaraldehyde solution at pH 8. The activity expressed after immobilization by covalent bonding was 23% higher compared to the activity expressed following entrapment immobilization, with values of 122.3 and 99.4 IU.g-1, respectively. Kinetic data revealed that catalytic turnover values were decreased as compared to a free counterpart. Both biocatalysts showed increased thermal and pH stability, along with an improved storage capacity, as they retained 88% and 40% of their activity after being stored at 4 °C for two months. Moreover, XynB2Y509E immobilized by covalent binding also exhibited outstanding reusability, retaining 92% of activity after 10 cycles of reuse. In conclusion, our results suggest that the covalent bond method appears to be the best choice for XynB2Y509E immobilization.

Acrylic fabric and nanomaterials to enhance α-amylase-based biocatalytic immobilized systems for industrial food applications

An innovative approach for immobilizing α-amylase was used in this investigation. The acrylic fabric was first treated with hexamethylene diamine (HMDA) and then coated with copper ions that were later reduced to copper nanoparticles (CuNPs). The corresponding materials obtained, Cu(II)@HMDA-TA and CuNPs@HMDA-TA, were employed as carriers for α-amylase, respectively. The structural and morphological characteristics of the produced support matrices before and after immobilization were assessed using various techniques, including FTIR, SEM, EDX, TG/DTG, DSC, and zeta potential. The immobilized α-amylase exhibited the highest level of activity at pH 7.0, with immobilization yields observed for CuNPs@HMDA-TA (81.7 %) (60 unit/g support) followed by Cu(II)@HMDA-TA (71.7 %) (49 unit/g support) and 75 % and 61 % of activity yields, and 91.7 % and 85 % of immobilization efficiency, respectively. Meanwhile, biochemical characterizations of the activity of the soluble and immobilized enzymes were carried out and compared. Optimal temperature, pH, kinetics, storage stability, and reusability parameters were optimized for immobilized enzyme activity. The optimal pH and temperature were recorded as 6.0 and 50 °C for soluble α-amylase while the two forms of immobilized α-amylase exhibit a broad pH of 6.0-7.0 and optimal temperature at 60 °C. After recycling 15 times, the immobilized α-amylase on CuNPs@HMDA-TA and Cu(II)@HMDA-TA preserved 63 % and 52 % of their activities, respectively. The two forms of immobilized α-amylase displayed high stability when stored for 6 weeks and preserved 85 % and 76 % of their activities, respectively. Km values were calculated as 1.22, 1.39, and 1.84 mg/mL for soluble, immobilized enzymes on CuNPs@HMDA-TA, and Cu(II)@HMDA-TA, and Vmax values were calculated as 36.25, 29.68, and 21.57 μmol/mL/min, respectively. The total phenolic contents of maize kernels improved 1.4 ± 0.01 fold after treatment by two immobilized α-amylases.

Developing a robust method integrating with selective membrane-based preconcentration and signal amplification for field virus detection

Infectious diseases caused by viruses have attracted global concern owing to their rapid spread and catastrophic consequences. Therefore, developing fast and reliable on-site virus detection methods is essential for the prevention and treatment of virus-related diseases. In this study, immunoassays on a membrane, combining virus preconcentration with nanoparticle-based signal amplification, were used to realize the rapid and accurate visual detection of viruses. The biotin-streptavidin scaffolds for target virus preconcentration were established on a membrane, and subsequently a Zika aptamer (Apt) immobilized on the membrane recognized and captured the nonstructural protein 1 of Zika virus (ZIKV-NS1). The probe for detection was synthesized by conjugating the Zika Apt with a high level of horseradish peroxidase on gold nanoparticles. The ZIKV-loaded membrane was incubated with the probes, and the viral signal was amplified as the signal of horseradish peroxidase. In the presence of 3,3,5',5'-tetramethyl benzidine and hydrogen peroxide, the green color of the probe-coated membrane indicated the level of ZIKV-NS1. Our developed method could reach a detection limit of 5 ng mL^-1, and the whole procedure could be completed within 1 h. Analyses of rabbit serum and environmental water samples demonstrated that an immunoassay-based approach on the membrane could accurately determine the level of ZIKV-NS1 against the complicated matrix. Our results suggest that this virus detection method has a high potential for application in clinical and environmental settings.

Peroxidase-Mimicking Activity of Biogenic Gold Nanoparticles Produced from Prunus nepalensis Fruit Extract: Characterizations and Application for the Detection of Mycobacterium bovis

In the present study, a facile, eco-friendly, and controlled synthesis of gold nanoparticles (Au NPs) using Prunus nepalensis fruit extract is reported. The biogenically synthesized Au NPs possess ultra-active intrinsic peroxidase-like activity for the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2. Chemical analysis of the fruit extract demonstrated the presence of various bioactive molecules such as amino acids (l-alanine and aspartic acids), organic acids (benzoic acid and citric acid), sugars (arabinose and glucose), phenolic acid, and bioflavonoids (niacin and myo-inositol), which likely attributed to the formation of stable biogenic Au NPs with excellent peroxidase-mimicking activity. In comparison with the natural horseradish peroxidase (HRP) enzyme, the biogenic Au NPs displayed a 9.64 times higher activity with regard to the reaction velocity at 6% (v/v) H2O2, presenting a higher affinity toward the TMB substrate. The Michaelis-Menten constant (KM) values for the biogenic Au NPs and HRP were found to be 6.9 × 10-2 and 7.9 × 10-2 mM, respectively, at the same concentration of 100 pM. To investigate its applicability for biosensing, a monoclonal antibody specific for Mycobacterium bovis (QUBMA-Bov) was directly conjugated to the surface of the biogenic Au NPs. The obtained results indicate that the biogenic Au NPs-QUBMA-Bov conjugates are capable of detecting M. bovis based on a colorimetric immunosensing method within a lower range of 100 to 102 cfu mL-1 with limits of detection of ∼53 and ∼71 cfu mL-1 in an artificial buffer solution and in a soft cheese spiked sample, respectively. This strategy demonstrates decent specificity in comparison with those of other bacterial and mycobacterial species. Considering these findings together, this study indicates the potential for the development of a cost-effective biosensing platform with high sensitivity and specificity for the detection of M. bovis using antibody-conjugated Au nanozymes.

Amorphous metal-organic frameworks on PtCu hydrogels: Enzyme immobilization platform with boosted activity and stability for sensitive biosensing

Cell-free enzymatic catalysis (CFEC) is emerging biotechnology that simulates biological transformations without living cells. However, the high cost of separation and preparation of the enzyme has hindered the practical application of the CFEC. Enzyme immobilization technologies using solid supports to stabilize enzymes have been regarded as an efficient strategy to address this issue. Nevertheless, the activity and stability of the immobilized enzymes are still crucial challenges for working in vitro. Herein, an enzyme immobilization platform is developed by using PtCu hydrogels coated with amorphous metallic-organic frameworks (MOFs) as multifunctional carriers to encapsulate horseradish peroxidase (HRP). Specifically, PtCu hydrogels acting as a "reservoir of metal ions" can interact with the immobilized enzyme and facilitate electron transfer, leading to the boosted enzyme catalytic performances. Furthermore, amorphous MOFs on the surface of PtCu hydrogels serve as an "armor" to protect the internal enzymes from various perturbation environments. The resultant enzyme immobilization platform (PtCu@HRP@ZIF-8) not only shows an approximately 2.4-fold enhanced activity compared with free enzyme but also exhibits improved stability against harsh conditions. The PtCu@HRP@ZIF-8-based biosensor is constructed for sensitive sensing of organophosphorus pesticides (OPs). The proposed biosensor exhibits a favorable linear relationship with the concentration of paraoxon-ethyl from 6 to 800 ng/mL, with a low detection limit of 1.8 ng/mL. This work reveals the promising potential of our proposed enzyme immobilization platform in practical applications.

Immobilization of horseradish peroxidase on lysine-functionalized gum Arabic-coated Fe3O4 nanoparticles for cholesterol determination

BACKGROUND

Horseradish Peroxidase (HRP) is ranked as one of the most important industrial enzymes that is extensively used in industry. Cholesterol is routinely detected indirectly by cholesterol oxidase in the presence of O₂, liberating H₂O₂ as a by-product. The H₂O₂ content is determined through the HRP activity in the presence of a redox dye, producing a red colored quinoneimine which can be measured quantitatively. Herein, we have designed a magnetic nanoparticle for reusing and easily separating HRP as the most expensive compartment for the low-cost cholesterol assay.

METHODS

The gum Arabic coated magnetic nanoparticles were functionalized with L-lysine linker for maintaining protein flexibility on nanoparticle. Enzyme-loaded nanoparticles were characterized by TEM, FTIR, DLS, VSM and XRD analysis.

RESULTS

The immobilization efficiency was ∼65% and the immobilized HRP retained 60% of its activity after 8 times reuse. The optimum pH and thermal stability shifted from 7.0 to 8.0 and 60 to 70 °C after immobilization, respectively. Storage stability of HRP was improved by 10%, at 4 °C for 60 days. Immobilized HRP showed more catalytic activity in presence of Fe²⁺, Ca²⁺ and Na⁺. The designed system has cholesterol detection linearity range from 0.2 to 5.0 mM and detection limit of 0.08 mM and acceptable correlation coefficient of 0.9973 and 0.9982 on sample serum using both chromogens.

CONCLUSION

The HRP-loaded magnetic nanoparticles are capable of being used as a cost-effective system for cholesterol determination in laboratory due to its reusability and stability benefits.

Development of polymer-based multifunctional composite particles of protease and peroxidase activities

A hybrid material (SL-PPN-HEP-HRP) of dual enzyme function was prepared by co-immobilization of papain (PPN) and horseradish peroxidase (HRP) on sulphate latex (SL) microspheres using heparin (HEP) polyelectrolyte as a building block in the sequential adsorption method. The doses of PPN, HEP and HRP were optimized in each step of the preparation process to achieve high functional and colloidal stability. The enzymes and the polyelectrolyte strongly adsorbed on the oppositely charged surfaces via electrostatic forces, and enzyme leakage was not observed from the hybrid material, as confirmed by colorimetric protein tests and microscopy measurements. It was found that the polyelectrolyte acted as a separator between PPN and HRP to prevent hydrolytic attack on the latter enzyme, which otherwise prevents the joint use of these important biocatalysts. Excellent colloidal stability was obtained for the SL-PPN-HEP-HRP composite and the embedded PPN and HRP showed remarkable protease and peroxidase activities, respectively, at least until five days after preparation. The present results offer a promising approach to develop biocatalytic systems of dual function, which are often required in manufacturing processes in the food industry, where the colloidal stability of such multifunctional materials is a key parameter to achieve remarkable efficiency.

Enzyme prodrug therapy: cytotoxic potential of paracetamol turnover with recombinant horseradish peroxidase

Targeted cancer treatment is a promising, less invasive alternative to chemotherapy as it is precisely directed against tumor cells whilst leaving healthy tissue unaffected. The plant-derived enzyme horseradish peroxidase (HRP) can be used for enzyme prodrug cancer therapy with indole-3-acetic acid or the analgesic paracetamol (acetaminophen). Oxidation of paracetamol by HRP in the presence of hydrogen peroxide leads to N-acetyl-p-benzoquinone imine and polymer formation via a radical reaction mechanism. N-acetyl-p-benzoquinone imine binds to DNA and proteins, resulting in severe cytotoxicity. However, plant HRP is not suitable for this application since the foreign glycosylation pattern is recognized by the human immune system, causing rapid clearance from the body. Furthermore, plant-derived HRP is a mixture of isoenzymes with a heterogeneous composition. Here, we investigated the reaction of paracetamol with defined recombinant HRP variants produced in E. coli, as well as plant HRP, and found that they are equally effective in paracetamol oxidation at a concentration ≥ 400 µM. At low paracetamol concentrations, however, recombinant HRP seems to be more efficient in paracetamol oxidation. Yet upon treatment of HCT-116 colon carcinoma and FaDu squamous carcinoma cells with HRP-paracetamol no cytotoxic effect was observed, neither in the presence nor absence of hydrogen peroxide.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s00706-021-02848-x.

Peroxidase driven micromotors for dynamic bioremediation

Phenolics are size products present in tons concentrations in industrial wastewater that can cause adverse health effects when released in the environment. As such, there is a growing interest in the development of efficient strategies for the removal of phenolic compounds from polluted water. Herein we describe the use of poly(3,4-ethylenedioxythiophene) (PEDOT)-Au/peroxidase micromotors as dynamic biocatalytic platforms for the removal of model phenolics (phenol, bisphenol A, guaiacol, pyrogallol and catechol). Micromotors are synthetized by using a simplified template electrodeposition protocol followed by covalent enzyme immobilization in the inner Au layer. Kinetic parameters revealed that enzyme immobilization in the inner micromotor layer increased over 2-fold the enzymatic activity, along with increasing operational pH and thermal stabilities. The micromotors can propel at speed of up to 60 µm/s, generating an enhanced fluid mixing that results in removal efficiencies of up to 60% as compared with the 27% removal when using free peroxidase under the same conditions. In addition, excellent activities of almost 100% were obtained within ten cycles of removal using the micromotors. This newly developed bioremediation strategy holds considerable promise in for its application in large scale water treatment systems and many relevant environmental processes.

Hyaluronic acid-coated chitosan nanoparticles as carrier for the enzyme/prodrug complex based on horseradish peroxidase/indole-3-acetic acid: Characterization and potential therapeutic for bladder cancer cells

Hybrid nanoparticles composed of different biopolymers for delivery of enzyme/prodrug systems are of interest for cancer therapy. Hyaluronic acid-coated chitosan nanoparticles (CS/HA NP) were prepared to encapsulate individually an enzyme/pro-drug complex based on horseradish peroxidase (HRP) and indole-3-acetic acid (IAA). CS/HA NP showed size around 158 nm and increase to 170 and 200 nm after IAA and HRP encapsulation, respectively. Nanoparticles showed positive zeta potential values (between +20.36 mV and +24.40 mV) and higher encapsulation efficiencies for both nanoparticles (up to 90 %) were obtained. Electron microscopy indicated the formation of spherical particles with smooth surface characteristic. Physicochemical and thermal characterizations suggest the encapsulation of HRP and IAA. Kinetic parameters for encapsulated HRP were similar to those of the free enzyme. IAA-CS/HA NP showed a bimodal release profile of IAA with a high initial release (72 %) followed by a slow-release pattern. The combination of HRP-CS/HA NP and IAA- CS/HA NP reduced by 88 % the cell viability of human bladder carcinoma cell line (T24) in the concentrations 0.5 mM of pro-drug and 1.2 μg/mL of the enzyme after 24 h.

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.

Transformation of sulfadiazine in humic acid and polystyrene microplastics solution by horseradish peroxidase coupled with 1-hydroxybenzotriazole

Enzyme catalyzed coupling with redox mediators are considered as great interesting and viable technologies to transform antibiotics. This work demonstrated the horseradish peroxidase (HRP) was effective in transforming sulfadiazine (SDZ) transformation coupled with 1-hydroxybenzotriazole (HBT) at varying conditions. The removal of SDZ was independent of Na⁺ and its ionic strength, but Ca²⁺ could enhance transformation efficiency by increasing the enzyme activity of HRP. The presence of humic acid (HA) and polystyrene (PS) microplastics showed inhibition on the transformation of SDZ, and the transformation rate constants (k) decreased with the concentration of HA and PS particles increased. These primarily attributed to covalent coupling and electrostatic interaction between SDZ and HA, SDZ and PS, respectively, which reduced the concentration of free SDZ in the reaction solution. The presence of cation recovered the inhibition of SDZ transformation by HA and PS particles, which ascribed to compete between cation and SDZ. The divalent cations (Ca²⁺) showed more substantial competitiveness than mono (Na⁺) due to more carried charge. Eight possible transformation products were identified, and potential SDZ transformation pathways were proposed, which include δ-cleavage, γ-cleavage, carbonylation, hydroxylation, SO₂ extrusion and SO₃ extrusion. In addition, HA and PS particles couldn't affect the transformation pathways of SDZ. These findings provide novel understandings of the transformation and the fate of antibiotics in the natural environment by HRP coupled with redox mediators.

Immobilization of horseradish peroxidase on cationic microporous starch: Physico-bio-chemical characterization and removal of phenolic compounds

In the present study, two different modified starches; microporous starch (MPS) and cationic microporous starch (CMPS) were synthesized. The granules of MPS that distributed regularly were destroyed after the etherification reaction. The data depicted that the immobilization of horseradish peroxidase (HRP) on CMPS revealed highest immobilization efficiency (86%) at 100 mg of CMPS at pH = 6.0 and 100 units of enzyme. After 10 reuses of the CMPS-HRP, it retained 66% of initial activity. The soluble HRP showed broad pH optimum of 6.0-7.0, which changed to sharp pH = 6.0 for CMPS-HRP. Soluble-HRP and CMPS-HRP showed temperature optima at 30 °C and 40 °C, respectively. The CMPS-HRP showed high thermal stability up to 50 °C compared to the soluble HRP (40 °C). The Km values of soluble HRP and CMPS-HRP were 6.6 and 10.8 mM for H₂O₂ and 34 and 41.6 mM for guaiacol, respectively. CMPS-HRP showed higher affinity toward various substrates than the soluble-HRP. CMPS-HRP showed more resistance against heavy metals, urea, isopropanol, Triton X-100 and trypsin than soluble enzyme. The CMPS-HRP showed higher ability to remove phenol and p-chlorophenol compared to soluble-HRP.

Engineering bioscaffolds for enzyme assembly

With the demand for green, safe, and continuous biocatalysis, bioscaffolds, compared with synthetic scaffolds, have become a desirable candidate for constructing enzyme assemblages because of their biocompatibility and regenerability. Biocompatibility makes bioscaffolds more suitable for safe and green production, especially in food processing, production of bioactive agents, and diagnosis. The regenerability can enable the engineered biocatalysts regenerate through simple self-proliferation without complex re-modification, which is attractive for continuous biocatalytic processes. In view of the unique biocompatibility and regenerability of bioscaffolds, they can be classified into non-living (polysaccharide, nucleic acid, and protein) and living (virus, bacteria, fungi, spore, and biofilm) bioscaffolds, which can fully satisfy these two unique properties, respectively. Enzymes assembled onto non-living bioscaffolds are based on single or complex components, while enzymes assembled onto living bioscaffolds are based on living bodies. In terms of their unique biocompatibility and regenerability, this review mainly covers the current advances in the research and application of non-living and living bioscaffolds with focus on engineering strategies for enzyme assembly. Finally, the future development of bioscaffolds for enzyme assembly is also discussed. Hopefully, this review will attract the interest of researchers in various fields and empower the development of biocatalysis, biomedicine, environmental remediation, therapy, and diagnosis.

Biopolymers and nanostructured materials to develop pectinases-based immobilized nano-biocatalytic systems for biotechnological applications

Pectinases are the emerging enzymes of the biotechnology industry with a 25% share in the worldwide food and beverage enzyme market. These are green and eco-friendly tools of nature and hold a prominent place among the commercially produced enzymes. Pectinases exhibit applications in various industrial bioprocesses, such as clarification of fruit juices and wine, degumming, and retting of plant fibers, extraction of antioxidants and oil, fermentation of tea/coffee, wastewater remediation, modification of pectin-laden agro-industrial waste materials for high-value products biosynthesis, manufacture of cellulose fibres, scouring, bleaching, and size reduction of fabric, cellulosic biomass pretreatment for bioethanol production, etc. Nevertheless, like other enzymes, pectinases also face the challenges of low operational stability, recoverability, and recyclability. To address the above-mentioned problems, enzyme immobilization has become an eminently promising approach to improve their thermal stability and catalytic characteristics. Immobilization facilitates easy recovery and recycling of the biocatalysts multiple times, leading to enhanced performance and commercial feasibility.In this review, we illustrate recent developments on the immobilization of pectinolytic enzymes using polymers and nanostructured materials-based carrier supports to constitute novel biocatalytic systems for industrial exploitability. The first section reviewed the immobilization of pectinases on polymers-based supports (ca-alginate, chitosan, agar-agar, hybrid polymers) as a host matrix to construct robust pectinases-based biocatalytic systems. The second half covers nanostructured supports (nano-silica, magnetic nanostructures, hybrid nanoflowers, dual-responsive polymeric nanocarriers, montmorillonite clay), and cross-linked enzyme aggregates for enzyme immobilization. The biotechnological applications of the resulted immobilized robust pectinases-based biocatalytic systems are also meticulously vetted. Finally, the concluding remarks and future recommendations are also given.

Immobilization of peroxidase on textile carrier materials and their application in the bleaching of colored whey

Textiles represent promising support materials for enzymes. The goal of the present work was to investigate the immobilization of commercial peroxidase on a polyester needle felt and the repeated use in the gentle degradation of norbixin in whey from dairy cheese as a practical application. High enzyme loads were obtained by a 2-step immobilization procedure. First, the number of functional groups on the textile surface was increased by a modification with amino-functional polyvinylamine. Second, the enzyme was immobilized by using 2 types of crosslinking agents. Due to the iron content of peroxidase, inductively coupled plasma-optical emission spectrometry was used for the quantitative determination of the enzyme load on the textile. The enzyme activity was evaluated using common 2,2'-azino-di-(3-ethylbenzthiazoline-6-sulfonic acid) assay for peroxidases. By the variation of enzyme input and crosslinker concentration, a maximal enzyme load of 80 mg/g of textile was achieved, and a maximum specific activity of 57 U/g of textile. For the visualization of the enzyme on the fiber surface, fluorescence microscopy as well as scanning probe microscopy were used. The immobilized peroxidase showed significant activity, even after 50 reuse cycles. In addition, the potential of the new support and enzyme combination in commercial whey bleaching was demonstrated successfully on a 10-L scale.

Pristine and modified chitosan as solid catalysts for catalysis and biodiesel production: A minireview

Chitosan is one of the readily available polymers with relatively high abundance, biodegradable and sustainable materials with divergent functional groups that are employed in broad range of applications. Chitosan is widely used in many fields like adsorption, drug carrier for therapeutic activity, environmental remediation, drug formulation and among others. One of the unique features of chitosan is that it can be transformed to other forms like beads, films, flakes, sponges and fibres depending upon the applications. This review is aimed at showing the potential applications of chitosan and its modified solids in organic transformations. The number of existing articles is organized based on the nature of materials and subsequently with the types of reactions. After a brief description on the structural features of chitosan, properties, characterization methods including various analytical/microscopic techniques and some of the best practices to be followed in catalysis are also discussed. The next section of this review describes the catalytic activity of native chitosan without any modifications while the subsequent sections provide the catalytic activity of chitosan derivatives, chitosan covalently modified with metal complexes/salts through linkers and chitosan as support for metal nanoparticles (NPs). These sections discuss number of organic reactions that include Knoevenagel condensation, oxidation, reduction, heterocycles synthesis, cross-coupling reactions and pollutant degradation among others. A separate section provides the catalytic applications of chitosan and its modified forms for the production of fatty acid methyl esters (FAME) through esterification/transesterification reactions. The final section summarizes our views on the future directions of this field in the coming years.

Transformation mechanisms of tetracycline by horseradish peroxidase with/without redox mediator ABTS for variable water chemistry

The threat of antibiotics in the environment causing antibiotics resistance is a global health concern. Enzymes catalyze pollutant transformations, and how commercially available enzymes like horseradish peroxidase (HRP), with or without a redox mediator, may be used to degrade antibiotics in water treatment is of great interest. This work demonstrates tetracycline transformation by HRP, and how it is significantly enhanced by free radicals created from the mediator 2,2-Azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). Water temperature and pH strongly influence the tetracycline removal rate due to their correlation with the enzyme activity, abundance and stability of ABTS^•+. Four transformation products were identified in the pure HRP system using a liquid chromatography tandem mass spectrometry hybrid quadrupole-orbitrap mass spectrometer system. Addition of 25 μmol L^-1 ABTS not only accelerated the degradation of tetracycline, but also expanded the range of degradation pathways. Potential tetracycline transformation pathways are proposed based on these observations, which include a range of mechanisms such as hydroxylation, demethylation, dehydration, decarbonylation and secondary alcohol oxidation. Despite of decreased efficiency, the HRP/ABTS system was able to degrade tetracycline in a domestic wastewater treatment plant effluent matrix, which demonstrates the potential of the system to be utilized in wastewater treatment.

A Comprehensive Review of the Covalent Immobilization of Biomolecules onto Electrospun Nanofibers

Biomolecule immobilization has attracted the attention of various fields such as fine chemistry and biomedicine for their use in several applications such as wastewater, immunosensors, biofuels, et cetera. The performance of immobilized biomolecules depends on the substrate and the immobilization method utilized. Electrospun nanofibers act as an excellent substrate for immobilization due to their large surface area to volume ratio and interconnectivity. While biomolecules can be immobilized using adsorption and encapsulation, covalent immobilization offers a way to permanently fix the material to the fiber surface resulting in high efficiency, good specificity, and excellent stability. This review aims to highlight the various covalent immobilization techniques being utilized and their benefits and drawbacks. These methods typically fall into two categories: (1) direct immobilization and (2) use of crosslinkers. Direct immobilization techniques are usually simple and utilize the strong electrophilic functional groups on the nanofiber. While crosslinkers are used as an intermediary between the nanofiber substrate and the biomolecule, with some crosslinkers being present in the final product and others simply facilitating the reactions. We aim to provide an explanation of each immobilization technique, biomolecules commonly paired with said technique and the benefit of immobilization over the free biomolecule.

Development of biocatalysts immobilized on coal ash-derived Ni-zeolite for facilitating 4-chlorophenol degradation

A new type of biocatalyst was developed to facilitate the biochemical decomposition of 4-chlorophenol (4-CP) in this study. Oxydoreductases that catalyze the initial steps of 4-CP biodegradation were immobilized on a synthetic inorganic enzyme support. Type-X zeolite, a high-surface area support, was synthesized from coal fly ash, on which nickel ions were plated by impregnation (Ni-zeolite), followed by the effective immobilization (77.5% immobilization yield) of recombinant monooxygenase (CphC-I), dioxygenase (CphA-I), and flavin reductase (Fre) isolated from Pseudarthrobacter chlorophenolicus A6 and Escherichia coli K-12, respectively. The retained catalytic activity of the enzymes immobilized on Ni-zeolite was as high as 64% of the value for the corresponding free enzymes. The Michaelis-Menten kinetic parameters v_max and K_M of the immobilized enzymes were determined to be 0.20 mM·min^-1 and 0.44 mM, respectively. These results are expected to provide useful information with respect to the development of novel enzymatic treatments for phenolic hydrocarbon contaminants.

Designing and investigation of photo-active gellan gum for the efficient immobilization of catalase by entrapment

A photo-active gellan gum (Gel) derivative was developed by amide bond combination with trans-4-[p-(amino)styryl]pyridine (SP). The SP-Gel was cross-linked by UV curing via the intermolecular 2π + 2π cycloaddition of the inserted SP-CH=CH- moieties. The chemical structure of the obtained photo-crosslinkable biopolymer was investigated before and after the UV curing and the progress of the performed 2π + 2π cycloaddition-based cross-linking was detected via UV-visible light spectra. SP-Gel was evaluated as a polymeric matrix for the immobilization of catalase via entrapment technique. The synthesized biopolymer was mixed with the catalase and molded in the form of membranes that were UV cured to encapsulate the enzyme. The membranes were able to entrap 0.75 mg/cm² with retained activity reached above 95%. The immobilized catalase displayed higher thermal stability and higher resistance toward the environmental pH disturbances compared to the free enzyme. Also, despite the observed lower catalase-H₂O₂ affinity upon the entrapment that was indicated from the performed kinetic studies, the reusability and storage stability experiments revealed the economic value of the entire process by preserving around 95% and 83% of the initial catalase activity after the fifth and tenth operation cycles, respectively.

An accomplished procedure of horseradish peroxidase immobilization for removal of acid yellow 11 in aqueous solutions

Horseradish peroxidase (HRP) characteristics were improved by two techniques, Na-alginate entrapment and glutaraldehyde crosslinking prior to alginate entrapment, in order to enhance the stability, functionality and removal of dyes in waste water. Free, entrapped and crosslinked-entrapped enzymes were compared by activity assays, which indicated the optimum temperature is 25 °C and pH 4.0-5.0. Kinetics results showed that alginate entrapment and crosslinking prior to entrapment increased V_max and did not cause any significant decrease in K_m. The thermal resistance of the free enzyme was short-term, zero residual activity after 250 min, while the immobilized enzymes preserved more than 50% of their activity for 5 h at 60 °C. Immobilized HRP was resistant to methanol, ethanol, DMSO and THF. The storage stability of free HRP ended in 35 days whereas entrapped and crosslinked-entrapped HRPs had 87 and 92% residual activity at the 60th day, respectively. HRP was used in the decolorization of azo dye Acid yellow 11 and total decolorization (>99%) was obtained using crosslinked-entrapped HRP. Reusability studies presented the improvement that crosslinked-entrapped HRP reached 74% decolorization after 10 batches. The results demonstrated that the novel immobilized HRP can be used as an effective catalyst for dye degradation of industrial waste effluents.

Synthesis of Chitosan Beads Incorporating Graphene Oxide/Titanium Dioxide Nanoparticles for In Vivo Studies

Scaffold development for cell regeneration has increased in recent years due to the high demand for more efficient and biocompatible materials. Nanomaterials have become a critical alternative for mechanical, thermal, and antimicrobial property reinforcement in several biopolymers. In this work, four different chitosan (CS) bead formulations crosslinked with glutaraldehyde (GLA), including titanium dioxide nanoparticles (TiO₂), and graphene oxide (GO) nanosheets, were prepared with potential biomedical applications in mind. The characterization of by FTIR spectroscopy, X-ray photoelectron spectroscopy (XRD), thermogravimetric analysis (TGA), energy-dispersive spectroscopy (EDS) and scanning electron microscopy (SEM), demonstrated an efficient preparation of nanocomposites, with nanoparticles well-dispersed in the polymer matrix. In vivo, subdermal implantation of the beads in Wistar rat′s tissue for 90 days showed a proper and complete healing process without any allergenic response to any of the formulations. Masson′s trichrome staining of the histological implanted tissues demonstrated the presence of a group of macrophage/histiocyte compatible cells, which indicates a high degree of biocompatibility of the beads. The materials were very stable under body conditions as the morphometry studies showed, but with low resorption percentages. These high stability beads could be used as biocompatible, resistant materials for long-term applications. The results presented in this study show the enormous potential of these chitosan nanocomposites in cell regeneration and biomedical applications.

Encapsulation of HRP Enzyme onto a Magnetic Fe3O4 Np–PMMA Film via Casting with Sustainable Biocatalytic Activity

Horseradish peroxidase (HRP) enzyme was effectively encapsulated onto an Fe3O4 nanoparticle–polymethyl methacrylate (PMMA) film via the casting method. The HRP was immobilized on the 0.5% Fe3O4Np–PMMA film and characterized by Fourier transform infrared spectroscopy and field emission scanning electron microscopy. Moreover, the reusability, thermal stability, optimum pH, optimum temperature, the influence of metal ions, and the effects of detergent and organic solvent were investigated. After optimizing the immobilization conditions, the highest efficiency of the immobilized enzyme was 88.4% using 0.5% Fe3O4Np–PMMA. The reusability of the immobilized HRP activity was 78.5% of its initial activity after being repeatedly used for 10 cycles. When comparing the free and immobilized forms of the HRP enzyme, changes in the optimum temperature and optimum pH from 30 to 40 °C and 7.0 to 7.5, respectively, were observed. The Km and Vmax for the immobilized HRP were estimated to be 41 mM, 0.89 U/mL for guaiacol and 5.84 mM, 0.66 U/mL for H2O2, respectively. The high stability of the immobilized HRP enzyme was obtained using metal ions, a high urea concentration, isopropanol, and Triton X-100. In conclusion, the applicability of immobilized HRP involves the removal of phenol in the presence of hydrogen peroxide, therefore, it could be a potential catalyst for the removal of wastewater aromatic pollutants.

Enhanced Reusability of Horseradish Peroxidase Immobilized onto Graphene Oxide/Magnetic Chitosan Beads for Cost Effective Cholesterol Oxidase Assay

Background:

Horseradish Peroxidase (HRP) is an important biocatalyst extensively used in enzymatic reactions. Cholesterol oxidase (ChoX) is a commercially valuable enzyme used in the estimation of cholesterol in human serum. ChoX is an oxygen oxidoreductase class of enzyme which catalyzes the oxidation of cholesterol in the presence of O2, liberating hydrogen peroxide H2O2as a by-product. HRP catalyzes the reduction of this H2O2in the presence of a redox dye (chromophore), producing a pink colored Quinoneimine which can be measured spectrophotometrically. The use of soluble HRP makes this assay method expensive for each time use and the recovery of HRP is not possible.

Objective:

Our aim was to prepare the HRP immobilized beads having magnetic properties for the ease of separation and increasing the reusability of HRP for the low cost ChoX assay.

Methods:

In the present work, we prepared magnetic chitosan beads using chitosan-Fe2O3nanoparticle blend coated with Graphene Oxide (GO), and subsequently activated with 2.5% glutaraldehyde (GA). Enzyme loaded beads were characterized by SEM, FTIR, and XRD analysis.

Results:

The immobilization efficiency was ~80% and the immobilized HRP retained 90% of its initial activity up to 12 times reuse. The pH and temperature optima were shifted from 6.5 and 50°C for soluble HRP to 7.0 and 55°C for the immobilized HRP, respectively. Storage stability of immobilized HRP was 93.72% and 60.97% after 30 and 60 days storage respectively, at 4°C.

Conclusion:

On the basis of the present study, the HRP loaded magnetic chitosan/graphene oxide beads could be used for low-cost ChoX assay at laboratory scale due to its enhanced reusability and stability.

Peroxidase Immobilized Cryogels for Phenolic Compounds Removal

In this presented work, preparation of poly(AAm) cryogel, peroxidase immobilization onto the poly(AAm) cryogel, and usability of these enzyme modified cryogels for phenolic compounds removal were described. For this purpose, poly(AAm) cryogels were synthesized by using cryocopolymerization technique at sub-zero temperatures, and covalently functionalized with peroxidase enzyme by EDC/NHS chemistry. Characterization of the cryogels was carried out by FTIR, SEM, and EDX analysis. Maximum peroxidase loading onto poly(AAm) cryogel was found to be as 127.30 mg/g cryogel. Kinetic parameters of free and immobilized peroxidases were also investigated along with the stability tests. Finally, phenolic compounds removal efficiency of the peroxidase immobilized poly(AAm) cryogel was studied towards model phenolics such as phenol, bisphenol A, guaiacol, pyrogallol, and catechol; and very high phenolic removal efficiency was recorded.

InP/ZnS quantum dot-based fluorescent probe for directly sensitive and selective detection of horseradish peroxidase

InP/ZnS quantum dot (QD)-based fluorescent probe for directly sensitive and selective detection of horseradish peroxidase (HRP) was reported herein. Fluorescence of InP/ZnS QDs was statically quenched by HRP, due to the ground state complex formation of InP/ZnS QDs with HRP. Such ground state complex formation between InP/ZnS QDs and HRP reduced both the α-helix content and the melting temperature of HRP. Several key factors including InP/ZnS QDs concentration, buffer pH value, ionic strength, reaction temperature, and reaction time those affected the analytical performance of InP/ZnS QDs in HRP determination were investigated thoroughly. Under the optimal conditions, fluorescence intensity of InP/ZnS QDs was linearly decreased with the increasing of HRP concentration during the range of 1.0 × 10^-9 M ∼ 3.0 × 10^-8 M (0.01 U ml^-1 ∼ 0.3 U ml^-1) with the detection limit as low as 1.2 × 10^-10 M (1.2 mU ml^-1). The present method showed excellent selectivity for HRP over some amino acids, nucleotides, and common proteins. This method was utilized to detect HRP in synthetic samples successfully.

Agarose-chitosan hydrogel-immobilized horseradish peroxidase with sustainable bio-catalytic and dye degradation properties

Herein, we developed and characterized robust agarose-chitosan hydrogel using N‑hydroxysuccinimide (NHS) as a mild chemical cross-linker. The hydrogel offered a simple, effective and eco-friendlier support material with >90% of immobilization efficiency of horseradish peroxidase. The surface morphology and functional properties of the agarose-chitosan hydrogel with and without immobilized horseradish peroxidase were investigated by scanning electron microscopy and Fourier-transform infrared, respectively. The agarose-chitosan hydrogel-immobilized horseradish peroxidase (ACH-HRP) exhibited wide-working pH and temperature stability, and promising reusability for its substrate oxidation. The ACH-HRP preserved a better activity under acidic environments, pH 4.0 (38 vs. 5.9%), and well stabilized under alkaline conditions, retaining a 3.9-folds greater activity than a free counterpart at pH 10. With reference to a free enzyme, 1.6- and 4-fold greater catalytic activity was achieved at 50 and 70 °C, respectively, by the immobilized HRP. Further, the hydrogel displayed insignificant loss in enzyme functionality sustaining above 90% and 60% of original activity after 5 and 10 continuous cycles of use. HPLC profile corroborated the enzyme-assisted Reactive Blue 19 (RB-19) degradation, whereas UPLC/MS analysis scrutinized the dye degradation intermediates and a tentative mechanistic degradation pathway was proposed. In conclusion, the results demonstrate that ACH-HRP is a promising option for use as industrial biocatalyst in diverse biotechnological applications.