Enzyme immobilization on activated carbon: alleviation of enzyme deactivation by hydrogen peroxide

Sources, purification, immobilization and industrial applications of microbial lipases: An overview

Microbial lipase is looking for better attention with the fast growth of enzyme proficiency and other benefits like easy, cost-effective, and reliable manufacturing. Immobilized enzymes can be used repetitively and are incapable to catalyze the reactions in the system continuously. Hydrophobic supports are utilized to immobilize enzymes when the ionic strength is low. This approach allows for the immobilization, purification, stability, and hyperactivation of lipases in a single step. The diffusion of the substrate is more advantageous on hydrophobic supports than on hydrophilic supports in the carrier. These approaches are critical to the immobilization performance of the enzyme. For enzyme immobilization, synthesis provides a higher pH value as well as greater heat stability. Using a mixture of immobilization methods, the binding force between enzymes and the support rises, reducing enzyme leakage. Lipase adsorption produces interfacial activation when it is immobilized on hydrophobic support. As a result, in the immobilization process, this procedure is primarily used for a variety of industrial applications. Microbial sources, immobilization techniques, and industrial applications in the fields of food, flavor, detergent, paper and pulp, pharmaceuticals, biodiesel, derivatives of esters and amino groups, agrochemicals, biosensor applications, cosmetics, perfumery, and bioremediation are all discussed in this review.

Enzyme-Functionalized Cellulose Beads as a Promising Antimicrobial Material

The extensive use of antibiotics over the last decades is responsible for the emergence of multidrug-resistant (MDR) microorganisms that are challenging health care systems worldwide. The use of alternative antimicrobial materials could mitigate the selection of new MDR strains by reducing antibiotic overuse. This paper describes the design of enzyme-based antimicrobial cellulose beads containing a covalently coupled glucose oxidase from Aspergillus niger (GOx) able to release antimicrobial concentrations of hydrogen peroxide (H₂O₂) (≈ 1.8 mM). The material preparation was optimized to obtain the best performance in terms of mechanical resistance, shelf life, and H₂O₂ production. As a proof of concept, agar inhibition halo assays (Kirby-Bauer test) against model pathogens were performed. The two most relevant factors affecting the bead functionalization process were the degree of oxidation and the pH used for the enzyme binding process. Slightly acidic conditions during the functionalization process (pH 6) showed the best results for the GOx/cellulose system. The functionalized beads inhibited the growth of all the microorganisms assayed, confirming the release of sufficient antimicrobial levels of H₂O₂. The maximum inhibition efficiency was exhibited toward Pseudomonas aeruginosa (P. aeruginosa) and Escherichia coli (E. coli), although significant inhibitory effects toward methicillin-resistant Staphylococcus aureus (MRSA) and S. aureus were also observed. These enzyme-functionalized cellulose beads represent an inexpensive, sustainable, and biocompatible antimicrobial material with potential use in many applications, including the manufacturing of biomedical products and additives for food preservation.

Common causes of glucose oxidase instability in in vivo biosensing: a brief review

Clinical management of diabetes must overcome the challenge of in vivo glucose sensors exhibiting lifetimes of only a few days. Limited sensor life originates from compromised enzyme stability of the sensing enzyme. Sensing enzymes degrade in the presence of low molecular weight materials (LMWM) and hydrogen peroxide in vivo. Sensing enzymes could be made to withstand these degradative effects by (1) stabilizing the microenvironment surrounding the sensing enzyme or (2) improving the structural stability of the sensing enzyme genetically. We review the degradative effect of LMWM and hydrogen peroxide on the sensing enzyme glucose oxidase (GOx). In addition, we examine advances in stabilizing GOx against degradation using hybrid silica gels and genetic engineering of GOx. We conclude molecularly engineered GOx combined with silica-based encapsulation provides an avenue for designing long-term in vivo sensor systems.

Immobilization of glucoamylase and glucose oxidase in activated carbon: effects of particle size and immobilization conditions on enzyme activity and effectiveness

Glucoamylase and glucose oxidase have been immobilized on carbodiimide-treated activated carbon particles of various sizes. Loading data indicate nonuniform distribution of immobilized enzyme within the porous support particles. Catalysts with different enzyme loading and overall activities have been prepared by varying enzyme concentration in the immobilizing solution. Analysis of these results by a new method based entirely upon experimentally observable catalyst properties indicates that intrinsic catalytic activity is reduced by immobilization of both enzymes. Immobilized glucoamylase intrinsic activity decreases with increasing enzyme loading, and similar behavior is suggested by immobilized glucose oxidase data analysis. The overall activity data interpretation method should prove useful in other immobilized enzyme characterization research, especially in situations where the intraparticle distribution of immobilized enzyme is nonuniform and unknown.

In vitro and in vivo degradation of glucose oxidase enzyme used for an implantable glucose biosensor

BACKGROUND

The degradation of the glucose oxidase (GOD) enzyme, commonly used in the construction of glucose sensors has been of concern for scientists for decades. Many researchers have found that GOD deactivates over time, mostly due to H2O2 oxidation. This decay can lead to the eventual failure of the sensor. However, these findings are controversial, because other researchers did not find this degradation.

METHODS

The goal of this study was twofold. The first goal was to evaluate the in vitro and in vivo stability of two commercially available GOD enzymes and the second goal was to evaluate Nafion as a protective coating of GOD. Crosslinked GOD samples were sandwiched between two 10-microm pore polycarbonate membranes (Nafion coated or uncoated) and placed in custom designed Lexan chambers. Chambers were then exposed to a total of five different environments: Dulbecco's Modified Eagle Medium (DMEM) or phosphate buffered saline (PBS) with and without a 5.6-mM glucose concentration, as well as the subcutaneous in vivo environment of 12 rats. After a period of up to 4 weeks, chambers were retrieved, opened, and tested for enzyme activity using a three-electrode system.

RESULTS

Enzyme activity showed only a slight decrease when exposed to DMEM and PBS without glucose. A more dramatic decrease in activity was observed in enzymes exposed to PBS and DMEM with 5.6 mM glucose. The in vivo environment also caused a significant decrease in enzyme activity, but the decrease was lower than for the in vitro environment with glucose conditions.

CONCLUSION

The presence of glucose in vitro and in vivo led to the production of H2O2, suggesting this to be the main agent responsible for enzyme degradation. The use of a Nafion coating did not provide any additional protection.

In vivo and in vitro deactivation rates of PTFE-coupled glucose oxidase

The deactivation of immobilized enzymes is a major lifetime limiting factor in several types of potentially implantable biosensors. The deactivation rate of covalently immobilized glucose oxidase was examined in vitro in mock physiologic environments and in the peritoneal cavity of mice. A first order deactivation model describes the observed exponential decay of the enzyme. Deactivation rate constants ranging from 0.198 to 1.3 per day were measured depending on experimental conditions. Enzymes immobilized on PTFE (Teflon) substrates in the peritoneal cavity of mice exhibited greater catalytic lifetimes than control samples kept in glucose solution in vitro.

Effect of substrate presoaking treatment of support materials on the activity of immobilized glucoamylase

The activity of immobilized glucoamylase was remarkably increased by presoaking treatment of the supports in soluble starch solution. Pig bone (PB) particles-100 showed the largest substrate presoaking effect among some representative support materials, increasing the activity of immobilized glucoamylase by 10 times. The improvement in the activity was due to the increase in the specific activity of immobilized proteins. In order to get sufficient substrate presoaking effect, a rapid crosslinking treatment of the enzyme and the substrate-presoaked support was required. The glucoamylase immobilized on PB sheet was very stable and gave a high starch hydrolysis of DE95 (dextrose equivalent) for about 1 month in continuous process.

Immobilization of enzymes on activated carbon: selection and preparation of the carbon support

Based upon its superior catalytic activity for H2O2 decomposition, a bituminous coal-based activated carbon was selected for investigations of pretreatment and enzyme immobilization methods. Pretreatments considered include acid washing, exposure to strong oxidizing agents, contact with concentrated peroxide solutions, nitration and amination, isothiocyanate derivatization, silanization, and stearic acid coating. Effects of these pretreatments on morphology and trace-metal content of the carbon pellets have been studied using scanning electron microscopy and dispersive analysis of x rays. Immobilization of glucoamylase by adsorption, glutaraldehyde crosslinking, and covalent attachment to carbon activated by water-soluble diimide or diazotization have been examined. These different enzyme-carbon catalysts have been characterized by their enzyme loading, enzyme activity, catalytic activity for H2O2 decomposition, or combinations of these measures of performance.

Applications of purification reactions for minimizing reaction-generated enzyme poisoning

A mathematical model has been employed to examine the interplay of reaction and mass transfer in immobilized enzyme systems involving reaction-generated enzyme poisions. Deactivation rates can be significantly reduced in some cases by catalyzing a purification reaction in which the poison is transformed into an innocuous substance. This conclusion in illustrated experimentally for reaction-generated H2O2 in a continuous-flow stirred slurry reactor containing glucose oxidase immobilized on activated carbon.