An overview of technologies for immobilization of enzymes and surface analysis techniques for immobilized enzymes

Smart Nanoparticles for Selective Immobilization of Acid Phosphatases

An easy to use method combining the selectivity of metal chelate affinity binding with strong covalent linking was developed for immobilization of non-specific acid phosphatases bearing a His-tag from crude cell lysate. Silica nanoparticles were grafted with aminopropyl functions which were partially transformed further with EDTA dianhydride to chelators. The heterofunctionalized nanoparticles charged with Ni2+ as the most appropriate metal ion were applied as support. First, the His-tagged phosphatases were selectively bound to the metal-chelate functions of the support. Then, the enzyme-charged silica nanoparticles were further stabilized by forming a covalent linkage between nucleophilic moieties at the enzyme surface and free amino groups of the support using neopentylglycol diglycidylether as the most effective bifunctional linking agent. The phosphatase biocatalysts obtained by this method exhibited better phosphate transfer activity with a range of alcohols and PPi as phosphate donor in aqueous medium applying batch and continuous-flow modes than the ones immobilized on conventional supports. Furthermore, this novel strategy opens up novel possibility for efficient immobilization of other His-tagged recombinant enzymes.

Alkaline Phosphatase Immobilization on New Chitosan Membranes with Mg2+ for Biomedical Applications

In this paper, we present the fabrication and characterization of new chitosan-based membranes while using a new biotechnology for immobilizing alkaline phosphatase (ALP). This technology involved metal ions incorporation to develop new biopolymeric supports. The chemical structure and morphological characteristics of proposed membranes were evaluated by infrared spectroscopy (FT-IR) and the scanning electron microscopy technique (SEM). The inductively coupled plasma mass spectrometry (ICP-MS) evidenced the metal ion release in time. Moreover, the effect of Mg²⁺ on the enzymatic activity and the antibacterial investigations while using Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacteria, hemolysis, and biocompatibility behavior were studied. Immobilizing ALP into the chitosan membranes composition followed by the incorporation of Mg²⁺ led to polymeric supports with enhanced cellular viability when comparing to chitosan-based membranes without Mg²⁺. The results obtained evidenced promising performance in biomedical applications for the new biopolymeric supports that are based on chitosan, ALP, and metal ions.

Analysis of solute-protein interactions and solute-solute competition by zonal elution affinity chromatography

Many biological processes involve solute-protein interactions and solute-solute competition for protein binding. One method that has been developed to examine these interactions is zonal elution affinity chromatography. This review discusses the theory and principles of zonal elution affinity chromatography, along with its general applications. Examples of applications that are examined include the use of this method to estimate the relative extent of solute-protein binding, to examine solute-solute competition and displacement from proteins, and to measure the strength of these interactions. It is also shown how zonal elution affinity chromatography can be used in solvent and temperature studies and to characterize the binding sites for solutes on proteins. In addition, several alternative applications of zonal elution affinity chromatography are discussed, which include the analysis of binding by a solute with a soluble binding agent and studies of allosteric effects. Other recent applications that are considered are the combined use of immunoextraction and zonal elution for drug-protein binding studies, and binding studies that are based on immobilized receptors or small targets.

Sensors for Fetal Hypoxia and Metabolic Acidosis: A Review

This article reviews existing clinical practices and sensor research undertaken to monitor fetal well-being during labour. Current clinical practices that include fetal heart rate monitoring and fetal scalp blood sampling are shown to be either inadequate or time-consuming. Monitoring of lactate in blood is identified as a potential alternative for intrapartum fetal monitoring due to its ability to distinguish between different types of acidosis. A literature review from a medical and technical perspective is presented to identify the current advancements in the field of lactate sensors for this application. It is concluded that a less invasive and a more continuous monitoring device is required to fulfill the clinical needs of intrapartum fetal monitoring. Potential specifications for such a system are also presented in this paper.

Stabilizing displayed proteins on vegetative Bacillus subtilis cells

Microbes engineered to display heterologous proteins could be useful biotechnological tools for protein engineering, lignocellulose degradation, biocatalysis, bioremediation, and biosensing. Bacillus subtilis is a promising host to display proteins, as this model Gram-positive bacterium is genetically tractable and already used industrially to produce enzymes. To gain insight into the factors that affect displayed protein stability and copy number, we systematically compared the ability of different protease-deficient B. subtilis strains (WB800, BRB07, BRB08, and BRB14) to display a Cel8A-LysM reporter protein in which the Clostridium thermocellum Cel8A endoglucanase is fused to LysM cell wall binding modules. Whole-cell cellulase measurements and fractionation experiments demonstrate that genetically eliminating extracytoplasmic bacterial proteases improves Cel8A-LysM display levels. However, upon entering stationary phase, for all protease-deficient strains, the amount of displayed reporter dramatically decreases, presumably as a result of cellular autolysis. This problem can be partially overcome by adding chemical protease inhibitors, which significantly increase protein display levels. We conclude that strain BRB08 is well suited for stably displaying our reporter protein, as genetic removal of its extracellular and cell wall-associated proteases leads to the highest levels of surface-accumulated Cel8A-LysM without causing secretion stress or impairing growth. A two-step procedure is presented that enables the construction of enzyme-coated vegetative B. subtilis cells that retain stable cell-associated enzyme activity for nearly 3 days. The results of this work could aid the development of whole-cell display systems that have useful biotechnological applications.

Development of a reusable and sustainable biocatalyst by immobilization of soybean peroxidase onto magnetic adsorbent

In this work we synthesized an activated carbon/magnetite composite by a simple co-precipitation method. The activated carbon (AC) was synthesized from the solid waste obtained in the extraction process of the peroxidase enzyme and the magnetic composite was used as support for the immobilization of soybean peroxidase (SP). After the determination of the optimal immobilization parameters, a 100% yield was achieved under the following conditions: support:enzyme proportion of 1.0:0.05 g, equilibration time of 7 h, pH 3.0 (citrate buffer phosphate 0.1 mol L-1) and temperature of 50 °C. The determination of pH to the point of zero charge was also done to assist in the understanding of the immobilization process at different pH values. Several characterization techniques were used, such as thermogravimetric analysis, elemental analysis composition, X-ray powder diffraction, Fourier transform infrared spectroscopy and Scanning electron microscopy. The biocatalyst presented excellent operational stability and was reused for 11 consecutive cycles. The magnetic properties inserted in the AC contributed to the removal of the biocatalyst from the reaction medium without interfering in the adsorptive characteristics of the AC. Thus, the activated carbon/magnetite composite can be applied to different research fields with high performance.

Development and performance of a 3D-printable poly(ethylene glycol) diacrylate hydrogel suitable for enzyme entrapment and long-term biocatalytic applications

Physical entrapment of enzymes within a porous matrix is a fast and gentle process to immobilize biocatalysts to enable their recycling and long-term use. This study introduces the development of a biocompatible 3D-printing material suitable for enzyme entrapment, while having good rheological and UV-hardening properties. Three different viscosity-enhancing additives have been tested in combination with a poly(ethylene glycol) diacrylate-based hydrogel system. The addition of polyxanthan or hectorite clay particles results in hydrogels that degrade over hours or days, releasing entrapped compounds. In contrast, the addition of nanometer-sized silicate particles ensures processability while preventing disintegration of the hydrogel. Lattice structures with a total height of 6 mm consisting of 40 layers were 3D-printed with all materials and characterized by image analysis. Rheological measurements identified a shear stress window of 200 < τ < 500 Pa at shear rates of 25 s^-1 and 25°C for well-defined geometries with an extrusion-based printhead. Enzymes immobilized in these long-term stable hydrogel structures retained an effective activity of approximately 10% compared to the free enzyme in solution. It could be shown that the reduction of effective activity is not caused by a significant reduction of the intrinsic enzyme activity but by mass transfer limitations within the printed hydrogel structures.

Immobilization of ligninolytic enzymes from white-rot fungi in cross-linked aggregates

Ligninolytic enzymes from white-rot fungi are widely used in biotechnological processes. However, the application of these enzymes as free enzymes is limited due to their instability and lack of reusability. Enzyme stabilization is therefore a major challenge in biocatalytic process research, and immobilization methods are desirable. Using cross-linked enzyme aggregates (CLEAs) such as magnetic CLEAs, porous-CLEAs and combi-CLEAs is a promising technique for overcoming these issues. Cross-linking methods can stabilize and immobilize enzymes by interconnecting enzyme molecules via multiple bonds using cross-linking agents such as glutaraldehyde. The high catalyst density and microporous assembly of CLEAs guarantee high catalyst activity, which, together with their long shelf life, operational stability, and reusability, provide a cost-efficient alternative to matrix-assisted immobilization approaches. Here, we review current progress in ligninolytic enzyme immobilization and provide a comprehensive review of CLEAs. Moreover, we summarize the use of these CLEAs for biocatalysis processes, bioremediation such as dye decolourization, wastewater treatment or pharmaceutically active compound elimination.

Functionalized Magnetic Bacterial Cellulose Beads as Carrier for Lecitase® Ultra Immobilization

Bacterial cellulose spheres subjected to amination and inlaid modification with superparamagnetic molecules were analyzed with regard to possibility of their application as an immobilization carrier of Lecitase® Ultra (LU) enzyme. The starting point to obtain the carrier was synthesis of bacterial cellulose spheres performed in shaking cultures of Komagataeibacter xylinus. These spheres were subsequently subjected to a multi-stage modification to increase the efficiency of the immobilization process and to separate product from the reaction medium. Maximal yield of Lecitase® Ultra immobilization equaled 70%. It was also found that immobilization process did not affect the pH and LU temperature optimum. Moreover, immobilized enzyme exhibited similar temperature stability profile as its native form. The immobilization process did not significantly affect the enzyme K_M value. The immobilized enzyme retained over 70% of its initial activity after 8 cycles of use. The immobilized enzyme displayed good storage stability and retained 80% of its initial activity after 4 weeks at 4 °C. The potential application of such modified cellulose-based carrier may be correlated with lower costs of process thanks to higher enzyme’s reusability in comparison to unbound enzyme. Moreover, data presented in the current study may serve as proof of a concept of cellulose-based carrier utilization for immobilization of enzymes other than LU and of high industrial importance.

Encapsulation of the reductase component of p-hydroxyphenylacetate hydroxylase in poly(lactide-co-glycolide) nanoparticles by three different emulsification techniques

p-Hydroxyphenylacetate 3-hydroxylase component 1 (C1) is a useful enzyme for generating reduced flavin and NAD+ intermediates. In this study, poly(lactide-co-glycolide) (PLGA) nanoparticles (NPs) were used to encapsulate the C1 (PLGA-C1 NPs). Enzymatic activity, stability, and reusability of PLGA-C1 NPs prepared using three different methods [oil in water (o/w), water in oil in water (w/o/w), and solid in oil in water (s/o/w)] were compared. The s/o/w provided the optimal conditions for encapsulation of C1(PLGA-C1,s NPs), giving the highest enzyme activity, stability, and reusability. The s/o/w method improves enzyme activity ∼11 and 9-fold compared to w/o/w (PLGA-C1,w NPs) and o/w (PLGA-C1,o NPs). In addition, s/o/w prepared PLGA-C1,s NPs could be reused 14 times with nearly 50% activity remaining, a much higher reusability compared to PLGA-C1,o NPs and PLGA-C1,w NPs. These nanovesicles were successfully utilised to generate reduced flavin mononucleotide (FMN) and supply this cofactor to a hydroxylase enzyme that has application for synthesising anti-inflammatory compounds. Therefore, this recycling biocatalyst prepared using the s/o/w method is effective and has the potential for use in combination with other enzymes that require reduced FMN. Application of PLGA-C1,s NPs may be possible in additional biocatalytic processes for chemical or biochemical production.

Influence of Three Commercial Graphene Derivatives on the Catalytic Properties of a Lactobacillus plantarum α-l-Rhamnosidase When Used as Immobilization Matrices

The modification of carbon nanomaterials with biological molecules paves the way toward their use in biomedical and biotechnological applications, such as next-generation biocatalytic processes, development of biosensors, implantable electronic devices, or drug delivery. In this study, different commercial graphene derivatives, namely, monolayer graphene oxide (GO), graphene oxide nanocolloids (GOCs), and polycarboxylate-functionalized graphene nanoplatelets (GNs), were compared as biomolecule carrier matrices. Detailed spectroscopic analyses showed that GO and GOC were similar in composition and functional group content and very different from GN, whereas divergent morphological characteristics were observed for each nanomaterial through microscopy analyses. The commercial α-l-rhamnosidase RhaB1 from the probiotic bacterium Lactobacillus plantarum, selected as a model biomolecule for its relevant role in the pharma and food industries, was directly immobilized on the different materials. The binding efficiency and biochemical properties of RhaB1-GO, RhaB1-GOC, and RhaB1-GN composites were analyzed. RhaB1-GO and RhaB1-GOC showed high binding efficiency, whereas the enzyme loading on GN, not tested in previous enzyme immobilization studies, was low. The enzyme showed contrasting changes when immobilized on the different material supports. The effect of pH on the activity of the three RhaB1-immobilized versions was similar to that observed for the free enzyme, whereas the activity-temperature profiles and the response to the presence of inhibitors varied significantly between the RhaB1 versions. In addition, the apparent K_m for the immobilized and soluble enzymes did not change. Finally, the free RhaB1 and the immobilized enzyme in GOC showed the best storage and reutilization stability, keeping most of their initial activity after 8 weeks of storage at 4 °C and 10 reutilization cycles, respectively. This study shows, for the first time, that distinct commercial graphene derivatives can influence differently the catalytic properties of an enzyme during its immobilization.

Nano-Biocatalysts of Cyt c@ZIF-8/GO Composites with High Recyclability via a de Novo Approach

To improve the stability and recyclability of enzymes immobilized on metal-organic frameworks (MOFs), graphene oxide (GO) with surface oxygen-rich functional groups was selected to form ZIF-8/GO nanocomposites with the zeolitic imidazolate framework (ZIF-8) for cytochrome c (Cyt c) immobilization. It was found that the functional groups on the GO surface were involved in the growth of ZIF-8 without affecting the crystal structure but their particle size was reduced to about 200 nm. The storage stability and resistance to organic solvents of Cyt c were obviously improved after the immobilization on the ZIF-8/GO nanocomposite. On one hand, compared with Cyt c@ZIF-8 and Cyt c@GO with 30 and 60% protein leakage, Cyt c@ZIF-8/GO displayed little protein leakage after 60 h of storage. On the other hand, Cyt c@ZIF-8/GO retained a residual activity of approximately 100% after being stored in ethanol and acetone for 2 h, whereas the free enzyme, Cyt c@ZIF-8, and Cyt c@GO retained only about 10, 50, and 40%, respectively. In addition, the Cyt c@ZIF-8/GO nanocomposites can be utilized up to four cycles with virtually no loss of activity and may be further applied on H₂O₂ biosensing systems. The synergistic effect between MOFs and GO in ZIF-8/GO nanocomposites provides infinite possibilities as immobilized enzyme carriers.

Controlling Redox Enzyme Orientation at Planar Electrodes

Redox enzymes, which catalyze reactions involving electron transfers in living organisms, are very promising components of biotechnological devices, and can be envisioned for sensing applications as well as for energy conversion. In this context, one of the most significant challenges is to achieve efficient direct electron transfer by tunneling between enzymes and conductive surfaces. Based on various examples of bioelectrochemical studies described in the recent literature, this review discusses the issue of enzyme immobilization at planar electrode interfaces. The fundamental importance of controlling enzyme orientation, how to obtain such orientation, and how it can be verified experimentally or by modeling are the three main directions explored. Since redox enzymes are sizable proteins with anisotropic properties, achieving their functional immobilization requires a specific and controlled orientation on the electrode surface. All the factors influenced by this orientation are described, ranging from electronic conductivity to efficiency of substrate supply. The specificities of the enzymatic molecule, surface properties, and dipole moment, which in turn influence the orientation, are introduced. Various ways of ensuring functional immobilization through tuning of both the enzyme and the electrode surface are then described. Finally, the review deals with analytical techniques that have enabled characterization and quantification of successful achievement of the desired orientation. The rich contributions of electrochemistry, spectroscopy (especially infrared spectroscopy), modeling, and microscopy are featured, along with their limitations.

Design of epoxy-functionalized Fe3O4@MCM-41 core-shell nanoparticles for enzyme immobilization

The scope of our research was to prepare the organosilane-modified Fe₃O₄@MCM-41 core-shell magnetic nanoparticles, used for L-ASNase immobilization and explored screening of immobilization conditions such as pH, temperature, thermal stability, kinetic parameters, reusability and storage stability. In this content, Fe₃O₄ core-shell magnetic nanoparticles were prepared via co-precipitation method and coated with MCM-41. Then, Fe₃O₄@MCM-41 magnetic nanoparticles were functionalized by (3-glycidyloxypropyl) trimethoxysilane (GPTMS) as an organosilane compound. Subsequently, L-ASNase was covalently immobilized on epoxy-functionalized Fe₃O₄@MCM-41 magnetic nanoparticles. The immobilized L-ASNase had greater activity at high pH and temperature values. It also maintained >92% of the initial activity after incubation at 55 °C for 3 h. Regarding kinetic values, immobilized L-ASNase showed a higher Vmax and lower Km compared to native L-ASNase. In addition, it displayed excellent reusability for 12 successive cycles. After 30 days of storage at 4 °C and 25 °C, immobilized L-ASNase retained 54% and 26% of its initial activities while native L-ASNase lost about 68% and 84% of its initial activity, respectively. As a result, the immobilization of L-ASNase onto magnetic nanoparticles may provide an advantage in terms of removal of L-ASNase from reaction media.

Preparation of Stable Cross-Linked Enzyme Aggregates (CLEAs) of a Ureibacillus thermosphaericus Esterase for Application in Malathion Removal from Wastewater

In this study, the active and stable cross-linked enzyme aggregates (CLEAs) of the thermostable esterase estUT1 of the bacterium Ureibacillus thermosphaericus were prepared for application in malathion removal from municipal wastewater. Co-expression of esterase with an E. coli chaperone team (KJE, ClpB, and ELS) increased the activity of the soluble enzyme fraction up to 200.7 ± 15.5 U mg−1. Response surface methodology (RSM) was used to optimize the preparation of the CLEA-estUT1 biocatalyst to maximize its activity and minimize enzyme loss. CLEA-estUT1 with the highest activity of 29.4 ± 0.5 U mg−1 (90.6 ± 2.7% of the recovered activity) was prepared with 65.1% (w/v) ammonium sulfate, 120.6 mM glutaraldehyde, and 0.2 mM bovine serum albumin at 5.1 h of cross-linking. The biocatalyst has maximal activity at 80 °С and pH 8.0. Analysis of the properties of CLEA-estUT1 and free enzyme at 50–80 °C and pH 5.0–10.0 showed higher stability of the biocatalyst. CLEA-estUT1 showed marked tolerance against a number of chemicals and high operational stability and activity in the reaction of malathion hydrolysis in wastewater (up to 99.5 ± 1.4%). After 25 cycles of malathion hydrolysis at 37 °С, it retained 55.2 ± 1.1% of the initial activity. The high stability and reusability of CLEA-estUT1 make it applicable for the degradation of insecticides.

Multienzyme immobilized polymeric membrane reactor for transformation of lignin model compound

We have developed a multienzyme functionalized membrane reactor for bioconversion of lignin model compound involving enzymatic catalysis. Layer-by-layer approach was used to immobilize three different enzymes (glucose oxidase, peroxidase and laccase) into pH-responsive membranes. This novel membrane reactor couples the in situ generation of hydrogen peroxide (by glucose oxidase) to oxidative conversion of a lignin model compound, guaiacylglycerol-B-guaiacylether (GGE). Preliminary investigation of the efficacy of these functional membranes towards GGE degradation is demonstrated under convective flow mode. Over 90% of the initial feed could be degraded with the multienzyme immobilized membranes at a residence time of approximately 22 seconds. GGE conversion product analysis revealed formation of oligomeric oxidation products with peroxidase, which might be potential hazard to membrane bioreactors. These oxidation products could be further degraded by laccase enzymes in the multienzymatic membranes explaining the potential of multienzyme membrane reactors. The multienzyme incorporated membrane reactors were active for about a month time of storage at 4 °C, and retention of activity was demonstrated after repetitive use.

Rice bran nanofiber composites for stabilization of phytase

This study explores the potential application of rice bran (agro waste) to nano-encapsulate phytase, which is a thermally unstable biologically active enzyme. Rice bran was converted to nanofibers (20–50 nm in diameter) using electrospinning. After optimizing the pH, viscosity, voltage and the distance between electrodes for electrospinning, phytase enzyme was encapsulated and the fibers were cross-linked using sodium tripolyphosphate. Thermal stability of phytase enzyme was improved by 90 °C when they are encapsulated and cross-linked with sodium tripolyphosphate. The activity of the phytase enzyme was monitored at different temperatures. The activity of the pure enzyme was lost at 80 °C while the enzyme encapsulated into nanofibers demonstrated the activity up to 170 °C. This study opens up many opportunities for nanotechnology value addition to many waste materials and also to improve the properties of a range of biomaterials through a sustainable approach.

The performance of immobilized Candida rugosa lipase on various surface modified graphene oxide nanosheets

In this study, we have reported the synthesis of graphene oxide nanosheets (GON) and its functionalization with 2, 4, 6-trichloro-1, 3, 5-triazine (TCT) through two routes, (a) directly reaction of GON with TCT (GON-1), and (b) reaction of GON with pre-functionalized TCT with 3-aminopropyltriethoxysilane (APTS) (GON-2). Subsequently, GON, GON-1 and GON-2 have been used as supports for immobilization of Candida rugosa lipase (CRL). Several techniques such as XRD, SEM, EDS, UV-Vis, CHNS, FTIR and AFM were applied to characterize the nano-structures and success of synthesis, functionalization and CRL immobilization processes. The results corresponding to optimization of immobilization process revealed the following order for values of loading capacity, immobilization yield and leaching of CRL: GON > GON-1 > GON-2, while this order is reversed for, specific activity and recovery activity. The assessment of operational parameters represents the high storage stability and reasonable reusability for all the immobilized CRL while the pH and thermal stability of CRL@GON-2 are higher than two others. It seems the longer linker of GON-2 could more effectively prevent the unfavorable interaction between enzyme-enzyme and enzyme-product that consequently resulted the best catalytic performance, pH and thermal stability. The advantages of these supports make them suitable candidates for practical applications.

Ultrasensitive Determination of Malathion Using Acetylcholinesterase Immobilized on Chitosan-Functionalized Magnetic Iron Nanoparticles

A renewable, disposable, low cost, and sensitive sensor for the detection of organophosphorus pesticides was constructed by immobilizing the acetylcholinesterase enzyme (AChE), via glutaraldehyde, on magnetic iron nanoparticles (Fe₃O₄) previously synthesized and functionalized with chitosan (CS). The sensor was denoted AChE/CS/Fe₃O₄. The magnetic nanoparticles were characterized by Fourier transform infrared spectroscopy and transmission electron microscopy. Acetylthiocholine (ATCh) was incubated with AChE/CS/Fe₃O₄ and attached to a screen-printed electrode using a magnet. The oxidation of thiocholine (from ATCh hydrolysis) was monitored at an applied potential of +0.5 V vs. Ag/AgCl(KCl_sat) in 0.1 mol L⁻¹ phosphate buffer solution (pH 7.5) as the supporting electrolyte. A mixture of the pesticide malathion and ATCh was investigated using the same procedure, and the results were compared and expressed as inhibition percentages. For determination of malathion, the proposed sensor presented a linear response in the range from 0.5 to 20 nmol L⁻¹ (R = 0.9942). The limits of detection (LOD) and quantification (LOQ) were 0.3 and 0.8 nmol L⁻¹, respectively. Real samples were also investigated, with recovery values of 96.0% and 108.3% obtained for tomato and pond water samples, respectively. The proposed sensor is a feasible option for malathion detection, offering a linear response, good sensitivity, and a low detection limit.

Hydrogen-Borrowing Alcohol Bioamination with Coimmobilized Dehydrogenases

The amination of alcohols is an important transformation in chemistry. The redox-neutral (i.e., hydrogen-borrowing) asymmetric amination of alcohols is enabled by the combination of an alcohol dehydrogenase (ADH) with an amine dehydrogenase (AmDH). In this work, we enhanced the efficiency of hydrogen-borrowing biocatalytic amination by co-immobilizing both dehydrogenases on controlled porosity glass FeIII ion-affinity beads. The recyclability of the dual-enzyme system was demonstrated (5 cycles) with total turnover numbers of >4000 and >1000 for ADH and AmDH, respectively. A set of (S)-configured alcohol substrates was aminated with up to 95% conversion and >99%ee (R). Preparative-scale amination of (S)-phenylpropan-2-ol resulted in 90% conversion and 80% yield of the product in 24 h.

Immobilization of laccase onto porous polyvinyl alcohol/halloysite hybrid beads for dye removal

Laccase was immobilized in polyvinyl alcohol beads containing halloysite nanotubes (PVA/HNTs) to improve the stability and reusability of enzyme. The porous structure of PVA/HNTs beads facilitates the entrapment of enzyme and prevents the leaching of immobilized laccase as well. Halloysite nanotubes act as bridge to connect the adjacent pores, facilitating the electron transfer and enhancing the mechanical properties. PVA/HNTs beads have high laccase immobilization capacity (237.02 mg/g) and activity recovery yield (79.15%), indicating it can be used as potential support for laccase immobilization. Compared with free laccase, the immobilized laccase on hybrid beads exhibits enhanced pH tolerance (even at pH 8.0), good thermal stability (57.5% of the initial activity can be maintained at 75 °C), and excellent storage stability (81.17% of enzyme activity could be retained after storage at 4 °C for 5 weeks compared with that for free enzyme of 60%). Also, the removal efficiency for reactive blue can reach as high as 93.41% in the presence of redox mediator 2,2-azinobis(3-ethylbenzthiazoline-6-sulfonate), in which adsorption and degradation exist simultaneously. The remarkable pH tolerance, thermal and storage stability, and reuse ability imply potential application of porous PVA/HNTs immobilized enzyme in environmental fields.

Affinity induced immobilization of adenylate cyclase from the crude cell lysate for ATP conversion

The development of an orientation immobilization technique via affinity between polyhistidine tags and metal ions aims at maintaining biocatalytic activity of the enzymes. In this work, to tackle the issue of the immobilization of adenylate cyclase (AC), a simple and effective approach of synthesizing iminodiacetic acid (IDA)-Ni²⁺ particles was applied for simultaneously purifying and immobilizing his-tagged AC. We chose agarose particles as carriers, and then decorated them with IDA, leading to the formation of a coordination combination of Ni²⁺. The porous carriers with a large pore size of 50 nm and a specific surface area of 45.8 m²/g exhibited favorable enzymatic activity and loading capacity. The optimal pH of the immobilized enzyme increased from 8.0 to 9.0 and the optimal temperature increased from 30 °C to 35 °C, compared to the free AC. Moreover, the immobilized AC retained a residual activity of approximately 80% after storing it at 25 °C for 48 h, whereas only 40% of the activity was left in the free AC at the same conditions. Maximum yield of cyclic adenosine-3', 5'- monophosphate (cAMP) reached up to the summit of the reaction. The immobilized AC by affinity adsorption will provide a promising route for the industrial production of cAMP.

Immobilisation of phytase producing Gluconacetobacter with bacterial cellulose nano‐fibres and promotion of enzyme activities by magnetite nanoparticles

The isolated Gluconacetobacter sp. with accession number: KY996741 was assayed for evaluation of phytase activity. It could solubilise sodium phytate in the absence of soluble phosphate with the cells; however, the enzyme was not seen in cell free extract, to the best of their knowledge the intracellular phytase activities of Gluconacetobacter sp. was not reported previously. Also, the potential of in situ immobilisation of cells produced enzyme (/phytase producing bacteria) in bacterial cellulose was investigated and was studied by SEM and AFM. The results showed that the immobilised probiotic cells had the best activity of 1229 U/ml. The optimum temperature of the immobilised enzyme activity was at 45°C (5969 U/ml) and the immobilised phytase maintained 64% of its activities after two repeated cycles. The enzyme needs mild conditions for its activity and has a short life time and low stability and lost activities from 1229 to 500 U/ml during 30 days. However, it was showed that the addition of 1 ppm nano‐ferric oxide particles could promote the phytase activities of immobilised cell from 500 U/ml to >1500 U/ml. This immobilised phytase producing cells on bacterial cellulose can be useful as food and/feed supplement for phytin removal.