Activation of Inert Supports for Enzyme(s) Immobilization Harnessing Biocatalytic Sustainability for Perennial Utilization

Although Nature's evolution and intelligence have gifted humankind with noteworthy enzyme candidates to simplify complex reactions with ultrafast, overselective, effortless, mild biological reactions for millions of years, their availability at minute-scale, short-range time-temperature stability, and purification costs hardly justify recycling/or reuse. Covalent immobilization, particularly via multipoint bonds, prevents denaturing, maintains activities for long-range time, pH, and temperature, and makes catalysts available for repetitive usages; which attracts researchers and industries to bring more immobilized enzyme contenders in science and commercial progressions. Inert-support activation, the most crucial step, needs appropriate activators; under mild conditions, the activator's functional group(s) still present on the activated support rapidly couples the enzyme, preventing unfolding and keeping the active site alive. This review summarizes exciting experimental advances, from the 1950s until today, in the activation strategies of various inert supports with five different surface activators, the cyanogen bromide, the isocyanate/isothiocyanate, the glutaraldehyde, the carbodiimide (with or without N-hydroxysuccinimide (NHS)), and the diazo group, for the immobilization of diverse enzymes for broader applications. These activators under mild pH (7.5 ± 0.5) and temperature (27 ± 3 °C) and ordinary stirring witnessed support activation and enzyme coupling and put off unfolding, harnessing addressable activities (CNBr: 40 ± 10%; -N═C═O/-N═C═S: 32 ± 7%; GA: 70 ± 15%; CDI: 60 ± 10%; -N+≡N: 80 ± 15%), while underprivileged stability, longevity, and reusabilities keep future investigations alive.

Controlled Primary Amine-Enriched SG-Bonded Papain Surface: Synthesis, Characterization, and Extraction of Protonated Dichromate

The single-step synthesis of nitro-derivatized SG using dimethyldichlorosilane in an aprotic solvent dichloromethane at 300 K is efficient and straightforward. Reduction and diazotization effectively functionalize the material for enzyme coupling at the O-carbon of the enzyme's tyrosine. The high extraction efficiency of protonated dichromate ions with a breakthrough capacity of 480 μmol·g-1 is notable. Eco-friendly elution using distilled water achieves a significant enrichment factor of 23.2. Excellent reusability (up to 900 cycles) and stable sorption efficiency (ζ ≥ 0.9) highlight the material's potential for practical applications and future research.

Chemically Bonded Pepsin via Its Inert Center to Diazo Functionalized Silica Gel through Multipoint Attachment Mode: A Way of Restoring Biocatalytic Sustainability over "Wider pH" Range

Proteolytic enzymes play a pivotal role in the industry. Still, because of denaturation, the extensive applicability at their level of best catalytic efficiency over a more comprehensive pH range, particularly in alkaline conditions over pH 8, has not been fully developed. On the other hand, enzyme immobilization following a suitable protocol is a long pending issue that determines the conformational stability, specificity, selectivity, enantioselectivity, and activity of the native enzymes at long-range pH. As a bridge between these two findings, in an attempt at a freezing temperature 273-278 K at an alkaline pH, the diazo-functionalized silica gel (SG) surface has been used to rapidly diazo couple pepsin through its inert center, the O-carbon of the phenolic -OH of surface-occupied Tyr residues in a multipoint mode: when all the various protein groups, viz., amino, thiol, phenol, imidazole, carboxy, etc., in the molecular sequence including those belonging to the active sites, remain intact, the inherent inbuilt interactions among themselves remain. Thereby, the macromolecule's global conformation and helicity preserve the status quo. The dimension of the SG-enzyme conjugate confirms as {Si(OSi)4 (H2O)1.03}n {-O-Si(CH3)2-O-C6H4-N═N+}4·{pepsin}·yH2O; where the values of n and y have been determined respectively as 347 and 188. The material performs the catalytic activity much better at 7-8.5 than at pH 2-3.5 and continues for up to six months without any appreciable change.

Optimization of Alpha-Amylase Production by a Local Bacillus paramycoides Isolate and Immobilization on Chitosan-Loaded Barium Ferrite Nanoparticles

We set out to isolate alpha-amylase producers from soil samples, optimize the production, and immobilize the enzyme on chitosan-loaded barium ferrite nanoparticles (CLBFNPs). Alpha-amylase producers were isolated on starch agar plates and confirmed by dinitrosalicylic acid assay. The potent isolate was identified by phenotypic methods, 16S-rRNA sequencing, and phylogenetic mapping. Sequential optimization of α-amylase production involved the use of Plackett–Burman (P–BD) and central composite designs (CCD), in addition to exposing the culture to different doses of gamma irradiation. Alpha-amylase was immobilized on CLBFNPs, and the nanocomposite was characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy, with energy-dispersive analysis of X-ray analysis. Forty-five α-amylase producers were isolated from 100 soil samples. The highest activity (177.12 ± 6.12 U/mg) was detected in the MS009 isolate, which was identified as Bacillus paramycoides. The activity increased to 222.3 ± 5.07 U/mg when using the optimal culture conditions identified by P–BD and CCD, and to 319.45 ± 4.91 U/mg after exposing the culture to 6 kGy. Immobilization of α-amylase on CLBFNPs resulted in higher activity (246.85 ± 6.76 U/mg) compared to free α-amylase (222.254 ± 4.89 U/mg), in addition to retaining activity for up to five cycles of usage. Gamma irradiation improved α-amylase production, while immobilization on CLBFNPs enhanced activity, facilitated enzyme recovery, and enabled its repetitive use.

Effective utilization of magnetic nano-coupled cloned β-xylanase in saccharification process

The β-xylanase gene (DCE06_04615) with 1041 bp cloned from Thermotoga naphthophila was expressed into E. coli BL21 DE3. The cloned β-xylanase was covalently bound to iron oxide magnetic nanoparticles coated with silica utilizing carbodiimide. The size of the immobilized MNPs (50 nm) and their binding with β-xylanase were characterized by Fourier-transform electron microscopy (FTIR) (a change in shift particularly from C–O to C–N) and transmission electron microscopy (TEM) (spherical in shape and 50 nm in diameter). The results showed that enzyme activity (4.5 ± 0.23 U per mL), thermo-stability (90 °C after 4 hours, residual activity of enzyme calculated as 29.89% ± 0.72), pH stability (91% ± 1.91 at pH 7), metal ion stability (57% ± 1.08 increase with Ca²⁺), reusability (13 times) and storage stability (96 days storage at 4 °C) of the immobilized β-xylanase was effective and superior. The immobilized β-xylanase exhibited maximal enzyme activity at pH 7 and 90 °C. Repeated enzyme assay and saccharification of pretreated rice straw showed that the MNP-enzyme complex exhibited 56% ± 0.76 and 11% ± 0.56 residual activity after 8 times and 13 times repeated usage. The MNP-enzyme complex showed 17.32% and 15.52% saccharification percentage after 1^st and 8^th time usage respectively. Immobilized β-xylanase exhibited 96% residual activity on 96 days' storage at 4 °C that showed excellent stability.

The β-xylanase gene (DCE06_04615) with 1041 bp cloned from Thermotoga naphthophila was expressed into E. coli BL21 DE3.

Stabilization of enzymes via immobilization: Multipoint covalent attachment and other stabilization strategies

The use of enzymes in industrial processes requires the improvement of their features in many instances. Enzyme immobilization, a requirement to facilitate the recovery and reuse of these water-soluble catalysts, is one of the tools that researchers may utilize to improve many of their properties. This review is focused on how enzyme immobilization may improve enzyme stability. Starting from the stabilization effects that an enzyme may experience by the mere fact of being inside a solid particle, we detail other possibilities to stabilize enzymes: generation of favorable enzyme environments, prevention of enzyme subunit dissociation in multimeric enzymes, generation of more stable enzyme conformations, or enzyme rigidification via multipoint covalent attachment. In this last point, we will discuss the features of an "ideal" immobilization protocol to maximize the intensity of the enzyme-support interactions. The most interesting active groups in the support (glutaraldehyde, epoxide, glyoxyl and vinyl sulfone) will be also presented, discussing their main properties and uses. Some instances in which the number of enzyme-support bonds is not directly related to a higher stabilization will be also presented. Finally, the possibility of coupling site-directed mutagenesis or chemical modification to get a more intense multipoint covalent immobilization will be discussed.

Catalytic and antimicrobial properties of α-amylase immobilised on the surface of metal oxide nanoparticles

New methods of obtaining products containing enzymes reduce the costs associated with obtaining them, increase the efficiency of processes and stabilize the created biocatalytic systems. In the study a catalytic system containing the enzyme α-amylase immobilized on ZnO nanoparticle and Fe3O4 nanoparticles was created. The efficiency of the processes was obtained with variables: concentrations of enzymes, temperatures and times, to define the best conditions for running the process, for which were determined equilibrium and kinetics of adsorption. The most effective parameters of α-amylase immobilization on metal oxides were determined, obtaining 100.8 mg/g sorption capacity for ZnO and 102.9 mg/g for Fe3O4 nanoparticles. Base on the best parameters, ZnO-α-amylase was investigated as an antimicrobial agent and Fe3O4-α-amylase was tested as a catalyst in the process of starch hydrolysis. As a result of the conducted experiments, it was found that α-amylase immobilized on Fe3O4 nanoparticles maintained high catalytic activity (the reaction rate constant KM = 0.7799 [g/dm3] and the maximum reaction rate Vmax = 8.660 [g/(dm3min)]).