Influence of silica-derived nano-supporters on cellobiase after immobilization

Covalent Immobilization of β-Glucosidase into Mesoporous Silica Nanoparticles from Anhydrous Acetone Enhances Its Catalytic Performance

An immobilization protocol of a model enzyme into silica nanoparticles was applied. This protocol exploited the use of the bifunctional molecule triethoxysilylpropylisocyanate (TEPI) for covalent binding through a linker of suitable length. The enzyme β-glucosidase (BG) was anchored onto wrinkled silica nanoparticles (WSNs). BG represents a bottleneck in the conversion of lignocellulosic biomass into biofuels through cellulose hydrolysis and fermentation. The key aspect of the procedure was the use of an organic solvent (anhydrous acetone) in which the enzyme was not soluble. This aimed to restrict its conformational changes and thus preserve its native structure. This approach led to a biocatalyst with improved thermal stability, characterized by high immobilization efficiency and yield. It was found that the apparent KM value was about half of that of the free enzyme. The Vmax was about the same than that of the free enzyme. The biocatalyst showed a high operational stability, losing only 30% of its activity after seven reuses.

β-Glucosidase from tartary buckwheat immobilization on bifunctionalized nano-magnetic iron oxide and its application in tea soup for aroma and flavonoid aglycone enhancement

β-Glucosidase (BG) was immobilized on the surface of bifunctionalized nano-magnetic iron oxide with silica and amine groups (Fe₃O₄@SiO₂-NH₂). The aroma and flavonoid aglycone enhancement effect of BG in tea soup was investigated. The immobilized BG-synthesized nanocomposite morphology and structure were characterized by using different analytical techniques, including Fourier transform infrared spectroscopy and scanning electron microscopy. The immobilized BG showed enhanced pH and temperature endurance at an optimum pH of 5.0 and temperature of 65 °C. After seven cycles of reuse, immobilized BG showed 51.8% initial activity. Immobilized-BG treatment in green tea and black tea soup elevated the aroma content by approximately 16% and 48%, respectively. In addition, flavonoid aglycones, such as myricetin, kaempferol, and quercetin, in green tea and black tea soup increased by approximately 65- and 5-fold, respectively. These results suggested that immobilized BG showed excellent potential in the enhancement of aroma and effectively hydrolyzed the flavonoid glycosides to release flavonoid aglycones in tea soup. Hence, this study provides a green and sustainable approach for the tea industry to efficiently enhance tea soup properties.

The effect of pore morphology on the catalytic performance of β-glucosidase immobilized into mesoporous silica

β-Glucosidase (BG) was immobilized by adsorption on wrinkled silica nanoparticles (WSNs) and on tannic acid-templated mesoporous silica nanoparticles (TA-MSNPs). The effect induced by a different morphology of the pores of the sorbent on the catalytic performance of β-glucosidase was investigated. A complete textural and morphological characterization of the two samples was performed by Brunauer–Emmett–Teller (BET) method, Fourier Transform Infrared (FT-IR) and transmission electron microscopy (TEM). The results demonstrated that the catalytic performance of the immobilized enzyme depends on the pores size of sorbent but a key factor is the pores morphology. In fact, the BG immobilized on WSNs and TA-MSNPs (BG/WSNs and BG/TA-MSNPs) shows in both cases good catalytic performances in cellobiose hydrolysis, but the catalyst with the best performance is BG/WSNs, in which the support exhibits a central-radial pore structure and a hierarchical trimodal micro-mesoporous pore size. This peculiar morphology allows the enzyme to settle in a place where the interactions with the walls are maximized, increasing its conformational rigidity. Furthermore, the enzyme is prevalently collocated in the interior of pore so that the pores are not completely capped.

Immobilization of β-glucosidase onto silicon oxide nanoparticles and augment of phenolics in sugarcane juice

Purified β-glucosidase was immobilized on SiO2 nanoparticles with 52 % efficiency and 14.1 % yield. It had a temperature optima at 60 °C and pH optima of 5.0. Immobilized enzyme was fairly stable at 60-70 °C. After immobilization, the Km value of β-glucosidase for p-nitrophenyl-β-d-glucopyranoside (pNPG) increased from 0.9 to 1.074 mM and Vmax decreased from 3.5 to 1.513 U/mg. The immobilized enzyme showed improved storage stability at temperature 4 and 25 °C and was reusable for up to ten cycles with 70 % residual activity in pNPG and 60 % residual activity in sugarcane juice treatment. Sugarcane juice density, viscosity; surface tension etc. changed after treatment with immobilized β-glucosidase. β-Glucosidase treated sugarcane juice showed higher phenolics than untreated sugarcane juice. Caffeic acid which was absent in juice, was detected in β-glucosidase treated juice at a concentration of about 1 mg/L.

Application of ZnO Nanoparticles for Improving the Thermal and pH Stability of Crude Cellulase Obtained from Aspergillus fumigatus AA001

Cellulases are the enzymes which are responsible for the hydrolysis of cellulosic biomass. In this study thermal and pH stability of crude cellulase has been investigated in the presence of zinc oxide (ZnO) nanoparticles. We synthesized ZnO nanoparticle by sol-gel method and characterized through various techniques including, X-ray Diffraction, ultraviolet-visible spectroscope, field emission scanning electron microscope and high resolution scanning electron microscope. The crude thermostable cellulase has been obtained from the Aspergillus fumigatus AA001 and treated with ZnO nanoparticle which shows thermal stability at 65°C up to 10 h whereas it showed pH stability in the alkaline pH range and retained its 53% of relative activity at pH 10.5. These findings may be promising in the area of biofuels production.

Enhanced saccharification of sugarcane bagasse using soluble cellulase supplemented with immobilized β-glucosidase

The β-glucosidase (BG) enzyme plays a vital role in the hydrolysis of lignocellulosic biomass. Supplementation of the hydrolysis reaction medium with BG can reduce inhibitory effects, leading to greater conversion. In addition, the inclusion of immobilized BG can be a useful way of increasing enzyme stability and recyclability. BG was adsorbed on polyacrylic resin activated by carboxyl groups (BG-PC) and covalently attached to glyoxyl-agarose (BG-GA). BG-PC exhibited similar behavior to soluble BG in the hydrolysis of cellobiose, while BG-GA hydrolyzed the same substrate at a lower rate. However, the thermal stability of BG-GA was higher than that of free BG. Hydrolysis of pretreated sugarcane bagasse catalyzed by soluble cellulase supplemented with immobilized BG improved the conversion by up to 40% after 96 h of reaction. Both derivatives remained stable up to the third cycle and losses of activity were less than 50% after five cycles.

Immobilization of L-arabinitol dehydrogenase on aldehyde-functionalized silicon oxide nanoparticles for L-xylulose production

L-Xylulose is a potential starting material for therapeutics. However, its translation into clinical practice has been hampered by its inherently low bioavailability. In addition, the high cost associated with the production of L-xylulose is a major factor hindering its rapid deployment beyond the laboratory. In the current study, L-arabinitol 4-dehydrogenase from Hypocrea jecorina (HjLAD), which catalyzes the conversion of L-arabinitol into L-xylulose, was immobilized onto various carriers, and the immobilized enzymes were characterized. HjLAD covalently immobilized onto silicon oxide nanoparticles showed the highest immobilization efficiency (94.7 %). This report presents a comparative characterization of free and immobilized HjLAD, including its thermostability and kinetic parameters. The thermostability of HjLAD immobilized on silicon oxide nanoparticles was more than 14.2-fold higher than free HjLAD; the t1/2 of HjLAD at 25 °C was enhanced from 190 min (free) to 45 h (immobilized). In addition, the immobilized HjLAD retained 94 % of its initial activity after 10 cycles. When the immobilized HjLAD was used to catalyze the biotransformation of L-arabinitol to L-xylulose, 66 % conversion and a productivity of 7.9 g · h(-1) · L(-1) were achieved. The enhanced thermostability and reusability of HjLAD suggest that immobilization of HjLAD onto silicon oxide nanoparticles has the potential for use in the industrial production of rare sugars.

Immobilization of β-glucosidase on a magnetic nanoparticle improves thermostability: application in cellobiose hydrolysis

The objective of the present work was to develop a thermostable β-glucosidase through immobilization on a nanoscale carrier for potential application in biofuel production. β-Glucosidase (BGL) from Aspergillus niger was immobilized to functionalized magnetic nanoparticles by covalent binding. Immobilized nanoparticles showed 93% immobilization binding. Immobilized and free BGL were characterized using Transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR) techniques. Free and immobilized enzyme exhibited different pH-optima at pH 4.0 and 6.0, respectively, but had the same temperature optima at 60 °C. Michaelis constant (KM) was 3.5 and 4.3mM for free and immobilized BGL. Thermal stability of the immobilized enzyme was enhanced at 70 °C. The immobilized nanoparticle-enzyme conjugate retained more than 50% enzyme activity up to the 16th cycle. Maximum glucose synthesis from cellobiose hydrolysis by immobilized BGL was achieved at 16 h.

From protein engineering to immobilization: promising strategies for the upgrade of industrial enzymes

Enzymes found in nature have been exploited in industry due to their inherent catalytic properties in complex chemical processes under mild experimental and environmental conditions. The desired industrial goal is often difficult to achieve using the native form of the enzyme. Recent developments in protein engineering have revolutionized the development of commercially available enzymes into better industrial catalysts. Protein engineering aims at modifying the sequence of a protein, and hence its structure, to create enzymes with improved functional properties such as stability, specific activity, inhibition by reaction products, and selectivity towards non-natural substrates. Soluble enzymes are often immobilized onto solid insoluble supports to be reused in continuous processes and to facilitate the economical recovery of the enzyme after the reaction without any significant loss to its biochemical properties. Immobilization confers considerable stability towards temperature variations and organic solvents. Multipoint and multisubunit covalent attachments of enzymes on appropriately functionalized supports via linkers provide rigidity to the immobilized enzyme structure, ultimately resulting in improved enzyme stability. Protein engineering and immobilization techniques are sequential and compatible approaches for the improvement of enzyme properties. The present review highlights and summarizes various studies that have aimed to improve the biochemical properties of industrially significant enzymes.

Amino-Functionalized Silica Nanoparticles: In Vitro Evaluation for Targeted Delivery and Therapy of Pancreatic Cancer

We report a method of synthesis and optimization of amino-functionalized silica nanoparticles (SiNPs) and their in vitro evaluation as targeted delivery vehicles for the potential treatment of pancreatic cancer. SiNPs can efficiently encapsulate doxorubicin and can be attached to a targeting moiety such as anti-Claudin-4 (CLN4). The preferential uptake in pancreatic cancer cells, where CLN4 is overexpressed, of SiNPs when conjugated to CLN4 antibody (compared to nonconjugated SiNPs) was confirmed by confocal microscopy. SiNPs encapsulating doxorubicin had greater efficacy in MTT assays than free doxorubicin, and when conjugated to CLN4, the efficacy was dramatically increased (at 1 μM). No apparent carrier toxicity was observed when void SiNPs were used. SiNPs carrying a chemotherapeutic drug have the potential to be used as a targeted therapy for lethal cancers, such as pancreatic cancer. Also, incorporation of fluorescent probes in these SiNPs creates the possibility of their use as an imaging probe for diagnostic purposes.