A review on the immobilization of pepsin: A Lys-poor enzyme that is unstable at alkaline pH values

Changes in ficin specificity by different substrate proteins promoted by enzyme immobilization

Ficin extract has been immobilized using different supports: glyoxyl and Aspartic/1,6 hexamethylenediamine (Asp/HA) agarose beads. The latter was later submitted to glutaraldehyde modification to get covalent immobilization. The activities of these 3 kinds of biocatalysts were compared utilizing 4 different substrates, casein, hemoglobin and bovine serum albumin and benzoyl-arginine-p-nitroanilide at pH 7 and 5. Using glyoxyl-agarose, the effect of enzyme-support reaction time on the activity versus the four substrates at both pH values was studied. Reaction time has been shown to distort the enzyme due to an increase in the number of covalent support-enzyme bonds. Surprisingly, for all the substrates and conditions the prolongation of the enzyme-support reaction did not imply a decrease in enzyme activity. Using the Asp/HA supports (with different amount of HA) differences in the effect on enzyme activity versus the different substrates are much more significant, while with some substrates the immobilization produced a decrease in enzyme activity, with in other cases the activity increased. These different effects are even increased after glutaraldehyde treatment. That way, the conformational changes induced by the biocatalyst immobilization or the chemical modification fully altered the enzyme protein specificity. This may also have some implications when following enzyme inactivation.

Hydrolysis of Casein by Pepsin Immobilized on Heterofunctional Supports to Produce Antioxidant Peptides

A study was carried out on the immobilization of pepsin in activated carbon functionalized by different techniques (glutaraldehyde, genipin, and metallization) aiming at its application in obtaining bioactive peptides through casein hydrolysis. Studies of the immobilized derivatives were carried out in addition to the evaluation of the antioxidant potential of the peptides. Among the pH range studied, pH 3.0 was selected due to the higher activity of the derivatives at this pH. The support modification by metallization was the method with the best results, providing a 121% increase in enzymatic activity compared to other immobilization methods. In addition, this derivative provided activity closer to the soluble enzyme activity (3.30 U) and better storage stability, and allows reuse for more than 8 cycles. In turn, the peptides from casein hydrolysis showed potential as antioxidant agents, with a DPPH radical scavenging activity higher than 70%, maximum protection against β-carotene oxidation close to 70%, and a maximum reducing power of Fe(III) into Fe(II) of 400 uM by the FRAP assay. The results showed that the new techniques for modification of activated carbon can be a promising approach for pepsin immobilization.

Development of an Automated, Ultra-Rapid Bottom-Up Proteomics Workflow Utilizing Alginate-Based Hydrogels

A new approach to sample preparation and enzymatic digestion in bottom-up proteomics has been developed using alginate-based hydrogel entrapment of enzymes. This hydrogel facilitates rapid and room-temperature digestions with multienzyme capabilities. Three methodologies were tested: within microcentrifuge tubes, in situ pipette tips, and automated robotic liquid handling. Factorial experimental design identified a 1 h, room temperature, pepsin-trypsin dual-enzyme digestion as optimal for sequence coverage and protein group identification, comparable to a gold-standard overnight proteomic protocol. This method promises significant advancements in proteomic analysis by enhancing reusability, speed, throughput, convenience, and cost-effectiveness, without hindering digestion efficiency.

Tailoring the specificity of ficin versus large hemoglobin and small casein by co-immobilizing inert proteins on the immobilized enzyme layer and further modification with aldehyde dextran

Ficin has been immobilized at full loading on glyoxyl agarose beads. Then, ficin was blocked with 2,2'-dipyridyldisulfide. To be effective, the modification must be performed in the presence of 0.5 M urea, as the enzyme was not inhibited under standard conditions, very likely because the catalytic Cys was not fully exposed to the medium. Activity could be fully recovered by incubation with 1 M mercaptoethanol. This biocatalyst could hydrolyze hemoglobin and casein. The objective of this paper was to increase the enzyme specificity versus small proteins by generating steric hindrances to the access of large proteins. The step by step blocking via ionic exchange of the biocatalyst with aminated bovine serum albumin (BSA), aldehyde dextran and a second layer of aminated BSA produced a biocatalyst that maintained its activity versus small synthetic substrates, increased the biocatalyst stability, while reduced its activity to over 50 % versus casein. Interestingly, this treatment almost fully annulled the activity versus hemoglobin, more effectively at 37 °C than at 55 °C. The biocatalyst could be reused 5 times without changes in activity. The changes could be caused by steric hindrances, but it cannot be discarded some changes in enzyme sequence specificity caused by the modifications.

Microfluidic programmable strategies for channels and flow

This review summarizes programmable microfluidics, an advanced method for precise fluid control in microfluidic technology through microchannel design or liquid properties, referring to microvalves, micropumps, digital microfluidics, multiplexers, micromixers, slip-, and block-based configurations. Different microvalve types, including electrokinetic, hydraulic/pneumatic, pinch, phase-change and check valves, cater to diverse experimental needs. Programmable micropumps, such as passive and active micropumps, play a crucial role in achieving precise fluid control and automation. Due to their small size and high integration, microvalves and micropumps are widely used in medical devices and biological analysis. In addition, this review provides an in-depth exploration of the applications of digital microfluidics, multiplexed microfluidics, and mixer-based microfluidics in the manipulation of liquid movement, mixing, and splitting. These methodologies leverage the physical properties of liquids, such as capillary forces and dielectric forces, to achieve precise control over fluid dynamics. SlipChip technology, which branches into rotational SlipChip and translational SlipChip, controls fluid through sliding motion of the microchannel. On the other hand, innovative designs in microfluidic systems pursue better modularity, reconfigurability and ease of assembly. Different assembly strategies, from one-dimensional assembly blocks and two-dimensional Lego®-style blocks to three-dimensional reconfigurable modules, aim to enhance flexibility and accessibility. These technologies enhance user-friendliness and accessibility by offering integrated control systems, making them potentially usable outside of specialized technical labs. Microfluidic programmable strategies for channels and flow hold promising applications in biomedical research, chemical analysis and drug screening, providing theoretical and practical guidance for broader utilization in scientific research and practical applications.

Efficient and easible biocatalysts: Strategies for enzyme improvement. A review

Owing to the environmental friendliness and vast advantages that enzymes offer in the biotechnology and industry fields, biocatalysts are a prolific investigation field. However, the low catalytic activity, stability, and specific selectivity of the enzyme limit the range of the reaction enzymes involved in. A comprehensive understanding of the protein structure and dynamics in terms of molecular details enables us to tackle these limitations effectively and enhance the catalytic activity by enzyme engineering or modifying the supports and solvents. Along with different strategies including computational, enzyme engineering based on DNA recombination, enzyme immobilization, additives, chemical modification, and physicochemical modification approaches can be promising for the wide spread of industrial enzyme usage. This is attributed to the successful application of biocatalysts in industrial and synthetic processes requires a system that exhibits stability, activity, and reusability in a continuous flow process, thereby reducing the production cost. The main goal of this review is to display relevant approaches for improving enzyme characteristics to overcome their industrial application.

Laccase Immobilized on Arginine-Functionalized Boron Nitride Nanosheets for Enhanced Atrazine Degradation

Enzyme-mediated systems have been widely employed for the biotransformation of environmental contaminants. However, the catalytic performance of free enzymes is restricted by the rapid loss of their catalytic activity, stability, and reusability. In this work, we developed an enzyme immobilization platform by elaborately anchoring fungal laccase onto arginine-functionalized boron nitride nanosheets (BNNS-Arg@Lac). BNNS-Arg@Lac showcased ∼75% immobilization yield and enhanced stability against fluctuating pH values and temperatures, along with remarkable reusability across six consecutive cycles, outperforming free natural laccase (nlaccase). A model pollutant, atrazine, was selected for a proof-of-concept demonstration, given the substantial environmental and public health concerns in agriculture runoff. BNNS-Arg@Lac-catalyzed atrazine degradation rate was nearly twice that of nlaccase. Moreover, BNNS-Arg@Lac consistently demonstrated superior atrazine degradation in synthetic agricultural wastewater and various mediator systems compared to nlaccase. Comprehensive product analysis unraveled distinct degradation pathways for BNNS-Arg@Lac and nlaccase. Overall, this research provides a foundation for the future development of enzyme-nanomaterial hybrids for degrading environmental chemicals and may unlock new potential for green and efficient resource recovery and waste management strategies.

Support Enzyme Loading Influences the Effect of Aldehyde Dextran Modification on the Specificity of Immobilized Ficin for Large Proteins

It has been reported that the modification of immobilized glyoxyl-ficin with aldehyde dextran can promote steric hindrances that greatly reduce the activity of the immobilized protease against hemoglobin, while the protease still maintained a reasonable level of activity against casein. In this paper, we studied if this effect may be different depending on the amount of ficin loaded on the support. For this purpose, both the moderately loaded and the overloaded glyoxyl-ficin biocatalysts were prepared and modified with aldehyde dextran. While the moderately loaded biocatalyst had a significantly reduced activity, mainly against hemoglobin, the activity of the overloaded biocatalyst was almost maintained. This suggests that aldehyde dextran was able to modify areas of the moderately loaded enzyme that were not available when the enzyme was overloaded. This modification promoted a significant increase in biocatalyst stability for both biocatalysts, but the stability was higher for the overloaded biocatalyst (perhaps due to a combination of inter- and intramolecular crosslinking).

Development of automated proteomic workflows utilizing silicon-based coupling agents

Automated methods for enzyme immobilization via 4-triethoxysilylbutyraldehyde (TESB) derived silicone-based coupling agents were developed. TESB and its oxidized derivative, 4-triethoxysilylbutanoic acid (TESBA), were determined to be the most effective. The resulting immobilized enzyme particles (IEPs) displayed robustness, rapid digestion, and immobilization efficiency of 51 ± 8%. Furthermore, we automated the IEP procedure, allowing for multiple enzymes, and/or coupling agents to be fabricated at once, in a fraction of the time via an Agilent Bravo. The automated trypsin TESB and TESBA IEPs were shown to rival a classical in-gel digestion method. Moreover, pepsin IEPs favored cleavage at leucine (>50%) over aromatic and methionine residues. The IEP method was then adapted for an in-situ immobilized enzyme microreactor (IMER) fabrication. We determined that TESBA could functionalize the silica capillary's inner wall while simultaneously acting as an enzyme coupler. The IMER digestion of bovine serum albumin (BSA), mirroring IEP digestion conditions, yielded a 33-40% primary sequence coverage per LC-MS/MS analysis in as little as 15 min. Overall, our findings underscore the potential of both IEP and IMER methods, paving the way for automated analysis and a reduction in enzyme waste through reuse, thereby contributing to a more cost-effective and timely study of the proteome. SIGNIFICANCE: This research introduces 4-triethoxysilylbutyraldehyde (TESB) and its derivatives as silicon-based enzyme coupling agents and an automated liquid handling method for bottom-up proteomics (BUP) while streamlining sample preparation for high-throughput processing. Additionally, immobilized enzyme particle (IEP) fabrication and digestion within the 96-well plate allows for flexibility in protocol where different enzyme-coupler combinations can be employed simultaneously. By enabling the digestion of entire microplates and reducing manual labor, the proposed method enhances reproducibility and offers a more efficient alternative to classical in-gel techniques. Furthermore, pepsin IEPs were noted to favor cleavage at leucine residues which represents an interesting finding when compared to the literature that warrants further study. The capability of immobilized enzyme microreactors (IMER) for rapid digestion (in as little as 15 min) demonstrated the system's efficiency and potential for rapid proteomic analysis. This advancement in BUP not only improves efficiency, but also opens avenues for a fully automated, mass spectrometry-integrated proteomics workflow, promising to expedite research and discoveries in complex biological studies.

A review on the immobilization of bromelain

This review shows the endeavors performed to prepare immobilized formulations of bromelain extract, usually from pineapple, and their use in diverse applications. This extract has a potent proteolytic component that is based on thiol proteases, which differ depending on the location on the fruit. Stem and fruit are the areas where higher activity is found. The edible origin of this enzyme is one of the features that determines the applications of the immobilized bromelain to a more significant degree. The enzyme has been immobilized on a wide diversity of supports via different strategies (covalent bonds, ion exchange), and also forming ex novo solids (nanoflowers, CLEAs, trapping in alginate beads, etc.). The use of preexisting nanoparticles as immobilization supports is relevant, as this facilitates one of the main applications of the immobilized enzyme, in therapeutic applications (as wound dressing and healing components, antibacterial or anticancer, mucus mobility control, etc.). A curiosity is the immobilization of this enzyme on spores of probiotic microorganisms via adsorption, in order to have a perfect in vivo compatibility. Other outstanding applications of the immobilized enzyme are in the stabilization of wine versus haze during storage, mainly when immobilized on chitosan. Curiously, the immobilized bromelain has been scarcely applied in the production of bioactive peptides.

Pepsin immobilization on activated carbon and functionalized with glutaraldehyde and genipin for the synthesis of antioxidant peptides of goat casein

In this article, the synthesis of antioxidant peptides in the enzymatic hydrolysis of caprine casein was analyzed at three different time points (60 min, 90 min, and 120 min) using immobilized pepsin on activated and modified carbon (AC, ACF, ACG 50, ACG 100). The immobilization assays revealed a reduction in the biocatalysts' activity compared to the free enzyme. Among the modified ones, ACG 50 exhibited greater activity and better efficiency for reuse cycles, with superior values after 60 min and 90 min. Peptide synthesis was observed under all studied conditions. Analyses (DPPH, β-carotene/linoleic acid, FRAP) confirmed the antioxidant potential of the peptides generated by the immobilized enzyme. However, the immobilized enzyme in ACG 50 and ACG 100, combined with longer hydrolysis times, allowed the formation of peptides with an antioxidant capacity greater than or equivalent to those generated by the free enzyme, despite reduced enzymatic activity.

Proteases: Importance, Immobilization Protocols, Potential of Activated Carbon as Support, and the Importance of Modifying Supports for Immobilization

Although enzymes have been used for thousands of years, their application in industrial processes has gained importance since the 20th century due to technological and scientific advances in several areas, including biochemistry [...].

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.

Harnessing the Potential of Chitosan and Its Derivatives for Enhanced Functionalities in Food Applications

As one of the most abundant natural polysaccharides that possess good biological activity, chitosan is extracted from chitin. Its application in the food field is being increasingly valued. However, chitosan extraction is difficult, and its poor solubility limits its application. At present, the extraction methods include the acid-base method, new chemical methods, and biological methods. The extraction rates of chitin/chitosan are 4-55%, 13-14%, and 15-28%, respectively. Different chemical modifications have different effects on chitosan, making it applicable in different fields. This article reviews and compares the extraction and chemical modification methods of chitosan, emphasizing the importance of green extraction methods. Finally, the application prospects of chitosan in the food industry are discussed. This will promote the understanding of the advantages and disadvantages of different extraction methods for chitosan as well as the relationship between modification and application, providing valuable insights for the future development of chitosan.

Construction and Application of a Pepsin-Functionalized Covalent Organic Framework with Prominent Chiral Recognition Ability

The stable Pepsin@covalent organic framework (Pepsin@COF) were constructed base on matching COF pore diameter to pepsin dimension. It exhibits excellent chiral recognition capabilities (e. e. % up to 62.63 %) and potential for enantioseparation. Furthermore, a positive correlation between the immobilized enzyme activity and chiral recognition was revealed, offering insights for the design of biocatalytic nanosystems in chiral separation.

Proteases immobilized on nanomaterials for biocatalytic, environmental and biomedical applications: Advantages and drawbacks

Proteases have gained significant scientific and industrial interest due to their unique biocatalytic characteristics and broad-spectrum applications in different industries. The development of robust nanobiocatalytic systems by attaching proteases onto various nanostructured materials as fascinating and novel nanocarriers has demonstrated exceptional biocatalytic performance, substantial stability, and ease of recyclability over multiple reaction cycles under different chemical and physical conditions. Proteases immobilized on nanocarriers may be much more resistant to denaturation caused by extreme temperatures or pH values, detergents, organic solvents, and other protein denaturants than free enzymes. Immobilized proteases may present a lower inhibition. The use of non-porous materials in the immobilization prevents diffusion and steric hindrances during the binding of the substrate to the active sites of enzymes compared to immobilization onto porous materials; when using very large or solid substrates, orientation of the enzyme must always be adequate. The advantages and problems of the immobilization of proteases on nanoparticles are discussed in this review. The continuous and batch reactor operations of nanocarrier-immobilized proteases have been successfully investigated for a variety of applications in the leather, detergent, biomedical, food, and pharmaceutical industries. Information about immobilized proteases on various nanocarriers and nanomaterials has been systematically compiled here. Furthermore, different industrial applications of immobilized proteases have also been highlighted in this review.

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.

A critical review of enzymes immobilized on chitosan composites: characterization and applications

Enzymes with industrial significance are typically used in biological processes. However, instability, high sensitivity, and impractical recovery are the major drawbacks of enzymes in practical applications. In recent years, the immobilization technology has attracted wide attention to overcoming these restrictions and improving the efficiency of enzyme applications. Chitosan (CS) is a unique functional substance with biocompatibility, biodegradability, non-toxicity, and antibacterial properties. Chitosan composites are anticipated to be widely used in the near future for a variety of purposes, including as supports for enzyme immobilization, because of their advantages. Therefor this review explores the effects of the chitosan's structure, molecular weight, degree of deacetylation on the enzyme immobilized, effect of key factors, and the enzymes immobilized on chitosan based composites for numerous applications, including the fields of biosensor, biomedical science, food industry, environmental protection, and industrial production. Moreover, this study carefully investigates the advantages and disadvantages of using these composites as well as their potential in the future.

Microplastics exhibit lower carrying effects on the bioaccessibility and cytotoxicity of lead than montmorillonite clay particles

Microplastics (MPs) in the environment are always colonized by microbes, which may have implications for carrying effect of pollutants and exposure risk in organisms. We present the crucial impacts and mechanisms of microbial colonization on the bioaccessibility and toxicity of Pb(II) loaded in disposable box-derived polypropylene (PP) and polystyrene (PS) MPs and montmorillonite (MMT) clay particles. After 45 d incubation, higher biomass measured by crystal violet staining were detected in MMT (1.23) than in PP and PS (0.400 and 0.721) indicating preferential colonization of microbes in clay particles. Microbial colonization further enhanced the sorption ability toward Pb(II), but inhibited the desorption and bioaccessibility of enriched Pb(II) in zebrafish and decreased the toxicity to gastric epithelial cells in an order of MMT > PS ≈ PP. The crucial effects were mainly because microbe-colonized substrates possessed higher oxygen functional groups and specific surface area and exhibited stronger interactions with Pb(II) and digestive component (i.e., pepsin) than pure substrates. This decreased the available soluble pepsin for complexing with sorbed Pb(II). The findings highlight the role of microbial colonization in modulating the exposure risks of artificial and natural substrate-associated pollutants and suggest that the risks of MPs may be overestimated compared to clay particles.

Genipin crosslinked porous chitosan beads as robust supports for β-galactosidase immobilization: Characterization, stability, and bioprocessing potential

This study aimed to modify the porosity of chitosan beads using Na2CO3 as a porogen agent and to crosslink them with genipin for the immobilization of β-galactosidase from Aspergillus oryzae. Immobilization was performed under four different pH conditions (4.5, 6.0, 7.5, and 9.0), resulting in biocatalysts named B4, B6, B7, and B9, respectively. The immobilized enzymes were characterized for immobilization parameters and stability, including thermal, pH, storage, and operational stability. The optimal conditions for the support were determined as 50 mM Na2CO3. The biocatalyst exhibited nearly 100 % retention of initial activity after 5 h of incubation at different pH conditions and showed improved thermal stability compared to the free enzyme across all pH conditions. After 50 cycles of lactose hydrolysis, all biocatalysts retained at least 71 % of their initial activity, with B6 retaining nearly 100 %. Scanning electron microscopy revealed structural modifications, particularly in B4, leading to weakened support structure after reuse. Continuous lactose hydrolysis showed increased productivity from 41.3 to 48.1 g L-1 h-1 for B6, with 78.1 % retention of initial capacity. All biocatalysts retained >95 % activity when stored at 4 °C for 20 weeks, highlighting their suitability for enzyme immobilization in continuous and discontinuous bioprocesses.

Hydrogen-Deuterium Exchange Epitope Mapping of Glycosylated Epitopes Enabled by Online Immobilized Glycosidase

Hydrogen-deuterium exchange coupled with mass spectrometry (HDX-MS) is widely used for monoclonal antibody (mAb) epitope mapping, which aids in the development of therapeutic mAbs and vaccines, as well as enables the understanding of viral immune evasion. Numerous mAbs are known to recognize N-glycosylated epitopes and to bind in close proximity to an N-glycan site; however, glycosylated protein sites are typically obscured from HDX detection as a result of the inherent heterogeneity of glycans. To overcome this limitation, we covalently immobilized the glycosidase PNGase Dj on a solid resin and incorporated it into an online HDX-MS workflow for post-HDX deglycosylation. The resin-immobilized PNGase Dj exhibited robust tolerance to various buffer conditions and was employed in a column format that can be readily adapted into a typical HDX-MS platform. Using this system, we were able to obtain full sequence coverage of the SARS-CoV-2 receptor-binding domain (RBD) and map the glycosylated epitope of the glycan-binding mAb S309 to the RBD.

(Magnetic) Cross-Linked Enzyme Aggregates of Cellulase from T. reesei: A Stable and Efficient Biocatalyst

Cross-linked enzyme aggregates (CLEAs) represent an effective tool for carrier-free immobilization of enzymes. The present study promotes a successful application of functionalized magnetic nanoparticles (MNPs) for stabilization of cellulase CLEAs. Catalytically active CLEAs and magnetic cross-linked enzyme aggregates (mCLEAs) of cellulase from Trichoderma reesei were prepared using glutaraldehyde (GA) as a cross-linking agent and the catalytic activity and stability of the CLEAs/mCLEAs were investigated. The influence of precipitation agents, cross-linker concentration, concentration of enzyme, addition of bovine serum albumin (BSA), and addition of sodium cyanoborohydride (NaBH₃CN) on expressed activity and immobilization yield of CLEAs/mCLEAs was studied. Particularly, reducing the unsaturated Schiff's base to form irreversible linkages is important and improved the activity of CLEAs (86%) and mCLEAs (91%). For increased applicability of CLEAs/mCLEAs, we enhanced the activity and stability at mild biochemical process conditions. The reusability after 10 cycles of both CLEAs and mCLEAs was investigated, which retained 72% and 65% of the initial activity, respectively. The thermal stability of CLEAs and mCLEAs in comparison with the non-immobilized enzyme was obtained at 30 °C (145.65% and 188.7%, respectively) and 50 °C (185.1% and 141.4%, respectively). Kinetic parameters were determined for CLEAs and mCLEAs, and the K_M constant was found at 0.055 ± 0.0102 mM and 0.037 ± 0.0012 mM, respectively. The maximum velocity rate (V_max) was calculated as 1.12 ± 0.0012 µmol/min for CLEA and 1.17 ± 0.0023 µmol/min for mCLEA. Structural characterization was studied using XRD, SEM, and FT-IR. Catalytical properties of immobilized enzyme were improved with the addition of reducent NaBH₃CN by enhancing the activity of CLEAs and with addition of functionalized aminosilane MNPs by enhancing the activity of mCLEAs.

Preparation of immobilized pepsin for extraction of collagen from bovine hide

In the extraction of collagens from mammalian tissues, the free pepsin used in the acid-pepsin extraction system is hard to recycle, and there is a risk of enzyme protein contamination in the extracted collagen products, which limits their applications. To solve this problem, an immobilized pepsin was successfully prepared via the covalent crosslinking of glutaraldehyde using a 3-aminopropyltriethoxysilane (APTES) surface modified silica clay as the support. The immobilized pepsin was applied for the extraction of collagen from bovine hide. The optimal immobilization process involves incubating pepsin with an initial concentration of 35 mg mL^-1 and glutaraldehyde with 5% activated APTES modified silica clay at 25 °C for 60 min, by which the loading amount of pepsin was 220 mg g^-1 and the activity of the immobilized pepsin was 4.2 U mg^-1. The collagen extracted using acetic acid and the immobilized pepsin method retained its complete triple helix structure. This research thus details an effective separation method using pepsin for extraction of collagen via an acetic acid-enzyme method, where the extracted collagen may be a candidate for use in biomaterial applications.

Lipase-Catalyzed Phospha-Michael Addition Reactions under Mild Conditions

Organophosphorus compounds are the core structure of many active natural products. The synthesis of these compounds is generally achieved by metal catalysis requiring specifically functionalized substrates or harsh conditions. Herein, we disclose the phospha-Michael addition reaction of biphenyphosphine oxide with various substituted β-nitrostyrenes or benzylidene malononitriles. This biocatalytic strategy provides a direct route for the synthesis of C-P bonds with good functional group compatibility and simple and practical operation. Under the optimal conditions (styrene (0.5 mmol), biphenyphosphine oxide (0.5 mmol), Novozym 435 (300 U), and EtOH (1 mL)), lipase leads to the formation of organophosphorus compounds in yields up to 94% at room temperature. Furthermore, we confirm the role of the catalytic triad of lipase in this phospha-Michael addition reaction. This new biocatalytic system will have broad applications in organic synthesis.

Zinc sulfide-chitosan hybrid nanoparticles as a robust surface for immobilization of Sillago sihama α-amylase

In the present study, zinc sulfide-chitosan hybrid nanoparticles synthesized by chemical deposition were used as a matrix for the immobilization of purified α-amylase extracted from Sillago sihama (Forsskal, 1775). In this regard, the size and morphological structure of zinc sulfide-chitosan hybrid nanoparticles before and after the stabilization process were evaluated using FT-IR, DLS methods, as well as SEM and TEM electron microscopy, and EDS analyses. Then, the efficiency of the immobilized enzyme was measured in terms of temperature, optimal pH, stability at the critical temperature, and pH values. Immobilization of α-amylase on zinc sulfide -chitosan hybrid nanoparticles increased the long-term stability, as well as its endurance to critical temperatures and pH values; however, the optimal temperature and pH values of the enzyme were not altered following the immobilization process. The kinetic parameters of the enzyme were also changed during immobilization. Enzyme immobilization increased the K_m, whereas decreased the catalytic efficiency (K_cat / K_m) of the immobilized enzyme compared with the free enzyme. These results are very important as, in most cases, enzyme immobilization reduces the activity and catalytic efficiency of enzymes. The nano-enzyme produced in this study, due to its high temperature, and pH stability, could be a good candidate for industrial applications, especially in the food industry.