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  • Enzyme selectivity of many enzymes like galactosidases

    2019-11-29

    Enzyme selectivity of many SQ 22536 like β-galactosidases, acylases, epoxyhydrolases, lipases, etc. has also been modulated by using different immobilization techniques. It can result in the selection of optimal biocatalyst for different processes. This has many advantages over strategies like genetic and protein engineering, for example the ease of the process, high enantio-selectivity, reusability and advantage of using the enzyme for a variety of reactions in aqueous and non-aqueous environments [101]. Enzymes attached to a single nanoparticle with medium exposed active sites showed cooperative catalysis of the substrate and increased enzyme activity. However, at higher enzyme concentration agglomeration takes place and the active site is not accessible to the substrate, which lowers the enzyme catalytic activity even when enzyme is retaining its native structure. The agglomeration starts with the van der Waals or electrostatic interactions between the enzyme and nanoparticles. Changes in the conformation of enzyme may also lead to agglomeration. Finally, by maintaining a proper ratio between the enzyme and citrate stabilized gold nanoparticles gives a new path for modulating catalytic activity of the enzyme. This approach can be further used for modulating the activity of other biomolecules, enzymes, manufactured nanomaterial in environmental systems, and human health [102].
    Merits and demerits of enzyme immobilization The enzyme immobilization by simple adsorption prevents chemical modifications of the enzyme and this process is simpler and cheaper as compared to other methods. However, enzymes immobilized through chemical linkages have higher binding strength and better enzyme stability that causes minimization of enzyme leakage. The immobilization process usually improves thermal, pH and storage stabilities, and enables the enzyme to work in a broader range of pH and temperature [103].
    Applications, examined properties and factors affecting enzyme immobilization Immobilization changes the catalytic properties of the enzyme, such as improved operational, thermal, chemical, pH, storage and temperature stability, reusability, and enhanced adsorption efficiency [104]. While using suitable carrier and carrier modifier for enzyme immobilization, certain properties are frequently examined, such as effect of pore size in case of mesoporous silica, optimization of glutaraldehyde concentration while modifying surface amino groups, amount of modifying agent or carrier versus enzyme adsorbed, influence of inhibitory agents and organic solvents, effect of ionic liquid, immobilization method, reusability versus catalytic activity and effect of water content on the structure of carrier [75]. The major applications of enzyme immobilization include sequestration and hydration of carbon dioxide by bovine carbonic anhydrase immobilized on mesoporous silica (SBA-15) using 3-aminopropyltriethoxysilane as carrier modifier [112]. Biomolecule separation and bioadsorption by using carboxymethylcellulase from Trichoderma reesei immobilized on large pore silica (FDU-12) and 3-mercaptopropyl-, phenyl and vinyltrimethoxysilanes, 3-aminopropyltriethoxysilane as carrier modifier [126]. Hydrolysis of cellulose to glucose in aqueous medium is achieved by using cellulase from Trichoderma reesei immobilized on mesoporous silica [127]. Digestion of proteins by using chymotrypsin adsorbed on aptamer-silica beads and glutaraldehyde as carrier modifier [128]. Yeast alcohol dehydrogenase (YADH) immobilized on polyaniline coated silver nanoparticles showed a slight increase in optimum temperature and enhanced pH, temperature and storage stabilities [129]. Similar catalytic variations were obtained when YADH was immobilized on electrically conductive polypyrrole-titanium(IV)phosphate nanocomposite [130]. Tannic acid stabilized silver nanoparticles serves as a selective tool for the detection of melamine [131]. Electrode sensor for glucose detection by using glucose oxidase adsorbed on mesoporous silica (vesicle like and rod like) and 3-aminopropyltriethoxysilane as carrier modifier [11]. Esterification of linoleic acid in organic medium by lipase from Candida rugosa immobilized on mesoporous silica (MSU-H) using glutaraldehyde as carrier modifier [132]. Hydrolytic degradation of cellulose by β-glucosidase, endo-glucanase and exo-glucanase adsorbed on gold-doped magnetic silica nanoparticles and gold nanoparticles using 3-mercaptopropyltriethoxysilane as carrier modifier [117], enzymatic biosensor for glucose detection by glucose oxidase from Aspergillus niger immobilized on gold nanotubes using glutaraldehyde as carrier modifier [118]. Biosensor for H2O2 detection by horseradish peroxidase adsorbed on titanium sol-gel film [132]. Synthesis of isomaltose using dextransucrase by endodextranase immobilized on silica, streamline DEAE, bentonite and hydroxyapatite [77]. Transesterification by lipase using chitosan beads as carrier [120]. Production of diacylglycerols from glycerolysis of soybean oil by lacitase ultra immobilized on macroporous resin [133]. Protein digestion by trypsin immobilized on nylon membranes using poly(styrene sulfonate) as carrier modifier [123]. Some important immobilized enzymes and modified nanoparticle combinations used to obtain desirable catalytic properties are discussed in (Table 1).