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  • Central Bringing Excellence in Open Access

     JSM Biochemistry & Molecular Biology

    Cite this article: Husain Q (2017) Nanomaterials Immobilized Cellulolytic Enzymes and their Industrial Applications: A Literature Review. JSM Biochem Mol Biol 4(3): 1029.

    *Corresponding author

    Qayyum Husain, Department of Biochemistry, Aligarh Muslim University, Faculty of Life Sciences, Aligarh-202002, India, Tel: 919897701792; Email:

    Submitted: 28 July 2017

    Accepted: 07 August 2017

    Published: 09 August 2017

    ISSN: 2333-7109

    Copyright © 2017 Husain

    OPEN ACCESS

    Keywords • Enzymes • Cellulase • Cellobiase • β-1,4-glucosidase • Immobilization • Nanoparticles • Pullulanase • Reusability • Stabilization • Thermostability

    Review Article

    Nanomaterials Immobilized Cellulolytic Enzymes and their Industrial Applications: A Literature Review Qayyum Husain* Department of Biochemistry, Aligarh Muslim University, India

    Abstract

    The immobilization of cellulolytic enzymes via nanosupport minimizes the problem of steric hindrances between enzyme and carrier, as it has been frequently observed in case of enzymes immobilized on the surface of bulk supports. Cellulolytic enzymes immobilized on the surface of nanomaterials or entrapped inside polymeric nanospheres showed high catalytic efficiency and yield of immobilization. Nanomaterials bound cellulolytic enzymes were found significantly more stable against heat, pH, storage, operational and several other kinds of denaturants. These immobilized enzyme preparations were found less inhibitory to their inhibitors and products. Immobilized enzymes retained remarkably high activity on repeated uses and the nanocarriers bound cellulolytic enzymes have demonstrated their potential in various fields such as in clarification of juices and wines, extraction of plant oils and coffee, bioconversion of agricultural waste, improving the digestibility of animal feed ingredients. A major application at present is the biodegradation or bioconversion of cellulose to monomeric sugars. Agricultural waste rich in lignocellulosic material has been utilized in the production of large number of industrial products like ethanol, organic acids and other industrially important chemical compounds. Cellobiases immobilized on nanocarriers have also proved their potential as therapeutic agents.

    ABBREVIATIONS 3-APTES: 3-aminopropyl- triethoxysilane; CBD: Cellulose-

    Binding Domain; CDI: Carbodiimide; CS: Chitosan; CMC: Car- boxymethyl Cellulose; CLEA: Cross-Linked Enzyme Aggregates; EDC: (1-ethyl-3-(3-Dimethylaminopropyl) Carbodiimide Hy- drochloride; GA: Glutaraldehyde; NC: Nanocomposite; MNPs: Magnetic Nanoparticles; NMs: Nanomaterials; NPs: Nanoparti- cles; MS: Mesoporous Silica; MWCNTs: Multiwalled Carbon Na- notubes; PVA: Polyvinyl Alcohol; PMMA: Poly(Methyl Methacr- ylate); RSM: Response Surface Methodology

    INTRODUCTION Cellulose is one of the three main components of

    lignocelluloses. Lignocellulose forms the cell wall and structural tissue of almost all plant systems. It is most abundant regenerative agricultural raw material all over the globe and it is considered as one of most important substrate for the conversion of biomass to biofuels [1]. Cellulose is comprised of hundreds or thousands of glucose molecules and these glucose units are joined together via glucosidic linkages. The first step in the utilization of cellulose into various industrial sectors is its conversion into free glucose. This conversion is brought about by the sequential action of enzymes; these enzymes are known as cellulolytic enzymes [2,3].

    Cellulolytic enzymes are widely present in plants, insects, bacteria and fungi. Both aerobic and anaerobic bacteria are capable of producing cellulolytic enzymes as single enzyme or in the form of cellulosomes, multi-enzyme complexes which are comprised of several cellulolytic enzymes [4,5]. Since past few decades the application of cellulolytic enzymes has attracted a lot of attention due to increasing demand for hydrolyzed cellulose products in various industrial sectors. Numerous kinds of cellulose hydrolyzing enzymes are required for efficient hydrolysis of cellulose and these are mainly three types of synergistically acting enzymes [6,7]. Table 1 and Figure 1 demonstrate enzymatic hydrolysis of cellulose into glucose using various types of cellulolytic enzymes. Endoglucanases hydrolyze glycosidic bonds in the amorphous part of the substrate and produce water soluble oligo and polysaccharides. Cellobiohydrolases cleave crystalline ends of cellulose producing cellobiose and tetrasaccharides. Cellobiase is also known as β-glucosidase which is responsible for the hydrolysis of cellobiose into glucose monomers [8,9].

    These enzymes are employed in a large number of industrial processes, such as in cotton and paper manufacturing, food and fuel industry, extraction and clarification of fruits juices, brewery and wine, animal feed additives, detergents, agriculture and research [10,11]. Moreover, cellulolytic enzymes are gaining

  • Central Bringing Excellence in Open Access

    Husain (2017) Email:

    JSM Biochem Mol Biol 4(3): 1029 (2017) 2/16

    more and more interest for agriculture, biotechnology and bioenergy uses, especially in the utilization of cellulosic biomass for the production of renewable liquid biofuels like ethanol, butanol or other fermentative products of sugar [4,12]. The use of cellulolytic enzymes during bio-ethanol production from biomass has led to the development of an environmental friendly and sustainable technology. The development of bio-refinery is getting attention because already existing petro-refinery will be

    exhausted in near future. With such uses, these have the potential to become the largest group of industrially-used enzymes worldwide [13,14].

    Indeed, the demand for these enzymes is more rapidly growing than ever before, that has focused to the research on stable and reusable cellulolytic enzymes. With the opening of new avenues in biotechnology, the application of cellulolytic enzymes has increased into several other fields such as environmental

    Table 1: Summarizes various types of cellulolytic enzymes, their systematic names, EC number, substrates and products.

    Name of enzyme Systematic name EC number Substrates Product

    Cellulases or Endocellulases 1,4-β-D-glucan-4-glucano-hydrolase EC 3.2.1.4 Amorphous cellulose Microcyrstalline cellulose, oligo- &

    soluble polysaccharides Exocellulases or

    cellobiohydrolases 1,4-β-D-glucan cellobio-

    hydrolase EC 3.2.1.91 β-glucans.

    Microcrystalline Tetrasaccharide/disaccharides or

    cellobiose

    Cellobiases or β-glucosidases 1,4-β-D-glucoside-gluco-hydrolasease EC 3.2.1.21 Cellobiose Glucose

    Figure 1 Demonstrates enzymatic hydrolysis of cellulose into glucose.

  • Central Bringing Excellence in Open Access

    Husain (2017) Email:

    JSM Biochem Mol Biol 4(3): 1029 (2017) 3/16

    and analytical chemistry [15,16]. In order to produce soluble sugars from cellulose, cellulolytic enzymes from varying sources such as microbial, plant, insects and recombinant organism have extensively been obtained. The use of cellulolytic enzymes in cellulose based industries has been prevalent since last several decades but the use of soluble enzymes, limits their applications due to certain inherent problems such as high cost, low stability, poor reusability and difficulty of their use in continuous reactors. Therefore, alternative technology is required for economizing system and using enzymes at large scale; enzyme immobilization is a preferred technology to apply enzymes at industrial level in batch processes as well as in continuous reactors [17,18]. Since the advent of enzyme immobilization technology, a large number of methods have been developed to immobilize cellulolytic and other enzymes and many of them have successfully been applied at commercial level [19]. Moreover, the immobilization of cellulolytic enzymes on the surface of bulk support via adsorption or covalent attachment or by entrapment is not suitable particularly for cellulases, a major enzyme required for cellulose hydrolysis. The substrate for cellulase is insoluble and very large macromolecule, and thus it creates steric hindrances in the binding with the active site of enzyme. There are also some more demerits of traditional immobilization of cellulases such as poor yield of immobilization in case of surface binding and problem of accessibility of substrate for entrapped and microencapsulated enzymes [20,21]. Figure 2 represents steric hindrances between active site of cellulase bound to bulk and nanosupport and cellulose substrate. The separation of immobilized enzyme from reaction medium is also problematic due to insoluble nature of substrate, cellulose.

    Nanoparticles (NPs) have unique properties such as large surface area and their surfaces can be easily modified for the purpose of enzyme immobilization. NP supports have demonstrated their potential in immobilizing enzymes in high yield and the presence of NP-support with enzymes poses least chances of steric hindrances [22,23]. In one of the study, the author’s group has investigated the immobilization of β-galactosidase on native and nano ZnO, the immobilization yield and stability of this enzyme on nano ZnO was remarkably higher compared to immobilization obtained on native ZnO [24]. Enzymes immobilized on nanosupprts have demonstrated their applications in analy

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