Functional immobilized enzymes

During operation, the immobilized enzyme loses activity. Most commercial enzymes show decay as a function of time (Eig. 12). The glucose isomerase ia a reactor is usually replaced after three half-Hves, ie, when the activity has dropped to around 12.5% of the initial value. The most stable commercial glucose isomerases have half-Hves of around 200 days ia practical use. To maintain the same fmctose content ia the finished symp, the feed-flow rate is adjusted according to the actual activity of the enzyme. With only one isomerization reactor ia operation, the result would be excessive variations ia the rate of symp production. To avoid this, several reactors at different stages ia the cycle of enzyme decay are operated ia combiaation. 

Concerning function integration, for example, micro-flow membrane reactors can exhibit similar process intensification, as shown already for their large-scale counterparts [75]. Separation columns for proteomics, immobilizing enzymes, utilize the large surface-to-volume ratios. Surface tension differences can guide and transport liquids selectively. 

The porosity of hybrid nanocomposites provides access of the substrates to immobilized enzyme and their proper functioning. It is attributable to the absence of volume shrinkage of synthesized materials after their preparation. Although the compacting does not occur as in the common two-stage processes (Figure 3.7), enzyme macromolecules are held inside the silica matrix and not easily washed out of it. 

Addition of third components to nanohybrids of proteins and mesoporous materials sometimes brings advantages in their functions. Kim, Hyeon, and coworkers immobilized enzyme molecules together with magnetite (Fe304) nanoparticles in hierarchically ordered, mesocellular, mesoporous silica (HMMS) (Figure 4.25)... 

It can be seen from Eq. (5) that the maximum possible concentration on the surface, c, influences significantly the transport rate. This parameter is a function of the available surface area as well as of the density of the reactive sites. Because of that, the matrix structure plays a very important role in such adsorp-tion/desorption processes. In the case of biological reactions, where the chemical conversion is performed by immobilized enzymes, the immobilization also plays an important role in order to achieve an optimal enzyme density on the reactive surface. 

A further advantage, as described by Thomas et al. [19], is the possibility of protein identification that follows the functional characterization of the enzyme. The activity of an enzyme is initially determined by following the substrate consumption and product formation in the first assay (Fig. 8.10). Since no matrix components are present in the sample spot, the immobilized enzyme is then directly... 

Existing uses of proteases in foods have been discussed in the foregoing section. Expanding such applications in the future depends upon our ability to control both the processes themselves and their costs. The development of continuous reactors utilizing free or immobilized enzymes will address each of these constraints. Furthermore, our understanding of the chemical basis for the various functional properties of proteins must be expanded... 

The wide variety of enzymes available gives for promise enzymatic derivatization to become a potent analytical tool in the future. Better understanding and theoretical formulations will lead to commercial availability of immobilized enzymes and consequently to more ready use of them. Since in such systems a low content of organic cosolvent in the mobile phase can only be tolerated (whereas a compromise has to be made as far as the optimum mobile phase pH is concerned), artificial enzymes, which are synthetic polymer chains having functional groups that mimic the biocatalytic activity of natural enzymes, are currently being synthesized and investigated as a means to overcome such limitations (276). 

A renewed interest in this research field may lead to the construction of functional immobilized biocatalysts that surpass the conventional definition, or usually credited advantages, of immobilized biocatalysts with regard to their capabilities as catalysts [22-24], i.e. immobilized enzyme systems in which, for example, an enzymatic process can be controlled by externally applied stimuli such as light, electric fields, pH, temperature, and mechanical force. In such cases, what is crucial in system construction is not to rely on a possible... 

HOLLOW-FIBER MEMBRANES. A hollow-fiher membrane is a capillary having an inside diameter of - inn and an outside diameter < I mm and whose wall functions as a semipermeahlc membrane. The fibers can he employed singly or grouped into a bundle which may contain tens of thousands of fibers and up to several million libers as in reverse osmosis (Fig. 11. In most eases, hollow fibers are used as cylindrical membranes that permit selective exchange of materials across (heir walls. However, they can also he used as containers to effect the controlled release of a specific material, or as reactors to chemically modify a permeate as il diffuses through a chemically activated hollow-liher wall. e g., loaded with immobilized enzyme. 

The versatility of water-soluble polyphosphazenes is in the variations in the structures that can be prepared. Structures with a low glass-transition temperature backbone can be modified with a variety of versatile side units. These may find use in solid polymeric ionic conductors, as a means to entrap and immobilize enzymes with retention of enzymic activity, and in biological functions as hydrogels with the capability of exhibiting biocompatibility and... 

Covalent Attachment The covalent attachment of enzyme molecules via nonessential amino acid residues (that is, amino acids minus water) to water-insoluble, functionalized supports are the most widely used method for immobilizing enzymes. Functional groups of the nonessential amino acid residues that are suitable for the immobilization process are free a-, /3-, or y-carboxyl groups, a- or /3-amino groups, and phenyl, hydroxyl, sulfhydryl, or imidazole groups.2... 

Already active polymers such as maleic anhydride copolymers will be simply mixed with enzymes to produce immobilized enzymes. Normally, natural or synthetic polymers need to be activated by treating them with reagents before adding the enzyme. The activation involves the chemical conversion of a functional group of the polymer. The enzyme s active site should not be involved in the attachment, in which case the enzyme would lose its activity upon immobilization. 

Fig. 3.1 Several different methods for producing immobilized enzymes with multifunctional reagents (a) enzymes are adsorbed on the surface-active support followed by inter-molecular cross-linking, (b) functional groups are intro-duced on the support to react covalently with enzymes, and (c) enzymes are cross-linked intermolecularly.

Surface-functionalized polymers are also of interest for uses in biochemical reactors, and biomedical sensors. The immobilization of enzymes on a polymer surface is an important example. Numerous reasons exist for attempting to immobilize enzymes on the surfaces of polymers. For one thing, immobilization often enhances the length of time over which the protein maintains its catalytic activity, compared to the same... 

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