Enzyme carrier, polymeric

While peptide antibiotics are synthesized according to enzyme-controlled polymerization patterns, both proteins and nucleic acids are made by template mechanisms. Tire sequence of their monomer emits is determined by genetically encoded information. A key reaction in the formation of proteins is the transfer of activated aminoacyl groups to molecules of tRNA (Eq. 17-36). Tire tRNAs act as carriers or adapters as explained in detail in Chapter 29. Each aminoacyl-tRNA synthetase must recognize the correct tRNA and attach the correct amino acid to it. The tRNA then carries the activated amino acid to a ribosome, where it is placed, at the correct moment, in the active site. Peptidyltransferase, using a transacylation reaction, in an insertion mechanism transfers the C terminus of the growing peptide chain onto the amino group of... 

Figure 13 shows the reaction of the double bond with Mercury (II) acetate (50). In a fast reaction the double bonds at the surface react. Subsequently controlled by a slow diffusion process, the double bonds in the interior of the particle react. The specific surface of these systems is 200 to 300 m2/g. As enzyme carriers they should be well-suited, as support for polymeric reagents more knowledge about the possibility of localizing the reaction at the surface is needed. 

The catalytic behavior of enzymes in immobilized form may dramatically differ from that of soluble homogeneous enzymes. In particular, mass transport effects (the transport of a substrate to the catalyst and diffusion of reaction products away from the catalyst matrix) may result in the reduction of the overall activity. Mass transport effects are usually divided into two categories - external and internal. External effects stem from the fact that substrates must be transported from the bulk solution to the surface of an immobilized enzyme. Internal diffusional limitations occur when a substrate penetrates inside the immobilized enzyme particle, such as porous carriers, polymeric microspheres, membranes, etc. The classical treatment of mass transfer in heterogeneous catalysis has been successfully applied to immobilized enzymes I27l There are several simple experimental criteria or tests that allow one to determine whether a reaction is limited by external diffusion. For example, if a reaction is completely limited by external diffusion, the rate of the process should not depend on pH or enzyme concentration. At the same time the rate of reaction will depend on the stirring in the batch reactor or on the flow rate of a substrate in the column reactor. 

Enzymes are covalently immobilized primarily onto the surface of the membrane exposed to the feed solution, known as the "active side" of the asymmetric membrane. In general, it is not clear whether reaction between enzymes and polymeric membranes via coupling agents simply results in enzyme attachment to the membrane, or if it leads to an enzyme-carrier network inside the polymer matrix. For the sake of simplicity let us assume that asymmetric membranes are used, that suitable active groups are available on the polymeric surface and that the membrane molecular weight cut-off is such that the active layer is enzyme-impermeable. In this way, even though their activity is often drastically reduced, surface bound enzymes are in close proximity to the substrate solution-thus reducing the mass transfer resistance to that associated with the boundary layer. When enzymes are covalently immobilized in the... 

However, to our knowledge, most previous studies of enzyme-catalyzed polymerizations have avoided temperatures > 90 oC, which is likely due to thermal deactivation of enzyme catalyst (13-15). It has been found that enzyme immobilization can improve the stability and recyclablity of native enzyme (16). Silica particles, activated by methanesulfonic acid, are effective and economic inorganic carriers for enzyme immobilization (17). Herein, we present a minireview of our works about immobilized porcine pancareas lipase on silica particles (IPPL) for polymer synthesis, such as polycarbonates, polyesters, polyphosphates and their copoljmiers. 

The use of a carrier or polymeric matrix to immobilize enzymes introduces a large noncatalytic component into the system which has the potential to interfere with the catalytic properties of the enzyme and reduce its activity compared to the same mass of free enzyme. Although this disadvantage is balanced by the reusability of immobilized enzymes, it would be even more beneficial if the activities of immobilized enzymes could match those of free enzymes. Carrier-free systems, in which enzyme molecules are linked to each other to form large complexes, may provide a solution to this problem. In a carrier-dependent system, up to 99.9% of the mass is taken up by the noncatalytic matrix. In noncarrier systems, 100% of the complex has the potential to retain catalytic activity. 

Hicke, HG, Becker, M, Paulke BR and Ulbricht, M (2006), Covalently coupled nanoparticles in capillary pores as enzyme carrier and as turbulence promoter to facilitate enzymatic polymerizations in flow-through enzyme-membrane reactors , / Membr Sci, 282,413-422. 

Novel chiral. separations using enzymes and chiral surfactants as carriers have been realized using facilitated transport membranes. Japanese workers have reported the synthesis of a novel norbornadiene polymeric membrane with optically active pendent groups that show enantio.selectivity, which has shown promi.se in the. separation of propronalol. 

Following this cleavage in principle, amines (bound as urethanes), alcohols (bound as carbonates), and carboxylic acids (bound as esters) can be detached from the polymeric carrier. The substrate specificity of the enzyme guarantees that only the intended ester is cleaved. 

Biological principles are also used in enzyme electrodes, where the sensor (usually an ion-selective electrode) is covered by a polymeric carrier containing an enzyme [32]. The determinand reacts in the enzyme layer yielding a product that causes a signal in the sensor. The bacterium electrode is based on a similar principle [84], as are electrodes using tissue in place of the enzyme layer [2]. 

The rapid development of biotechnology during the 1980s provided new opportunities for the application of reaction engineering principles. In biochemical systems, reactions are catalyzed by enzymes. These biocatalysts may be dispersed in an aqueous phase or in a reverse micelle, supported on a polymeric carrier, or contained within whole cells. The reactors used are most often stirred tanks, bubble columns, or hollow fibers. If the kinetics for the enzymatic process is known, then the effects of reaction conditions and mass transfer phenomena can be analyzed quite successfully using classical reactor models. Where living cells are present, the growth of the cell mass as well as the kinetics of the desired reaction must be modeled [16, 17]. 

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