Enzyme carriers

An immobilized enzyme-carrier complex is a special case that can employ the methodology developed for evaluation of a heterogeneous cat ytic system. The enzyme complex also has external diffusional effects, pore diffusional effects, and an effectiveness factor. When carried out in aqueous solutions, heat transfer is usually good, and it is safe to assume that isothermal conditions prevail for an immobihzed enzyme complex. 

DIFFUSION AND REACTION IN A POROUS ENZYME CARRIER STEADY-STATE SPLIT BOUNDARY SOLUTION... 

The Na ion concentration within the cell is maintained low, due to activity of an enzyme known as the Na+/K+ ATPase. This enzyme/carrier is present in the plasma membrane. It is an antiport system that transports three Na+ ions out of the cell and two K+ ions into the cell, for each molecule of ATP that is hydrolysed (Figure 5.10). It is responsible for maintaining a low Na+ ion concentration but a high K+ ion concentration within the ceU. Its constant activity in many it not all cells requires constant ATP hydrolysis, which accounts for more than 10% of the resting energy expenditure of an adult. 

The monolithic stirrer reactor (MSR, Figure 2), in which monoliths are used as stirrer blades, is a new reactor type for heterogeneously catalyzed liquid and gas-liquid reactions (6). This reactor is thought to be especially useful in the production of fine chemicals and in biochemistry and biotechnology. In this work, we use cordierite monoliths as stirrer blades for enzyme-catalyzed reactions. Conventional enzyme carriers, including chitosan, polyethylenimine and different are used to functionalize the monoliths. Lipase was... 

Petrikovics I, McGuinn WD et al (2000) In vitro studies on stericaUy stabUized liposomes (SL) as enzyme carriers in organophosphoms (OP) antagonism. Dmg DeUv 7(2) 83-89... 

Binding enzymes to solid supports can be achieved via covalent bonds, ionic interactions, or physical adsorption, although the last two options are prone to leaching. Enzymes are easily bound to several types of synthetic polymers, such as acrylic resins, as well as biopolymers, e.g., starch, cellulose [52], or chitosan [53,54]. Degussa s Eupergit resins, for example, are used as enzyme carriers in the production of semisynthetic antibiotics and chiral pharmaceuticals [55], Typically, these copolymers contain an acrylamide/methacrylate backbone, with epoxide side groups... 

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. 

Cao L, van Langen L, Sheldon RA (2003) Immobilised enzymes carrier-bound or carrier-free Curr Opin Biotechnol 14 387-394... 

Proton -Bronsted acid Metal ion -Lewis acid Anion -Host -Electrophile -Hydrogen bond donor -Oxidant -Charge transfer donor -Ion -Radical -Solute -Adsorbent -Enzyme -Carrier (protein) -Receptor -Antibody -... 

The 12 investigations compiled here deal mostly with functional investigations in the food area. Three chapters discuss soy proteins, relating the effects of heat, specific solvents, and enzyme activity on structure and functional properties. Single chapters are concerned with the proteins of wheat, milk, and yeast, respectively, as well as specific crosslinking effects and, enzyme-carrier interactions. Other chapters contrast general functional properties of different proteins. 

Cao, L., Van Langen, L., and Sheldon, R. 2003. Immobilised enzymes Carrier bound or carrier-free Current Opinion in Biotechnology, 14 387-94. 

In addition to anion and cation exchangers as enzyme carriers it has been demonstrated that mixed ion exchange supports can be used for binding enzymes with both acid and amino groups at pH values close to the isoelectric point, such as penidUin G acylase from Escherichia coli (Figure 2.4) ]49]. 

Nevertheless, the selectivity of action of many of these toxins means they have been harnessed in medical therapeutics (more so in experimental pharmacology and physiology). Toxins that have been, or still are, used in medicine include atropine and hyoscine, botulinum toxin, colchicine, digitalis alkaloids, eserine, morphine, ouabain, picrotoxin, strychnine, veratridine, vinca alkaloids and many more. These work by an action at a defined molecular site, whether ion channel, neurotransmitter receptor, enzyme, carrier molecule (pump) or intracellular organelle. Several of these particular examples have their most obvious effects on neurotransmission, and are dealt with under neurotoxins. 

Data related to particle size and binding capacity are of major importance. The binding capacity of enzyme carriers for proteins is 0.1 -10% of the carrier weight. Prefabricated carriers are provided with 100-1000 pm in diameter. Spherical carriers such as Eupergit C particles have an average diameter of 160 pm [87]. 

In summary, PCBs can affect a wide variety of endocrine systems by directly affecting the components of the endocrine system such as hormones, metabolic enzymes, carrier proteins, receptors, endocrine glands, and feedback regulation systems. Effects on these components can lead to alterations in neurodevelopment, reproduction, and in induction of endocrine-sensitive tumors. 

Adenylate cyclase/cychc adenosine monophosphate (cAMP). Production of cAMP activates various protein kinases, which in turn influence the function of various enzymes, carriers, etc. Adenylate cyclase can either be stimulated (excitation) or inhibited (inhibition) (Fig. 1.4). 

In packed bed reactors the enzyme-catalyzed reaction is carried out in a column of 100 pl-10 ml volume. The column is filled with tiny particles bearing the immobilized enzyme. The continuously formed reaction product is indicated colorimetrically or electrochemically. Enzyme carrier materials with advantageous flow behavior are porous glass with pores of a defined size, organic polymers, like nylon powder, and inorganic polymers. 

When the mass of carrier material is large relative to that of the enzyme, the physical and chemical properties of the carrier (Table 6-5) will, in large part, determine properties of the resultant immobilized enzyme. Often, the carrier will impart mechanical strength to the enzyme, allowing repetitive recovery by simple filtration of the solid particles and reuse of the enzyme. The degree of porosity and pore volume will determine the resistance to diffusion and molecular size selectivity of the biocatalyst. When used in non-aqueous media, dispersion of the enzyme over a large surface area can greatly increase its activity. Table 6-3 summarizes many of the key properties and considerations for enzyme carrier materials. 

Table 6-3. Summary of properties and considerations for enzyme carriers.

Loading capacity 0.1% to 10% w/w Enzyme/carrier ratio, volumetric activity... 

For enzyme economy it may be possible to immobilize the lytic enzymes on some type of solid carrier and to pass a yeast slurry over the immobilized enzyme. Macmillan et al. (138) experimented with collagen as the enzyme carrier, but since the enzymes in this system were not covalently linked they were slowly leached from the carrier. 

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... 

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