Polyelectrolyte enzyme system

A solution of any polyelectrolyte-enzyme system might be considered as consisting of two phases in equilibrium, although, within limits, the polyelectrolyte is soluble. Owing to the local electrostatic potential, the inner polyelectrolydc phase, or environment, possesses its own local physicochemical parameters which differ from those of the bulk phase. 

Figure 2.1 Chemical structure of osmium derivatized polyelectrolyte—enzyme system developed by Heller. Taken from Ref. [37].

If we consider a system polyelectrolyte-enzyme, the catalytic implications of the polyelectrolyte theory become evident when Eq. (39) is applied to protons, substrates, and inhibitors (as long as these are charged molecules). Equation (39) shows that the average concentration of protons in the polyelectrolytic environment is different from that of the bulk medium ... 

Capsule membranes with an adsorbed polyelectrolyte layer through which the permeation of solutes is dramatically altered in response to small changes in pH would be useful in constructing a functional encapsulated enzyme system in which the initiation/termination of an enzymatic reaction could be controlled. PSt microcapsules with copoly(MA, St) or PIE seem to be well suited for this purpose, since their permeability alters rapidly over a very narrow pH range as a result of changes in the configuration of the adsorbed polyion. The present section describes the on/off control of an enzyme reaction using pH-sensitive PSt microcapsules with copoly(MA, St). 

The immobilization of enzymes with the formation of insoluble forms is usually intended for the development of specific catalysts for technical purposes. Here, we consider another medico-biological problem of the preparation of insoluble enzymatic systems based on crosslinked polyelectrolytes, used in the replacement therapy for oral administration. 

The polyelectrolyte covalently functionalized with reactive groups may be viewed as an enzyme-like functional polymer or as a molecular reaction system in the sense that it has both reactive centers and reaction rate-controlling microenvironments bound together on the same macromolecule. 

Equations 2.26 and 2.27 carmot be solved analytically except for a series of limiting cases considered by Bartlett and Pratt [147,192]. Since fine control of film thickness and organization can be achieved with LbL self-assembled enzyme polyelectrolyte multilayers, these different cases of the kinetic case-diagram for amperometric enzyme electrodes could be tested [147]. For the enzyme multilayer with entrapped mediator in the mediator-limited kinetics (enzyme-mediator reaction rate-determining step), two kinetic cases deserve consideration in this system in both cases I and II, there is no substrate dependence since the kinetics are mediator limited and the current is potential dependent, since the mediator concentration is potential dependent. Since diffusion is fast as compared to enzyme kinetics, mediator and substrate are both approximately at their bulk concentrations throughout the film in case I. The current is first order in both mediator and enzyme concentration and k, the enzyme reoxidation rate. It increases linearly with film thickness since there is no... 

Polyelectrolyte multilayer microspheres, prepared by alternating adsorption of dextran sulfate and protamine on melamine formaldehyde cores followed by the partial decomposition of the core, were used to immobilise the peroxidase and glucose oxidase. Retention of enzymic activity of the peroxidase/glucose oxidase system incorporated into the microspheres was demonstrated. These bienzyme system immobilised in the microspheres can be applied for kinetic glucose assays [ 156]. 

A negative photoresist, SU-8 (Microchem), was used in the microreactor mold process for preparing the PDSM-E microreactors. When exposed to ultraviolet light, material may be removed via a wet etching process leaving high-definition features in micrometer dimensions. Additionally, a microreactor has been constructed in silicon onto which layer-bylayer self-assembled polyelectrolytes and enzymes are deposited. This system is being used for comparison with the PDMS-E system performance. 

Polyelectrolyte complexes can be prepared in a desired range of mass, size and structure density. The behavior of the PECs can be controlled by external parameters such as the ionic strength, the pH of the medium or the temperature. Therefore, such complexes should be of great interest as potential carrier systems for drugs, enzymes, or DNA because charged species can easily be integrated into the complex particles. 

Effect of pH. If ionic strength changes cannot render PAH/PSS capsules permeable to larger species (e.g., macromolecules, enzymes, nanoparticles), then manipulation of pH or solvent polarity can be used. The point about the (PAH/PSS) system is that PSS is a strong polyelectrolyte and remains fully ionized, whereas PAH is a weak polyelectrolyte and so its dissociation is dependent on pH. 

Enzyme based micron sized sensing system with optical readout was fabricated by co-encapsulation of urease and dextran couple with pH sensitive dye SNARE-1 into polyelectrolyte multilayer capsules. The co-precipitation of calcium caibonate, urease, and dextran followed up by multilayer film coating and Ca- extracting by EDTA resulted in formation of 3.5-4 micron capsules, what enable the calibrated fluorescence response to urea in concentration range from 10 to 10 M. Sensitivity to urea in concentration range of 10 to 10 M was monitored on capsule assemblies (suspension) and on single capsule measurements. Urea presence can be monitored on single capsule level as illustrated by confocal fluorescent microscopy. 

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