Stability of immobilized enzymes

Solutions of surfactant-stabilized nanogels share both the advantage of gels (drastic reduction of molecular diffusion and of internal dynamics of solubilizates entrapped in the micellar aggregates) and of nonviscous liquids (nanogel-containing reversed micelles diffuse and are dispersed in a macroscopicaUy nonviscous medium). Effects on the lifetime of excited species and on the catalytic activity and stability of immobilized enzymes can be expected. 

This field summarizes general information on stability, e.g., increased stability of immobilized enzymes, stabilization by SH-reagents, detergents, glycerol or albumins etc. 

This configuration improved the selectivity and productivity of the biocatalytic system as well as its catalytic stability, confirming that the observed inversion relationship between activity and stability of immobilized enzyme is not a general rule. 

Takahashi H, Li B, Sasaki T et al (2000) Catalytic activity in organic solvents and stability of immobilized enzymes depend on the pore size and surface characteristics of mesoporous silica. Chem Mater 12 3301-3305... 

Fernandez-Lafuente, R., Rosell, C. M., Caanan-Haden, L., Rodes, L., Guisan, J.M. (1998) Stabilization of immobilized enzymes against organic solvents complete hydrophilization of enzymes environments by solid-phase chemistry with poly-functional macromolecules, Prog. Biotechnol. 15 (Stability and Stabilization of Biocatalysis), 405-410. 

A variety of physical and chemical methods have evolved for immobilizing enzymes on or within solid supports. Kennedy and Cabral employed a variation of the scheme in Fig. 1 to classify techniques for immobilization of enzymes.f Judicious choice of the support is essential not only for the stability of immobilized enzymes, but also for the operational characteristics of the device containing the immobilized enzyme and the economic viability of the intended application. The discussion below and the information in Table 1 indicate some of the criteria employed in selecting a mode of immobilization. 

Fig. 8 shows the denaturation of an enzyme in a hydrogel. This example shows the possibility to investigate the thermodynamic stability of immobilized enzymes in microgels. 

Operational stability of immobilized enzymes and microbial cells is high, especially of that treated with appropriate hardening agents. 

Abian O, Mateo C, Femandez-Loiente G et til. (2001) Stabilization of immobilized enzymes against water-soluble organic cosolvents tmd generation of hyperhydrophiUc microenvironments surrounding enzyme molecules. Biocateil Biotransform 19 489-503... 

For biotechnological applications, synthetic membranes entrapping enzymes, bacteria, or animal cells are used in membrane bioreactors disclosing new important developments mainly due to the increased stability of immobilized enzymes, the possibility of their continuous reuse and the absence of pollution of the products. Membrane bioreactors are of great interest as well for the possibility of continuously removing metabolites whose presence in the reaction environment could reduce the productivity of the reactor. 

For water-miscible solvents, the correlation of the stability of immobilized enzyme with physicochemical parameters of organic solvent was investigated. Two parameters, log P (the partition coefficient between the n-octanol-water phases, i.e., reflecting the hydrophobicity of organic solvents) and Et (30) (the polarity of organic solvents), were chosen. As shown in Fig. 13 [59], either the log P or Et (30) value was found to be applicable to correlate the stability of the immobilized enzyme in the water-miscible organic solvents. Therefore, the inactivation of the immobilized enzyme in water-miscible organic solvents was affected by the extent to which they remove water from the surface of the enzyme molecule. 

Dried cross-linked (-l-)-Y-lactamase mixed with controlled pore [163] glass in a 1 1 ratio stability of immobilized enzyme for 8h at 80 °C kinetic constants determined in the microreactor Glucose oxidase or choline oxidase were separately immobilized [162] on the surface of PEI coated monolith. Method is simple based on preparation of monolith with controlled porosity low pressure drop, mass transfer limitations avoided enzymes immobilized on PEI-activated surface of monolity through electropositive (PEI and electronegative (enzyme) nature... 

Both the purity of the enzyme and the hydrophobicity or polarity of the solvent are important parameters for the stability of enzymes. Wehtje et al. [108] found an interesting process for stabilization of immobilized enzymes. They added stabilizing agents (polyethylene glycol, gelatin, casein, tryptone, peptone, or albumin) when immobilizing the enzyme on the support. 

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