Biocatalysis limits

BioCataly- tics BioCatalytics Inc. 39 Congress Street, Suite 303 Pasadena, CA 91105-3022 USA Tel. +1 (626) 229-0588 Fax +1 (626) 535-9465 Email info biocatalytics.com http //www.biocatalytics.com Biocatalytical process development. Experimental enzymes for biocatalysis. Limited production capacity. Distributor for Roche in USA and Canada. 

Jttlich Enzyme Products Juelich Enzyme Products GmbH Karl-Heinz-Beckurts-Str. 13 D-52428 Jiilich Germany Tel. +49 (2461) 348188 Fax +49 (2461) 348186 E-mail juelichep aol.com http //www. juelich-enzyme.com Experimental enzymes for biocatalysis. Limited enzyme production capacity. 

These perspectives allow us to conclude that the constant rise of importance of biocatalysis in industrial processes is secured for years to come, and is limited only by further recognition from industrial society. 

If we extend this vision to the biocatalysis at silicon, as reported in some of the recent papers,641 642 and continue learning from nature how to be bioinspired in making nanoporous silicas and other membranes, then, what seemed to be true in Goody s remark about liquid crystals, might also apply to the whole field of silicones new field lies open for the development of materials for which their design is only limited by human imagination. 256... 

Although the focus here is on the integration of biocatalysis with chemocataly-sis (bio-chemo cascades) for carbohydrates as renewable feedstocks, some representative examples (from laboratory to industrial scale) of both bio-bio and chemo-chemo cascades are also given below for comparison of their relative scope and limitations. 

Biocatalysis has traditionally been performed in aqueous environments, but this is of limited value for the vast majority of nonpolar reactants used in chemical synthesis. For a long time it was assumed that all organic solvents act as denaturants, primarily based on the flawed extrapolation of data obtained from the exposure of aqueous solutions of enzyme to a few water-miscible solvents, such as alcohols and acetone, to that of all organic sol vents. 

A major cause of suboptimal activity in organic solvent results from the removal of essential water during enzyme dehydration. All enzymes require some water in order to retain activity through the provision of conformational flexibihty. Particularly in the case of lipases, the amount of water can be so low that it appears that none is required. For example, following the development of suitable techniques to analyse low water concentrations, it has been reported that the lipase from Rhizomucor miehei retains 30 % of its optimum activity with as little as two or three water molecules per molecule of enzyme.Owing to the apparent absence of water in some exceptional cases, the term biocatalysis in anhydrous solvent is commonly used, although in the vast majority of cases a monolayer of water is required for optimal activity (although this is often stUl well below its solubility limit in water-immiscible solvent). ... 

Because enzymes are insoluble in organic solvent, mass-transfer limitations apply as with any heterogeneous catalyst. Water-soluble enzymes (which represent the majority of enzymes currently used in biocatalysis) have hydrophilic surfaces and so tend to form aggregates or stick to reaction vessel walls rather than form the fine dispersions that are required for optimum efficiency. This can be overcome by enzyme immobilization, as discussed in Section 1.5. 

Immobdized enzymes are frequently used in biocatalysis to overcome limitations such as ... 

An ionic liquid can be used as a pure solvent or as a co-solvent. An enzyme-ionic liquid system can be operated in a single phase or in multiple phases. Although most research has focused on enzymatic catalysis in ionic liquids, application to whole cell systems has also been reported (272). Besides searches for an alternative non-volatile and polar media with reduced water and orgamc solvents for biocatalysis, significant attention has been paid to the dispersion of enzymes and microorganisms in ionic liquids so that repeated use of the expensive biocatalysts can be realized. Another incentive for biocatalysis in ionic liquid media is to take advantage of the tunability of the solvent properties of the ionic liquids to achieve improved catalytic performance. Because biocatalysts are applied predominantly at lower temperatures (occasionally exceeding 100°C), thermal stability limitations of ionic liquids are typically not a concern. Instead, the solvent properties are most critical to the performance of biocatalysts. 

Promising developments of ionic liquids for biocatalysis reflect their enhanced thermal and operational stabilities, sometimes combined with high regio- or enantioselectivities. Ionic liquids are particularly attractive media for certain biotransformations of highly polar substrates, which cannot be performed in water owing to equilibrium limitations 297). 

Enzyme catalysis of reactions (biocatalysis) is a branch of biotechnology (Hauer 1999 Crameri 1999). The superiority of biocatalytic methods of synthesis, particularly if carried out in a continuum (Orsat 1999), is often manifestly clear, only limited by the cost of replacing the old chemical plants (Pachlatko 1999 Schmid 2001). Illustrative examples of biocatalytic plants are illustrated in Chart 14.2. 

The scope and limitations of biocatalysis in non-conventional media are described. First, different kinds of non-conventional reaction media, such as organic solvents, supercritical fluids, gaseous media and solvent-free systems, are treated. Second, enzyme preparations suitable for use in these media are described. In several cases the enzyme is present as a solid phase but there are methods to solubilise enzymes in non-conventional media, as well. Third, important reaction parameters for biocatalysis in non-conventional media are discussed. The water content is of large importance in all non-conventional systems. The effects of the reaction medinm on enzyme activity, stabihty and on reaction yield are described. Finally, a few applications are briefly presented. 

In chapter 8 the most generally nsed kinetic eqnations for describing the consnmption of snbstrate as a resnlt of biocatalysis have been given and/or derived. In biocatalysis, in the absence of limitation of the rate of consnmption by diffusion of substrate, the Michaelis-Menten equation usually is a good description ... 

Also in case of diffusion-limited reactions where the overall effectiveness factor is used to describe the effect of diffusion on the rate of biocatalysis, the mathematics are the same as in the case of the batch reactor. Substitution of Equation (11.56) in Equation (11.23) thus yields ... 

Thus the use and practice of biocatalysis at full scale has waxed and waned over the years. In the past, one factor limiting the use of biocatalysis has been the availability of a variety of enzymes and the time taken to refine/evolve enzymes for specific industrial apphcations. Hydrolytic enzymes such as lipases and proteases designed for other industrial uses such as detergents and food processing have always been available in bulk, and indeed used by process chemists. 

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