Biocatalysis types

In the last decade, biocatalysis in nonaqueous media, using hydrolases, has been widely used for organic chemists. The possibilities that these biocatalysts offer for the preparation of different types of organic compounds, depending upon the nucleophile... 

In this volume not all stress types are treated. Various aspects have been reviewed recently by various authors e.g. The effects of oxygen on recombinant protein expression by Konz et al. [2]. The Mechanisms by which bacterial cells respond to pH was considered in a Symposium in 1999 [3] and solvent effects were reviewed by de Bont in the article Solvent-tolerant bacteria in biocatalysis [4]. Therefore, these aspects are not considered in this volume. Influence of fluid dynamical stresses on micro-organism, animal and plant cells are in center of interest in this volume. In chapter 2, H.-J. Henzler discusses the quantitative evaluation of fluid dynamical stresses in various type of reactors with different methods based on investigations performed on laboratory an pilot plant scales. S. S. Yim and A. Shamlou give a general review on the effects of fluid dynamical and mechanical stresses on micro-organisms and bio-polymers in chapter 3. G. Ketzmer describes the effects of shear stress on adherent cells in chapter 4. Finally, in chapter 5, P. Kieran considers the influence of stress on plant cells. 

In a biphasic medium, two situations are distinguished for the reaction. Biocatalysis occurs at the liquid-liquid interface [42,43] or in the bulk of the aqueous phase [25,27]. Models have been developed for both types, and interaction between mass transfer and enzyme-catalyzed reactions has been also studied. 

In addition to the studies studied by use and presented above, we will briefly present some examples from other research groups. Due to the flexibility of the ONIOM scheme, it can be used to address many different types of problems in biocatalysis. This is by no means an extensive listing, but it illustrates main types of ONIOM applications to date. 

Thus, the organoclay armoured-proteins should have diverse applications in areas such as biosensing, biocatalysis and bioelectronics. Moreover, the experimental procedure is extremely facile and could, in principle, be applied to many types of biomolecules, including bio-macromolecules such as DNA. 

Membranes can be used as a matrix for immobilization of a catalyst. Four basic types of catalysts are relevant (a) enzymes and (b) whole cells for biocatalysis (c) oxides and (d) metals for nonbiological synthesis. Biocatalysts will be considered first since their immobilization in (or on) the membrane was explored much earlier. Five techniques have been studied in varying degrees. They are (1) enzyme contained in the spongy fiber matrix ... 

It was reported that PEGylated lipase entrapped in PVA cryogel could be conveniently used in organic solvent biocatalysis [279], This method for enzyme immobilization is more convenient in comparison to other types of immobilization that take advantage of enzyme covalent linkage to insoluble matrix, since the chemical step which is time consuming and harmful to enzyme activity is avoided. The application of this catalytic system to the hydrolysis of acetoxycoumarins demonstrated the feasibility of proposed method in the hydrolysis products of pharmaceutical interest and to obtain regioselective enrichment of one of the two monodeacetylated derivatives. 

Whereas several areas of biocatalysis - in particular the use of easy-to-use hydrolases, such as proteases, esterases and lipases - are sufficiently well research to be applied in every standard laboratory, other types of enzymes are still waiting to be discovered with respect to their applicability in organic-chemistry transformations on a preparative scale. This latter point is stressed in this volume, which concentrates on the newcomer-enzymes which show great synthetic potential. 

An interesting example of biocatalysis and chemical catalysis is the synthesis of a derivative of y-aminobutyric acid (GABA) that is an inhibitor for the treatment of neuropathic pain and epilepsy (Scheme 10.4). The key intermediate is a racemic mixture of cis- and trons-diastereoisomer esters obtained by a hydrogenation following a Horner-Emmons reaction. The enzymatic hydrolysis of both diaste-reoisomers, catalyzed by Candida antarctica lipase type B (CALB), yields the corresponding acid intermediate of the GABA derivative. It is of note that both cis- and trans-diastereoisomers of the desired enantiomer of the acid intermediate can be converted into the final product in the downstream chemistry [10]. 

Thus far only three reports regarding the directed evolution of enantioselective EHs have appeared 95,96,143), notwithstanding the fact that these enzymes, even as wild types, constitute important catalysts in synthetic organic chemistry 7-12,144,145). Indeed, since two EHs became commercially available recently, this type of biocatalysis offers exciting prospects for the practicing organic chemist. 

Originally almost all apphcations of biocatalysis involved hydrolytic reactions, except a few, such as L-sorbose and ephedrine manufacture (Turner, 1994). Hydrolases still are the main conunercial enzyme class, but nowadays a much wider range of reactions is being applied, either on a conunercial scale or on a lab scale. The most important reaction types are reviewed in chapter 2. 

The range of commercial applications types of biocatalysis always has been veiy wide, and is continuously expanding further. Therefore, the applications that are treated in this book have been divided in two types ... 

After the publication of the first edition of Applied Biocatalysis some five years ago, this field has rapidly been developing. This is evident from the number and types of new applications, but also from the state of the art for some of the important techniqnes, such as protein engineering and the use of non-conventional media, for example. 

Further progress will most likely include other types of reactions and new types of polymers as well as new solvent-stable nanofiltration membranes. Another promising field is the combination of chemo- and biocatalysis in cascade reactions... 

Biocatalysis in ionic liquids was first reported in 2000 [7, 8, 9]. The early work involved ionic liquids composed of a 1,3-dialkylimidazolium or N-alkylpyridinium cation and a weakly-coordinating anion (Figure 10.1). More recently, attention is shifting toward new structural types. A number of reviews of this rapidly expanding subject have appeared [10, 11, 12, 13, 14]. 

Biotechnology and biocatalysis not only differ from conventional processes by featuring a different type of catalyst but they constitute a new technology base ... 

As in the case of chemical processing, all enzyme reactors can be classified according to the degree of mixedness of the substrate and product solution they belong to only a few basic types. The different reactor types used in biocatalysis are depicted in Figure 5.5. 

Further advantages of biocatalysis over chemical catalysis include shorter synthesis routes and milder reaction conditions. Enzymatic reactions are not confined to in vivo systems - many enzymes are also available as isolated compounds which catalyze reactions in water and even in organic solvents [28]. Despite these advantages, the activity and stability of most wild-type enzymes do not meet the demands of industrial processes. Fortunately, modern protein engineering methods can be used to change enzyme properties and optimize desired characteristics. In Chapter 5 we will outline these optimization methods, including site-directed mutagenesis and directed evolution. 

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