Application Range of Biocatalysis

Therefore, biocatalysis offers great chances and advantages for successful applications also in cases where either the substrates or the products of the reaction are chemically labile. 

According to the EC-System of the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology IUBMB [2], the enzymes are classified in six main classes (Table l).To allow a refined classification, the main classes are subdivided into three orders of enzyme subclasses (EC X.a.b.c., e.g., EC 1.1.1.1 for alcohol dehydrogenase). The majority of the described enzymes belong to the EC classes 1,2 and 3. 

Very detailed information on all the 3400 EC-classified enzymes (organized in fact sheets) can be found in the excellent Enzyme Handbook [3] edited by GBF (Gesellschaft fiir Bio-technische Forschung in Braunschweig) in 17 Volumes, so far. The same information is also available in electronic form via BRENDA (Braunschweig Enzyme Databank). 

The state of the art is described in many excellent and comprehensive books [4-29] and general review articles [30-70], The reference list gives only the most prominent and best known reviews. Additional and highly recommendable information sources for the synthetic chemist are the Warwick Biotransformation Abstracts and the associated electronic database. Contact address H.G. Crout, Warwick Biotransformation Club Database, Organic Chemical Institute, University of Warwick, UK (service for members only). The two CD-ROMs Biotransformation (K. Kieslich and the Warwick Biotransformation Club) and BioCatalysis (H.L. Holland and B. Jones) are available from Chapman Hall (London, 1996). Practical examples for preparative biotransformations (with checked procedures) 

IUBMB enzyme class Reactions catalyzed / special requirements 

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Biocatalysis is normally performed in an aqueous environment, but can in many cases also be conducted in solvent mixtures, liquid-liquid two-phase systems, and even in pure organic solvents. This extends the traditional (natural) application range of biocatalysis to more lipophilic starting materials and opens up the way to new reactions. A relevant practical example is the use of esterases and lipases to catalyze esterifications in organic solvents such as vinyl acetate. 

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 ... 

The study of the ion transfer through artificial liquid membrane systems is important for the elucidation of the ion transfer through biological membranes. In this respect, the Interface between two inmiscible electrolyte solutions (ITIES) constitutes a biomimetic medium suitable for studying several fundamental processes, ranging from biocatalysis to cellular respiration of photosynthesis, and many others [18-22], The first studies of liquid/liquid interfaces (L/L) under the application of an external potential were carried out by Gavach et al. [23], laying the basis for the current electrochemical treatments of ITIES. 

The use of industrial enzymes for the synthesis of bulk and fine chemicals represents a somewhat specialized application for biocatalysts relative to their broader uses, as outlined above. Industrial biocatalysis is, however, becoming increasingly relevant within the chemical industry for the production of a wide range of materials (see Table 31.3).1,2,4-8 Broadly defined, a biocatalytic process involves the acceleration of a chemical reaction by a biologically derived catalyst. In practice, the biocatalysts concerned are invariably enzymes and are used in a variety of forms. These include whole cell preparations, crude protein extracts, enzyme mixtures, and highly purified enzymes, both soluble and immobilized. 

One of the inherent advantages of enzymes is the ability to discriminate between stereoisomers, often generating products with ena-tiomeric excesses (i.e., of over 98%). Judicious application of biocatalysis can also reduce the number of chemical steps needed to synthesize certain drugs, leading to hybrid chemoenzymatic processes with lower costs and less waste. The range of enzymes used in the synthesis of chiral intermediates has expanded beyond esterases and acylases and... 

Biocatalysis covers a broad range of scientific and technical disciplines, which are geared to develop biocatalysts and biocatalytic processes for practical purposes. The natural pool of biocatalysts is extremely diverse and includes whole cells of microbial, plant or animal origin, as well as cell-free extracts and enz3rmes derived from these sources. The wide range of catalytic power offered by nature remains, however, largely imexplored. Currently, only a very small fraction of the known biocatalysts are actually being applied on a commercial scale. For example, of the approximately 4,000 known enzymes, about 400 are available commercially, but only about 40 are actually used for industrial applications. 

A range of excellent and recent reviews can be found, in which the use of enzymes within specific branches or disciplines of organic chemistry is highlighted. These include biocatalysis in carbohydrate chemistry [39], polymer chemistry [40] and for protecting group manipulations [41]. The present chapter is focused on immobilized enzymes. Hence, as an appetizer, a few selected applications with Novozym 435 are presented below, followed by a short subsection discussing industrial-scale applications of immobilized enzymes. 

Since the late 1960s immobilized biocatalysts have been extensively studied and used for the industrial production of important intermediates and products such as amino acids, sugars, lipids, acids, and pharmaceuticals [ 1-3]. A recent OECD report not only states that biocatalysts can and should be used in a wide range of industrial applications, but also identifies a need for reusable systems [4]. Improving the robustness of biocatalysts was also an important topic of a 1999 workshop of 50 leading scientific and industry experts in biocatalysis [5]. 

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