Biocatalysis definition

One of the most actively investigated aspects of the biohydrolysis of carboxylic acid esters is enantioselectivity (for a definition of the various stereochemical terms used here, see [7], particularly its Sect. 1.5) for two reasons, one practical (preparation of pure enantiomers for various applications) and one fundamental (investigations on the structure and function of hydrolases). The synthetic and preparative aspects of enantioselective biocatalysis by hydrolases have been extensively investigated for biotechnology applications but are of only secondary interest in our context (e.g., [16-18], see Sect. 7.3.5). In contrast, the fundamental aspects of enantioselectivity in particular and of structure-metabolism relationships in general are central to our approach and are illustrated here with a number of selected examples. 

These case studies are an attempt to demonstrate the complexity of the commercialisation of biocatalytic (biotransformations/bioprocessing) processes, and to compare the technical and business factors that all contribute to the success or failure of particular biocatalysis-based industrial projects. This chapter is definitely not a straightforward review of the science involved, such information is mostly readily available from other pnblished sonrces. Instead, in each example some background information has been given, and then important technical and commercial factors that have influenced the snccess or futnre of the prodnct in the market place are highlighted. Examples are inclnded that ... 

Biocatalysis, A. S. Bommarius and B. R. Riebel, Wiley-VCH 2004, 611 pp., ISBN 3-527-30344-8. This is a comprehensive advanced textbook covering all aspects of biocatalysis. There are many good examples with references. It is a serious book, definitely not light reading, but one to have on the shelf if you are going to work in biocatalysis. 

Adsorption on a solid catalyst surface, complex formation in homogeneous catalysis with metallo-organic complexes and in biocatalysis with enzymes share the same principle, i.e. the total number of sites is constant. Therefore, the rate expressions for reactions on heterogeneous, homogeneous and biocatalysts have a similar form. The constant number of active sites results in rate expressions that differ from homogeneous gas phase kinetics. Partial pressures are usually used in rate expressions for gas-phase reactions, while concentrations are used when the reactions take place in the liquid phase. It appears that definitions and nomenclature of particular kinetics constants in the different sub-communities differ sometimes. In the following sections the expressions used by the different subdisciplines will be compared and their conceptual basis outlined. 

In biocatalysis /C2 is the rate measured when all enzyme molecules are complexed with reactant divided by the total concentration of enz)one present. This is the Turn-Over Number according to biochemists definition. Note that this differs from the Turn-Over Frequency as defined in heterogeneous catalysis where it is simply the rate normalised to the total number of surface sites present. In the latter case it is a function of the gas phase composition. 

The above presented definitions for the TON and TOP, however, vary slightly depending on the type of catalyst. In heterogeneous catalysis, for example, the TON and TOP are often defined per active site or per gram catalyst. In contrast, in biocatalysis, they are defined by the rate measured when all the enzyme molecules are complexed with a reactant, divided by the total enzyme concentration. Thus, when dealing with TON and TOP data it is important to provide the units in order to avoid misunderstandings. 

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