Biocatalysis with Enzymes

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. 

Zhou Z, Hartmann M (2012) Recent progress in biocatalysis with enzymes immobilized on mesoporous hosts. Top Catal 55 1081-1100... 

Recently, recombinant biocatalysts obtained using Escherichia coli cells were designed for this process. The overexpression of all enzymes required for the process, namely, hydantoinase, carbamoylase, and hydantoin racemase from Arthrobacter sp. DSM 9771 was achieved. These cells were used for production of a-amino acids at the concentration of above 50 g 1 dry cell weight [37]. This is an excellent example presenting the power of biocatalysis with respect to classical catalysis, since a simultaneous use of three different biocatalysts originated from one microorganism can be easily achieved. 

An auspicious new strategy, in order to perform biocatalysis with hydrophobic substrates in w/o-microemulsion, is the usage of whole cells instead of purified enzymes [3,124,141]. There exist only a few surfactant-oil systems, in which whole cells are stable and suitable for a segmentation. Mainly the biodegradable surfactant based on sorbitan (Tween and Span) seems to be well suited for the solubilisation of whole cells in organic reaction media [142,143]. 

As well as demonstrating that solid/gas biocatalysis was possible with enzymes that usually act on liquid substrates, this system (compared to other non-conven-tional methods developed for overcoming problems in enzymatic catalysis such as substrate or product solubility or to permit modification of thermodynamic constraints) allows very precise control and independent variation of the thermodynamic activity of any substrate or other added component in the gaseous phase. 

The renaissance of biocatalysis, supported by the advent of recombinant DNA, is only about 20 years old. Recently several publications have appeared which deal specifically with the attitudes listed above (Rozzell, 1999 Bommarius, 2001 Rasor, 2001). Most of the points above can either be refuted or they can be levied against any novel catalytic technology the situation with some competing technologies such as chiral homogeneous catalysts is similar to that with enzymes (Chapters 18 and 20). 

Alcalde, M., Ferrer, M., Plon, F.J., and BaUesteros, A. 2006. Environmental biocatalysis From remediation with enzymes to novel green processes. TRENDS in Biotechnology, 24 281-7. 

If you have reached this point in the chapter with the feeling that enzymes are all very well for the experts but that you are unlikely ever to use one, then this section is for you. Immobilized enzymes are now freely available from several companies and pharmaceutical companies use them on a large scale almost as a matter of routine. There are still problems of course and most asymmetric synthesis is not done with enzymes. In this section we set out to convince you that enzymes are practical reagents in organic solvents as well as in water and that practical minded chemists use them. An excellent review may convince you more.49 Recently a whole issue of the journal Organic Process Research and Development (2002, 6, issue 4, 420 ff.) was devoted to biocatalysis and the introductory article50 makes the point too. 

Enzyme (and nucleic acid) immobilization This application of NPs is the one that is discussed in the present chapter. Various types of enzymes can be immobilized onto NPs [176]. Functionalization of NPs with co-factors (as NAD+) facilitates the biocatalysis from enzymes that need the presence of a cofactor (as lactate dehydrogenase or glucose oxidase) [188]. 

A great deal of attention has been given to co-drying additives with enzymes for low-water biocatalysis. Large improvements in rate as well as alterations in selectivity... 

Biomaterials constitute an equally exciting field of research that finds numerous applications in medical and industrial areas 3,4), In fact, much commonality is found in biomaterial and biocatalytic research. For example, many researchers in biomaterials work with enzymes, and, often, investigators in biocatalysis are producing natural polymers or polymers that are closely related but are are modified by chemical or enzymatic methods to improve their physical properties. 

Schultz C, Groeger H, Dinkel C, Drauz K, Waldmann H (2002) Special catalysts and processes biocatalysis and enzyme-analogous processes. In CornUs B, Herrmann WA (eds) Applied homogeneous catalysis with organometaUic compounds, 2nd edn. WUey-VCH,Weinheim,p 872... 

Alcalde M, Fenera M, Plou FJ et al. (2006) Environmental biocatalysis from remediation with enzymes to novel green processes. TIBTECH 24(6) 281-287 Alexeeva M, Carr R, Turner NJ (2003) Directed evolution of enzymes new biocateilysts for asymmetric synthesis Oig Biomol Chem 1 4133 137 Allen G, Lowe G (1973) Investigation of the active site of papain with fluorescent probes. Biochem J 133 679-686... 

The application of aqueous / supercritical biphasic media is not restricted to metal complex catalysis but has proven effective also for enzymatic and whole-cell biocatalysis [36]. In general, water plays an important role in coimection with biocatalysis. If water is completely absent, enzymes are often not catalytically active under supercritical conditions [37]. In the literature many examples of biocatalysis with supercritical fluids containing various amounts of water are known and a detailed account of this field is outside the scope of the present discussion. One example to highlight the use of a true biphasic system is the carboxylation of pyrrole... 

Adlercreutz P (2000) Eundamentals of biocatalysis in neat organic solvents. In Carrea G, Riva S (eds) Organic Synthesis with Enzymes in Non-aqueous Media. Wiley-VCH, Weinheim, p 3... 

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