Enzyme large-scale application

Also illustrated in Figure 6.17 there is another important antibiotic, amoxicillin. Both amoxicillin and ampiciilin can be made enzymatically or chemically. Although enzymes are available that can be applied very well for the conversion of 6-APA into a variety of semi-synthetic penicillins, economic reasons are still impeding large scale applications. 

At present the hydrogenase is very expensive and commercially unavailable enzyme for large scale application. There are three approaches to design rather cheap hydrogenactivating catalyst ... 

Since the large-scale application of immobilized enzymes in the 1960s, substantial research efforts have aimed to optimize the structure of carrier materials for better catalytic efficiency. To date, nanoscale materials may provide the upper limits in... 

The thermodynamics of these reaction systems have been investigated, resulting in methods to predict the direction of a typical reaction a priori. Furthermore, studies on kinetics, enzyme concentration, pH/temperature effects, mixing, and solvent selection have opened up new perspectives for the understanding, modeling, optimization, and possible large-scale application of such a strategy. 

To overcome problems of poor acceptor substrate acceptance, high concentrations of aldehyde substrates are required to obtain synthetically useful product yields. Unfortunately, DERA shows rather poor resistance to such high aldehyde concentrations, especially toward CIAA, resulting in rapid, irreversible inactivation of the enzyme. Therefore, the organic synthesis of (3R,5S)-6-chloro-2,4,6-trideoxy-hexapyranoside 1 requires very high amounts of DERA. Thus, despite the synthetic usefulness of DERA to produce chiral intermediates for statin side chains, the large-scale application is seriously hampered by its poor stability at industrially relevant aldehyde concentrations. The production capacity for such 2,4,6-trideoxy-hexoses of wild-type E. coli DERA is rather low [15]. 

Finally, for an overall perspective on catalysis of all types, here are a few words about biochemical catalysts, namely, enzymes. In terms of activity, selectivity, and scope, enzymes score very high. A large number of reactions are catalyzed very efficiently, and the selectivity is high. For chiral products enzymes routinely give 100% enantioselectivity. However, large-scale application of enzyme catalysis in the near future is unlikely for many reasons. Isolation of a reasonable quantity of pure enzyme is often very difficult and expensive. Most enzymes are fragile and have poor thermal stability. Separation of the enzyme after the reaction is also a difficult problem. However, in the near future, catalytic processes based on thermostable enzymes may be adopted for selected products. 

Immobilization can be achieved by adsorption or covalent fixation of the biocatalyst to a solid support (e.g. surface-modified polymer or glass beads), by entrapment or by encapsulation in gel beads (e.g., agarose, polyacrylamide, alginate, etc.). Hundreds of immobilization methods have been described and reviewed in the literature [83-89], but only a limited set of methods has found real technical applications. The first large-scale applications of immobilized enzymes were established for the enantioseparation of D- and L-amino acids by Chib-ata, Tosa and co-workers at Tanabe Seiyaku Company. The Japanese achievements in the large-scale application of immobilized systems are very well documented in an excellent multi-author publication edited by Tanaka, Tosa and Kobayashi [90] (see also section 7). Some enzyme suppliers sell important industrial enzymes not only in the free form (solution or powder) but also immobilized on solid supports. 

Many of today s large-scale applications use immobilized enzymes. In particular, the Japanese industry has for a long time pioneered this sector of biotechnology. In the multi-author publication edited by Tanaka, Tosa and Kobayashi [90] and in a more recent review [89], a number of well-established continuous production processes with immobilized biocatalysts are described in detail (for a selection, see below). Complementary information on some of these Japanese bioprocesses as well as additional case studies for other bioprocesses has been compiled by Cheetham [170],... 

However, the use of these ionic and redox polymers was rather limited to applications, such as molecular electronic devices, or sensors and biosensors (using immobilized enzymes), where the need for fast electrochemical reactions was not essential, because of the limitation of the reaction rate by a slow charge transport process inside the polymer (see Section 2). This excludes large-scale applications, as in fuel cells or in organic electrosynthesis. 

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