Enzymes as biocatalysts

In some cases it is more attractive to use whole microbial cells, rather than isolated enzymes, as biocatalysts. This is the case in many oxidative biotransformations where cofactor regeneration is required and/or the enzyme has low stability outside the cell. By performing the reaction as a fermentation, i.e. with growing microbial cells, the cofactor is continuously regenerated from the energy source, e.g. glucose. 

Burton SG. 2003. Oxidizing enzymes as biocatalysts. Trends Biotechnol 21(12) 543—549. 

The use of enzymes as biocatalysts for the synthesis of water-soluble conducting polymers is simple, environmentally benign, and gives yields of over 90% due to the high efficiency of the enzyme catalyst. Since the use of an enzyme solution does not allow the recovery and reuse of the expensive enzyme, well-established strategies of enzyme immobilization onto solid supports have been applied to HRP [22-30]. A recent work reported an alternative method that allows the recycle and reuse of HRP in the biocatalytic synthesis of ICPs. The method is based on the use of a biphasic catalytic system in which the enzyme is encapsulated by simple solubilization into an IL. The main strategy consisted of encapsulating the HRP in room-temperature IPs insoluble in water, and the other components of the reaction... 

Yair S, Ofer B et al (2008) Organophosphate degrading microorganisms and enzymes as biocatalysts in environmental and personal decontamination applications. Crit Rev Biotechnol 28(4) 265-275... 

Describe in your own words the advantages and disadvantages of using whole cells compared to isolated enzymes as biocatalysts, with respect to catalyst immobilization, catalyst recovery, ease of use, and product selectivity and purification. 

Although the interest of scientists in peroxidase enzymes has increased tremendously during the past decades, the application of these enzymes as biocatalysts in industrial processes is still negligible. Often the low activity and the fragile nature of these enzymes make their use challenging and sometimes results in poor productivities. Different aspects including heme deactivation (Chap. 12), redox potential modulation (Chap. 4), protein denaturation, and substrate availability have to be dealt with. 

In the enzymatic degumming process, part of the hydratable phosphatides is enzymatically modified by removing the fatty acid on the C-2 position of the glycerol, using a phospholipase A2 enzyme as biocatalyst. These modified phosphatides facilitate the removal of the remaining NHP. Table 4.10 shows the results of an enzymatic degumming... 

Enzymes as biocatalysts have been developed for aqueous reaction systems. Application of enzymes in the presence of organic solvents is of interest to organic chemists because substrates may not be sufficiently soluble in water, or the equilibrium of the desired reaction may be unfavorable in aqueous solution. The following general approaches are used ... 

Combined use of microbial enzymes as biocatalysts with chemical synthesis has its origin in the steroid transformation developed in the USA in the early 1950s. Arima and his group [11] invented a unique microbial conversion process, in which the aliphatic side-chain of cholesterol was cleaved to produce a steroid core as a starting material for chemical synthesis of steroid hormones. Yamada et al. discovered the reverse reaction of the pyridoxal-containing L-amino acid lyases and applied them to synthesize L-tryptophan and l-DOPA [12] from pyruvate, ammonia and corresponding aromatic compounds. Since these early achievements, a variety of unique processes with newly screened microbial enzymes as biocatalysts have been invented. 

Since many enzymes have capacities to catalyze reactions with even unnatural substrates and to produce unnatural compounds, hybrid use of enzymes as biocatalysts with chemical synthesis can realize processes to produce useful substances with higher flexibility than processes with growing cells. Discovery of novel microbial enzymes with required specificity by screening is a key to the establishment of such a hybrid processes. Many successful achievements in Japan are observed in this unique field of biotechnology. Application of nitrile hydratase to production of acrylonitriles has proved that biocatalysts can be applied to production of commodity chemicals beyond the presumed limitation of fine chemicals. Discovery of the enzymatic reactions to produce trehalose from starch is an example that reveals the possibility of microbial screening or what remains undiscovered in the microbial world. The importance of developing new application is also crucial in this field as shown in the case of transglutaminase and alkaline cellulase. 

A growing interest in the use of purified enzymes as biocatalysts in laboratory scale and industrial applications is being developed as an alternative to more traditional approaches, generally based on fermentation processes. 

The use of enzymes as biocatalysts can therefore be of extreme interest for individual applications mainly for the advantages it implies in terms of energy consumption, safety, pollution prevention and materials preservation. 

Researchers in both industry and academia have employed immobilized enzymes as biocatalysts. Immobilization usually involves attaching enzymes to solid supports and packing the supports in a tube through which liquid flows. One application has involved conversion of the lactose in dairy fluids to glucose and galactose, which would permit conversion of the whey produced in cheese manufacture to useful by-products. By averaging over the void spaces between solid particles and the particles themselves, one can obtain an effective rate expression per unit volume of the bed of biocatalyst. The rate expression is... 

Enzymes produced by microorganisms such as fungi or bacteria have been used for years in batch fermentation plants for the production of pharmaceuticals, beverages, foods, etc. The availability of almost pure enzymes enables one to carry out specific reactions under mild conditions. Side-product formation can also be limited and the synthesis of chemically active compounds, which would otherwise require extremely long reaction times, can be performed with low yields. The use of enzymes as biocatalysts can therefore be of extreme interest for individual applications, mainly for the advantages it grants in terms of energy consumption, safety, pollution prevention and materials preservation. 

The current applications could be improved further still, considering the potential uses of enzymes as biocatalysts. With research, more specific biocatalysts and more efficient immobilization could increase productivity, while avoiding enzyme release or deactivation. 

J.-M. Vatele, Lipid Synthesis and Manufacture (ed. F.D. Gunstone) Shield Academic Press, Sheffield (1999) pp.1-45. F.D. Gunstone, Enzymes as biocatalysts in the modification of natural lipids, J. Sci. Fd. Agric., 1999, 79, 1535-1549. 

M., and Syldatk, C. (2001) Hydan-toinases and related enzymes as biocatalysts for the synthesis of unnatural chiral amino acids. Curr. Opin. Biotechnd., 12 (6), 559 563. 

Enzymes as biocatalysts are also examined dne to their non-toxic, natural catalysts and therefore, are superior candidates for ROP of lactides. 

In nature, a huge repertoire of chemical transformations is catalyzed by many thousands of enzymes. Its precise 3D architecture allows each enzyme to exhibit a remarkable specificity for the conversion of a particular set of substrates. The introduction of these enzymes as biocatalysts in the industrial production of fine chemicals probably represents the uppermost innovation in the enzyme field in recent years. Since a company produces in-house many of the biocatalysts used within industrial processes (i.e., production for captive use or captive consumption), the information on the actual scale and commercial impact of many of these biocatalytic processes is often limited. Nevertheless, from the scarce publications on industrial use of biocatalysts, it can be concluded that numerous energy intensive chemical processes involving a high output of pollutants have now been replaced by environmentally friendly enzymatic processes (Schmid et al. 2001). 

Enzymes as Biocatalysts for Lipid-based Bioproducts Processing 345... 

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