Applications of Enzyme Catalysis

Preparation of animal feed proteases, amylases, hemicellulases 

Laundry detergents proteases, cellulases, lipases, amylases 

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In several recent applications of enzyme catalysis, the snbstrates on which the enzymes act are not the kind of snbstrates that are natnral to the enzyme. However, enzyme catalysed synthesis of hexoses in the laboratory depends solely on enzymes acting on natural or near natnral snbstrates. The relevant enzymes are the aldolases (EC 4.1.2 aldehyde-lyases) since they catalyse an aldol type of C-C bond forming aldol addition reaction. The aldolases most commonly join two C-3 units, called donor and acceptor, and two new stereocentra are formed with great stereoselectivity. 

In considering the application of enzyme catalysis to DCC, we were encouraged by the thermodynamic resolution of a dynamic mixture of aldol products by Whitesides and co-workers through the use of a broad-specificity aldolase to lead to reversible formation of carbon-carbon bonds under mild conditions.35 For the current investigation36 we chose a related enzyme, N-acetylneuraminic acid aldolase (NANA aldolase, EC 4.1.3.3), which catalyzes the cleavage of N-acetylneuraminic acid (sialic acid, 27a) to A-acetylmannosamine (ManNAc, 28a), and sodium pyruvate 29 in the presence of excess sodium pyruvate, aldol products 27a-c are generated from... 

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. 

As a dominant technology in the chemicals industries, catalysis provides an important long-term commercial target for biotechnology. While enzymes represent the most efficient catalytic systems known, their impact on the chemicals industry relative to traditional catalysts is still small. Developments at the interface of biology and chemistry will be key to overcoming the major barriers to broad industrial application of enzyme catalysis. 

Even though there are so many advantages to using enzymes as substitutes for chemical catalysts, practical applications of enzyme catalysis are few and far between. This is largely due to their relatively poor stabilities and catalytic activities under the conditions that characterize industrial processes high temperatures, extremes of pH or non-aqueous solvents. Enzymes evolved for the survival benefit of an organism may not exhibit features essential for in vitro application (30). 

A recent application of enzyme catalysis (oxalyl chloride, 50 U aminoacylase E.C. 3.5.1.14, hexane, 4 days, 20 °C) for the synthesis of unsymmetrical diaryl ketones has been reported [949]. 

The chemical reaction catalyzed by triosephosphate isomerase (TIM) was the first application of the QM-MM method in CHARMM to the smdy of enzyme catalysis [26]. The study calculated an energy pathway for the reaction in the enzyme and decomposed the energetics into specific contributions from each of the residues of the enzyme. TIM catalyzes the interconversion of dihydroxyacetone phosphate (DHAP) and D-glyceraldehyde 3-phosphate (GAP) as part of the glycolytic pathway. Extensive experimental studies have been performed on TIM, and it has been proposed that Glu-165 acts as a base for deprotonation of DHAP and that His-95 acts as an acid to protonate the carbonyl oxygen of DHAP, forming an enediolate (see Fig. 3) [58]. 

Cherepanov, A.V. and DeVries, S. 2004. Microsecond freeze-hyperquenching development of a new ultrafast micro-mixing and sampling technology and application to enzyme catalysis. Biochimica et Biophysica Acta 1656 1-31. 

For some recent reviews on the use of enzymes in nonconventional media, see (a) Dreyer, S., Lembrecht, J., Schumacher, J. and Kragl, U., Enzyme catalysis in nonaqueous media past, present, and future in biocatalysis in the pharmaceutical and biotechnology industries, 2007, CRC Press, pp. 791-827 . (b) Torres, S. and Castro, G.R., Non-aqueous biocatalysis in homogeneous solvent systems. Food Technol. BiotechnoL, 2004, 42, 271-277 (c) Carrea, G. and Riva, S., Properties and synthetic applications of enzymes in organic solvent. Angew. Chem. Int. Ed., 2000, 39, 2226-2254. 

Lipase has been used in organic solvents to produce useful compounds. For example, Zark and Klibanov (8) reported wide applications of enzymes to esterification in preparing optically active alcohols and acids. Inada et al (9) synthesized polyethylene glycol-modified lipase, which was soluble in organic solvent and active for ester formation. These data reveal that lipases are very useful enzymes for the catalysis different types of reactions with rather wide substrate specificities. In this study, it was found that moditied lipase could also synthesize esters and various lipids in organic solvents. Chemically moditied lipases can help to solve today s problems in esteritication and hopefully make broader use of enzymatic reactions that are attractive to the industry. 

The chemistry of the metalloenzymes must be considered as a special case of enzymic catalysis since most active sites of enzymes are stereospecific for only one molecule or class of molecules and many do not involve metal ions in catalysis. Since the metal ion is absolutely essential for catalysis in the examples chosen for this review, the mechanisms undoubtedly involve the metal ion and a particular protein microenvironment or reactive group(s) as joint participants in the catalytic event. It is our belief that studies of catalysis by metalloenzymes will have as many, if not more, features characteristic of protein catalysis in general, in a fashion similar to metal ion catalysis, and these studies will be directly applicable to heterogeneous and homogeneous catalytic chemical systems where the metal ion carries most of the catalytic function. 

The solubilization phenomenon, which refers to the dissolution of normally insoluble or only slightly soluble compounds in water caused by the addition of surfactants, is one of the most striking effects encountered for surfactant systems. Solubilization is of considerable physico-chemical interst, such as in discussion of the structure and dynamics of micelles and of the mechanism of enzyme catalysis, and has numerous practical applications, such as in detergency, in pharmaceutical preparations and in micellar catalysis. In biology, solubilization phenomena are most significant, e.g., cholesterol solubilization in phospholipid bilayers and fat solubilization in fat digestion and transport. 

Another area of great importance is the emerging application of bio-catalysis using nature s catalysts such as enzymes to produce a growing number of pharmaceutical and agricultural products. This subject is outside the scope of this review so other sections of this Handbook (see chapter 31) should be consulted. 

Ultimately the distinction between biological and chemical catalysis may become less distinct as technologies for modified enzymes, enzyme mimetics, and chemoenzymatic catalysis advance. In the meantime, however, it is clear that further application of enzyme technology within industry will greatly benefit society in the twenty-first century. 

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