Organic enzyme selectivity

The term medium engineering , that is the possibility to affect enzyme selectivity simply by changing the solvent in which the reaction is carried out, was coined by Klibanov, who indicated it as an alternative or an integration to protein engineering [5aj. Indeed, several authors have confirmed that the enantio-, prochiral-, and even regioselectivity of enzymes can be influenced, sometimes very remarkably, by the nature of the organic solvent used. 

In the following text, examples of solvent effects on enzyme selectivity, referred either to systems based (i) on water-miscible organic cosolvents added to aqueous buffers or (ii) on organic media with low water activity, are discussed. 

The simplest way to prepare a biocatalyst for use in organic solvents and, at the same time, to adjust key parameters, such as pH, is its lyophilization or precipitation from aqueous solutions. These preparations, however, can undergo substrate diffusion limitations or prevent enzyme-substrate interaction because of protein-protein stacking. Enzyme lyophilization in the presence of lyoprotectants (polyethylene glycol, various sugars), ligands, and salts have often yielded preparations that are markedly more active than those obtained in the absence of additives [19]. Besides that, the addition of these ligands can also affect enzyme selectivity as follows. 

Hoch U, ScheUer G, Schmitt M, Schreier P, Adam W, Saha-MoUer CR (1995) Enzymes in synthetic organic chemistry selective oxidoreductions catalyzed by the metaUoenzymes lipoxygenase and peroxidase. In Werner H, Simdermeyer J (eds) Stereoselective reactions of metal-activated molecules, 2nd Symposium. Vieweg, Braimschweig, p 33 Adam W, Korb MN (1997) Tetrahedron Asymmetry 8 1131... 

Chemically modified-CDs have also proven useful as organic enzyme mimics (10). Modified CDs have catalyzed the de-esterification, hydrolysis, selective substitution, addition and isomerization of a variety of molecules (9). Advances in the chemical s3mthesis of CDs (11) and unusual "manno" CDs (12) promise novel new CD-like materials in the future. 

G. Carrea, G. Ottolina, and S. Riva, Role of solvents in the control of enzyme selectivity in organic media, Trends Biotechnol. 1995, 13, 63-70. 

EMP at http //wit.mcs.anl.gov/EMP/ is the resource site for summarized enzyme data that have been published in the literature. The site opens with the Simple query form (Figure 7.6). Enter the enzyme name into the name query box of Find an enzyme, select Common name, then enter the common organism name for In an organism or taxon, and enter tissue name in response to Extracted from. Clicking Submit Query returns an itemized summary of published enzyme data (data from one article may appear in more than one entries for different substrates) including concise assay and purification procedures, kinetic equations and kinetic parameters. 

The ruthenium-catalyzed reactions by their diversity, selectivity, and interest for the production of fine chemicals, especially during the last decade, show that molecular ruthenium catalysts are not only versatile but that they have now become unavoidable tools in organic synthesis [127]. They also appear to be complementary to organic, enzyme, or other metal catalysts as they have the power to generate original activation pathways for the combination of a variety of simple and complex molecules. 

There are only a few MCRs of type III known in preparative organic synthesis h l in living cells, however, the majority of bioorganic chemical compounds are formed by MCRs of type III. In these cases suitable enzymes selectively accelerate the required sequences of subreactions. 

Most enzymes present in the body play an essential biochemical role, but several of them also have an undesirable characteristic which requires selective suppression. Thus, the degrading effect of human leukocyte elastase on elastin (which provides elastic properties in several organs) requires selective inhibitors which are discussed in Chapter 2. 

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