Enzymatic catalysis selectivity

It is apparent that the use of enzymatic catalysis continues to grow Greater availabiUty of enzymes, development of new methodologies for thek utilization, investigation of enzymatic behavior in nonconventional environments, and the design and synthesis of new biocatalysts with altered selectivity and increased stabiUty are essential for the successhil development of this field. As more is learned about selectivity of enzymes toward unnatural substrates, the choice of an enzyme for a particular transformation will become easier to predict. It should simplify a search for an appropriate catalyst and help to estabhsh biocatalytic procedures as a usehil supplement to classical organic synthesis. 

Enzymes are proteins catalyzing all in vivo biological reactions. Enzymatic catalysis can also be utilized for in vitro reactions of not only natural substrates but some unnatural ones. Typical characteristics of enzyme catalysis are high catalytic activity, large rate acceleration of reactions under mild reaction conditions, high selectivities of substrates and reaction modes, and no formation of byproducts, in comparison with those of chemical catalysts. In the field of organic synthetic chemistry, enzymes have been powerful catalysts for stereo- and regioselective reactions to produce useful intermediates and end-products such as medicines and liquid crystals. ... 

Production of all naturally occurring polymers in vivo is catalyzed by enzymes. Polymerizations catalyzed by an enzyme ( enzymatic polymerizations ) have received much attention as new methodology [6-11], since in recent years structural variation of synthetic targets on polymers has begun to develop highly selective polymerizations for the increasing demands in the production of various functional polymers in material science. So far, in vitro syntheses of not only biopolymers but also non-natural synthetic polymers through enzymatic catalysis have been achieved [6-11]. 

Dordick, J.S. (July 1991) Enzymatic catalysis in organic media Fundamentals and selected applications. ASGSBBull. 4(2), 125-132. 

It can be seen then that heterogeneous catalysis may find an opportunity for replacing the enzymatic catalysis of disaccharides to its monosaccharides, and thereby provide industry with a more efficient and benign route. However, it is also clear that more selective catalysts are required. 

Recently, diphenylglycoluril-based host compounds have been used to construct catalysts that mimic certain aspects of enzymatic catalysis, e.g. rate enhancement and selectivity. The goal is to bring a binding site and a catalytic center in close... 

Selectivity is an intrinsic properly of enzymatic catalysis. [3] Following the nomenclature proposed by Cleland [24, 25], the pseudo second-order rate constant for the reaction of a substrate with an enzyme, kml/KM, is known as the specificity constant, ksp. [26] To express the relative rates of competing enzymatic reactions, involving any type of substrates, the ratio of the specificity constants appears to be the parameter of choice [3]. Since the authoritative proposition by Sih and coworkers [27], the ratio of specificity constants for the catalytic conversion of enantiomeric substrates, R and S, is commonly known as the enantiomeric ratio or E -value (Equation 1) ... 

Discuss the implications of Pauling s 1948 statement that Enzymes are molecules that are complementary in structure to the transition states of the reactions they catalyse. Include in your answer a discussion of the selectivity of enzymatic catalysis. 

Mimetic catalysis designs a real model (a mimic) which simulates objects and processes of enzymatic catalysis by their basic (but deficient) characteristics (selectivity, mildness of condition, active site action mechanism, etc.). Since only definite properties of the enzyme are simulated, it does not profess to a complete enzyme description, though optimal parameters by some properties may be approached. The mimetic model of enzyme helps in synthesizing suitable catalysts using inaccurate and sometimes ambiguous information. 

FIGURE 5.4 A schematic showing the qualitative difference between enzymatic and nonenzymatic catalysis. In enzymatic catalysis, the transition state of a specific pathway is stabilized. Typical nonenzymatic catalysis, such as protic or Lewis acid, results in increasing the energy of the starting material, making several pathways energetically accessible. This difference is the source of the selectivity found in enzymatic catalysis as well as the presence of by-products in nonenzymatic catalysis. 

In these two examples, the principle of transition-state stabilization as a source of enzymatic catalysis is successfully exploited for the selection of active mutants. Selection with a TSA appears to be able to enrich libraries in variants with high catalytic activity. 

B27, B32, K28, K32, M22, Rl). In addition to utilizing the sensitivity, specificity, and selectivity inherent in the enzymatic catalysis of reactions, the technique can be performed with a minimum amount of sample and sample workup, in a very short time. With the use of appropriate enzymes, it is possible to determine both the identity and purity of a substrate compound. 

Retey, J., 1990, Enzymatic-reaction selectivity by negative catalysis or how do enzymes deal with highly reactive intermediates. Angew. Chem. Inti. Ed. Engl. 29 3559361. 

---