Catalysis enzyme-catalyzed

Similarly to homogeneous and heterogeneous catalysis, enzyme catalyzed reactions occur at a specific active site, which is dependent on the arrangement of functional groups. 

Enzyme catalysis requires that Kj- < Kg. According to transition-state theory (see references at end of chapter), the rate constants for the enzyme-catalyzed k ) and uncatalyzed k reactions can be related to Kg and K by ... 

If the enzyme-catalyzed reaction is to be faster than the uncatalyzed case, the acceptor group on the enzyme must be a better attacking group than Y and a better leaving group than X. Note that most enzymes that carry out covalent catalysis have ping-pong kinetic mechanisms. 

Molecular characteristics of luciferase. A molecule of the luciferase of G. polyedra comprises three homologous domains (Li et al., 1997 Li and Hastings, 1998). The full-length luciferase (135 kDa) and each of the individual domains are most active at pH 6.3, and they show very little activity at pH 8.0. Morishita et al. (2002) prepared a recombinant Pyrocystis lunula luciferase consisting of mainly the third domain. This recombinant enzyme catalyzed the light emission of luciferin (luminescence A.max 474 nm) and the enzyme was active at pH 8.0. The recombinant enzyme of the third domain of G. polyedra luciferase was crystallized and its X-ray structure was determined (Schultz et al., 2005). A -barrel pocket putatively for substrate binding and catalysis was identified in the structure, and... 

The interest and success of the enzyme-catalyzed reactions in this kind of media is due to several advantages such as (i) solubilization of hydrophobic substrates (ii) ease of recovery of some products (iii) catalysis of reactions that are unfavorable in water (e.g. reversal of hydrolysis reactions in favor of synthesis) (iv) ease of recovery of insoluble biocatalysts (v) increased biocatalyst thermostability (vi) suppression of water-induced side reactions. Furthermore, as already said, enzyme selectivity can be markedly influenced, and even reversed, by the solvent. 

Hence, l/K only approximates l/K under conditions where the association and dissociation of the ES complex is rapid relative to the rate-limiting step in catalysis. For the many enzyme-catalyzed reactions for which + kj is not approximately equal to k j, IIK will underestimate IIK,. 

E---S + R E---P->E + P The enzyme is regenerated at the end of this sequence, making it available to bind another substrate molecule. Note that the steps in this enzyme-catalyzed biochemical mechanism are similar to the steps in chemical heterogeneous catalysis binding with bond weakening, reaction at the bound site, and release of products. 

In the recent decades, an enzyme-catalyzed polymerization ( enzymatic polymerization ) has been of increasing importance as a new trend in macro-molecular science. Enzyme catalysis has provided new synthetic strategy for useful polymers, most of which are difficult to produce by conventional chemical... 

In this chapter we have seen that enzymatic catalysis is initiated by the reversible interactions of a substrate molecule with the active site of the enzyme to form a non-covalent binary complex. The chemical transformation of the substrate to the product molecule occurs within the context of the enzyme active site subsequent to initial complex formation. We saw that the enormous rate enhancements for enzyme-catalyzed reactions are the result of specific mechanisms that enzymes use to achieve large reductions in the energy of activation associated with attainment of the reaction transition state structure. Stabilization of the reaction transition state in the context of the enzymatic reaction is the key contributor to both enzymatic rate enhancement and substrate specificity. We described several chemical strategies by which enzymes achieve this transition state stabilization. We also saw in this chapter that enzyme reactions are most commonly studied by following the kinetics of these reactions under steady state conditions. We defined three kinetic constants—kai KM, and kcJKM—that can be used to define the efficiency of enzymatic catalysis, and each reports on different portions of the enzymatic reaction pathway. Perturbations... 

Rasor, J.P. and Voss, E. (2001) Enzyme-catalyzed processes in pharmaceutical industry. Applied Catalysis A-General, 221 (1-2), 145-158. 

Enzyme catalysis. Enzymes are proteins, polymers of amino acids, which catalyze reactions in living organisms-biochemical and biological reactions. The systems involved may be colloidal-that is, between homogeneous and heterogeneous. Some enzymes are very specific in catalyzing a particular reaction (e.g., the enzyme sucrase catalyzes the inversion of sucrose). Enzyme catalysis is usually molecular catalysis. Since enzyme catalysis is involved in many biochemical reactions, we treat it separately in Chapter 10. 

This final chapter summarizes the enzyme-catalyzed asymmetric reactions and introduces some new developments in the area of asymmetric synthesis. Among the new developments, cooperative asymmetric catalysis is an important theme because it is commonly observed in enzymatic reactions. Understanding cooperative asymmetric catalysis not only makes it possible to design more enan-tioselective asymmetric synthesis reactions but also helps us to understand how mother nature contributes to the world. 

The use of the symbol E in 5.1 for the environment had a double objective. It stands there for general environments, and it also stands for the enzyme considered as a very specific environment to the chemical interconversion step [102, 172], In the theory discussed above catalysis is produced if the energy levels of the quantum precursor and successor states are shifted below the energy value corresponding to the same species in a reference surrounding medium. Both the catalytic environment E and the substrates S are molded into complementary surface states to form the complex between the active precursor complex Si and the enzyme structure adapted to it E-Si. In enzyme catalyzed reactions the special productive binding has been confussed with the possible mechanisms to attain it lock-key represents a static view while the induced fit concept... 

Enzyme business, growth in, 10 311 Enzyme catalysis, 20 830 dendrimers in, 26 806 Enzyme catalysts, 16 395 Enzyme-catalyzed reactions,... 

Because practically all aromatic organic pollutants that release phenols or anilines in the course of their degradation could bind HS through enzymatic catalysis, methods employing enzyme-catalyzed polymerization reactions minimizing their presence by partial removal in aquatic and terrestrial environments might be utilized in pollution control. This can have a remarkable effect in environmental engineering practice. 

Abstract This chapter introduces the basic principles used in applying isotope effects to studies of the kinetics and mechanisms of enzyme catalyzed reactions. Following the introduction of algebraic equations typically used for kinetic analysis of enzyme reactions and a brief discussion of aqueous solvent isotope effects (because enzyme reactions universally occur in aqueous solutions), practical examples illustrating methods and techniques for studying enzyme isotope effects are presented. Finally, computer modeling of enzyme catalysis is briefly discussed. 

Although conformational changes are essential features of proteins, the conformational basis of protein activity is not yet understood at the molecular and atomic levels. It is generally assumed that the mechanism of enzyme-catalyzed reactions would he defined if all the intermediates and transition states between the initial and final stages, as well as the rate constants, could be characterized. But in spite of constant progress in such characterization, most enzymatic mechanisms are not understood in terms of physical organic chemistry and enzyme activity is still regarded as a miracle as compared to classical catalysis. 

As shown in Table 12,H202 and fBuOOH have been used frequently as oxygen donors in peroxidase-catalyzed sulfoxidations. Other achiral oxidants, e.g. iodo-sobenzene and peracids, are not accepted by enzymes and, therefore, only racemic sulfoxides were found (c.f. entries 34-36). Interestingly, racemic hydroperoxides oxidize sulfides to sulfoxides enantioselectively under CPO catalysis [68]. In this reaction, not only the sulfoxides but also the hydroperoxide and the corresponding alcohol were produced in optically active form by enzyme-catalyzed kinetic resolution (cf. Eq. 3 and Table 3 in Sect. 3.1). 

Life is sustained by a complex web of chemical reactions. Catalysts, molecules that accelerate the rate of a chemical reaction but that are unchanged by the overall reaction, are essential for life as most reactions would otherwise occur far too slowly. Indeed, it can be argued that the evolution of life is essentially the story of the evolution of catalysis. In nature, most catalysts are proteins and these catalytic proteins, or enzymes, are one of the most remarkable classes of molecules to have been generated during evolution. Enzymes catalyze an enormous range of different reactions and their performances typically far exceed those of man-made catalysts. They can accelerate reactions by anything up to 10 -fold relative to the uncatalyzed reaction, enabling reactions that would otherwise have half-lives of tens of millions of years to be performed in milliseconds. 

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