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Catalytic efficiency, of enzymes

A final important area is the calculation of free energies with quantum mechanical models [72] or hybrid quanmm mechanics/molecular mechanics models (QM/MM) [9]. Such models are being used to simulate enzymatic reactions and calculate activation free energies, providing unique insights into the catalytic efficiency of enzymes. They are reviewed elsewhere in this volume (see Chapter 11). [Pg.196]

EIA systems take advantage of the extreme specificity and affinity with which antibodies bind antigens which stimulated their initial production, coupled to the catalytic efficiency of enzymes, which facilitates signal amplification as well as straightforward detection and quantification. In most such systems, the antibody is immobilized on the internal walls of the wells in a multi-well microtitre plate, which therefore serves as collection of reaction mini-test tubes. [Pg.177]

For the hydrolysis of phosphate esters under mild conditions, metal ions and metal complexes are the most efficient nonenzymatic reagents currently available. However, they do not reach the catalytic efficiency of enzymes, and higher reactivities are desirable in view of applications. To mimic enzymatic dinuclear sites is a strategy to generate more efficient artificial phosphoesterases. [Pg.212]

When an enzyme is mixed with a large excess of substrate (which is generally the case due to the high catalytic efficiency of enzymes), there is an initial period, the pre-steady state period, during which the concentrations of enzyme bound intermediates build up to their steady state levels. Once the intermediates reach their steady state concentrations (and this is generally achieved after milliseconds) the reaction rate changes only slowly with time. [Pg.157]

For a better understanding of the enzyme catalysis in nature, experimental and theoretical studies characterize the free energy profiles and catalytic efficiencies of enzymes under different conditions, which may define the performance of an enzyme in maintaining a constant flux or a constant pool concentration of the product, working under irreversible or reversible conditions etc. (Albery and Knowles, 1976 Stackhouse et al., 1985 Pettersson, 1992 Somogyi, Welch and Damjanovich, 1984). Only a few enzyme reactions have been analyzed in detail and further experimental investigations are necessary to characterize the enzymes, to draw general conclusions, and to deduce how much their evolution approximated the requirements for optimal catalysis . [Pg.316]

Catalytic antibodies generally do not approach the catalytic efficiency of enzymes, but medical and industrial uses for them are nevertheless emerging. For example, catalytic antibodies designed to degrade cocaine are being investigated as a potential aid in the treatment of cocaine addiction. [Pg.221]

The active site is not a passive receptacle for binding the substrate, but rather is a complex molecular machine employing a diversity of chemical mechanisms to facilitate the conversion of substrate to product. A number of factors are responsible for the catalytic efficiency of enzymes, including the following ... [Pg.55]

There has been intensive recent discussion, summarized elsewhere in this Handbook, about the potential contribution of strong hydrogen bonding to the catalytic efficiency of enzymes. A key question is conveniently summarized by... [Pg.1009]

There have been extensive discussions in the literature regarding maximization of the catalytic efficiency of enzymes and the value of their internal equilibrium constants is the equilibrium constant between substrates and products of the enzyme when all are bound productively) (98-102). For example, the value of A int is near unity for both liver alcohol dehydrogenase (78) and lactate dehydrogenase (103) when measured with their natural substrates. The ability of these same enzymes to function with alternative substrates with widely differing external equilibrium constants raises important questions regarding the relationships of the internal thermodynamics of such reactions. [Pg.486]

Figure 25 The middle layer of the model enzyme used by Bagdassarian and coworkers to examine the role of vibrations in promotion of catalysis. C is the catalytic subunit, and S the substrate. Molecular dynamics simulations were used to assess the catalytic efficiency of enzymes that varied in the number of flexible and stiff linkages between neighboring subunits in the white box. P (phantom) and N (neutral) subunits were not varied during the simulation. Reproduced with permission from G. S. B. Williams A. M. Hossain S. Shang D. E. Kranbuehl C. K. Bagdassarian, J. Theor. Comput. Figure 25 The middle layer of the model enzyme used by Bagdassarian and coworkers to examine the role of vibrations in promotion of catalysis. C is the catalytic subunit, and S the substrate. Molecular dynamics simulations were used to assess the catalytic efficiency of enzymes that varied in the number of flexible and stiff linkages between neighboring subunits in the white box. P (phantom) and N (neutral) subunits were not varied during the simulation. Reproduced with permission from G. S. B. Williams A. M. Hossain S. Shang D. E. Kranbuehl C. K. Bagdassarian, J. Theor. Comput.
Metal ion cofactors have varied roles to enhance the catalytic efficiency of enzymes in hydrolytic reactions, including facilitate substrate binding (water and organic substrate), gathering/template effects, function as an electrostatic catalyst (carbonyl polarization and transition state stabilization), function as a Lewis acid to lower the pA a of metal-water and stabilize the formation of the leaving group. Although their properties make several... [Pg.575]

Storm and Koshland followed by Milstien and Cohen have presented chemical evidence suggesting that orbital directional characteristics are a dominant and possible major cause of the catalytic efficiency of enzymes. [Pg.250]

Enzymes do have their disadvantages. Their solvent incompatibility and instability restrict their industrial use. However, researchers strive to find means to overcome such drawbacks to make use of the catalytic efficiency of enzymes. Aims Biologies (1997) has developed cross-linked enzyme crystals (CLECs) to increase the versatility of enzymes in organic reactions. CLECs exhibit a high level of stability in extreme conditions of temperature and pH and in exposure to both aqueous and organic solvents. The synthesis of the antibiotic cephalexin was carried out using CLECs (see Fig. 3.21). The N-protection step of methyl phenyl glycinate in the classical synthesis was eliminated. [Pg.64]

The catalytic efficiency of enzymes is a subject of great fascination, particularly when crystallographic structures are available and a great deal is known about the physical organic chemistry of the enzymatic mechanism. In this regard, the most studied enzyme of a group of enzymes called serine proteases is a-chymotrypsin. The term serine protease derives from the fact that this class of enzymes contain at their active site a serine hydroxyl group which exhibits unusual reactivity toward the irreversible inhibitor diiso-propylphosphorofluoridate (DFP). [Pg.208]

Charge and proton relay through hydrogen bonds have been proposed to contribute to the catalytic efficiency of enzymes, and in this sense reversed micelles provide an appropriate model to delineate the importance of such factors at the enzyme active site. Micellar surfaces also provide a convenient means for the reduction in dimensionality, an important factor in enhancing reaction rates. They also serve as good models to demonstrate the feasibility of ultrafast proton transfer when the reactants are localized in a suitable environment such as membrane surfaces and other complex biomacromolecules. [Pg.277]

The reaction is regioselective, producing / ara-phenols from monosubstituted benzene derivatives. Furthermore, alkylarenes with reactive side-chain sp C-H bonds could be chemoselectively hydroxylated without significant formation of side-chain oxygenated products. Kinetic and mechanistic models of the oxidation of phenol with HP, catalysed by a new macrocyclic cobalt(II) complex, have been proposed. The catalytic system displayed high catalytic activity and the catalytic character of a metalloenzyme, although it did not attain the catalytic efficiency of enzymes. [Pg.117]


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See also in sourсe #XX -- [ Pg.325 , Pg.328 ]




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