Mechanisms of enzyme reactions

The kinetics of enzyme reactions were first studied by the German chemists Leonor Michaelis and Maud Menten in the early part of the twentieth century. They found that, when the concentration of substrate is low, the rate of an enzyme-catalyzed reaction increases with the concentration of the substrate, as shown in the plot in Fig. 13.41. However, when the concentration of substrate is high, the reaction rate depends only on the concentration of the enzyme. In the Michaelis-Menten mechanism of enzyme reaction, the enzyme, E, and substrate, S, reach a rapid preequilibrium with the bound enzyme-substrate complex, ES ... 

Analytic solution of the Michaelis-Menten kinetic equation The simplest mechanism of enzyme reactions is of the form... 

Example 5.4A Detailed model of the fumarase reaction The basic mechanism of enzyme reactions is... 

Product inhibition is another example of such an inhibition mechanism of enzyme reactions, and is due to a structural similarity between the substrate and the product. The mechanism of competitive inhibition in a unimolecular irreversible reaction is considered as follows ... 

Principle of optimum motion and mechanisms of enzymes reactions... 

In studies of catalase, much effort has been directed toward a determination of whether or not hydrogen peroxide could be dissociated from the enzyme-substrate intermediates of catalases and peroxidases. It should be pointed out that catalase, as contrasted with cytochrome oxidase, has been studied only at room temperature, and if any lesson is to be learned from the study of cytochrome oxidase 150), it is that the complexes are most likely to be identified at low temperatures, as precursors of the compounds. In this sense, they are of first importance and not to be ignored in our understanding of the mechanism of enzymic reactions. 

In a few cases, theoretical calculations of transition state and intermediate energies and geometries provide confirmation of experimental studies of the mechanism of enzyme reactions and suggest directions for further study. One of these is the hydration of carbon dioxide catalyzed by carbonic anhydrase, a zinc enzyme. Below pH 7, the uncatalyzed reaction HC03 + H2O + CO2 is favored. Above pH 7, the reaction is... 

A most promising approach to the simulation of enzyme-catalysed reactions is through methods which combine a quantum chemical description of the groups directly involved in the reaction, to calculate the electronic structure of the reacting system, with a simpler molecular mechanics treatment of the enzyme and the environment [17-19,41]. These are described as quantum mechanical/molecular mechanical methods, QM/MM for short. Interest in QM/MM methods has grown rapidly in recent years, and it is now clear that they can provide biochemically useful and relevant insight into the mechanisms of enzymic reactions [18,19,42,43]. These methods, and their application, are the focus of this chapter. 

Interestingly, a fully appropriate model was developed at the same time as the Langmuir model using a similar basic approach. This is the Michaelis-Menten equation which has proved to be so useful in the interpretation of enzyme kinetics and, thereby, understanding the mechanisms of enzyme reactions. Another advantage in using this model is the fact that a graphical presentation of the data is commonly used to obtain the reaction kinetic parameters. Some basic concepts and applications will be presented here but a more complete discussion can be found in a number of texts. ... 

Glu457 E457Q Order bi bi mechanism mechanism of enzyme reaction. 

This chapter gives some examples of how infrared measurements have been applied to studies of mechanisms of enzyme reactions, stereospecificity of reactions, inhibition of reactions, kinetics, properties of substrates, characterization of products of reactions, and identification of organisms by the kinds of enzymatic action displayed by them. 

By the kinetic mechanism of enzyme reactions, we understand (a) the kinetic mechanism, which is a qualitative description of the order of substrate combination and product release from the enzyme, and (b) the determination of rate-limiting steps from quantitative analysis of the kinetic mechanism. 

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